BIOCHEMSITRY

Enzymology
- the science of enzymes to the diagnosis and
treatment of diseases 4 existing structures:
1. Primary structure- refers to the sequence of amino
Catalysts acids joined by peptide bonds. (Amino acid
- compounds that increase the rate of chemical sequence)
reactions. 2. Secondary structure- conformation of the steric
arrangement or conformation of the segments of
Enzymes polypeptide chain (helix)
3. Tertiary structure- arises from the interactions
- are proteins that act as catalysts and provide
among side chains/groups of the polymer chain;
means for regulating the rate of metabolic
folded structure of an enzyme (folded individual
pathways in the body.
peptide)
- Enzyme catalysts bind reactants(substrates) and
4. Quaternary Structure - refers to the relationship
convert them to products and release them.
between subunits wherein subunits perform specific
- Enzymes may be modified during reaction functions. (Aggregation of two or more peptide)
sequences, but will always return to their
original form. *The secondary and tertiary structures are the most
- Substance that catalyzes a given chemical important configurations of the enzyme because these
reaction, cellular catalyst - Biological structures are responsible for the characteristics such as
catalysts that cause reactions in the body to coiling and folding resulting to conformational structure
take place.
- Over 1,500 enzymes and many of which
catalyze the same reactions. Active site
-Refers to the area or portion of an enzyme in
Characteristics of an enzyme: which the substrate is attached with the
- One of the most complicated type of proteins in enzyme molecule
terms of both structure and function -It is where the transformation of the substrate
- Proteins in nature; easily denatured with varying takes place
molecular weight and masses.
- Amphoteric (capable of reacting chemically
either as an acid or as a base.)
- Operate in high rates
- Turnover number of enzymes is 5x106

Enzyme structure (molecular/structural arrangement

of an enzyme molecule)

Classification of enzymes:
-Based on catalytic activity of an enzyme.
-The International Union of Biochemistry (IUB)
enzyme commission categorized all enzymes
into 6 classes
BIOCHEMSITRY
1. Oxidoreductases - Example: ATP + creatine + CK = ADP + creatine
-Enzymes catalyzing oxidation and reduction phosphate
reactions
3. Hydrolases
 Reduction- addition of hydrogen to a
- Enzymes involved in the splitting of molecules with
double bond
water as a part of the reaction process
 Oxidation- removal of hydrogen to
- 3 groups of hydrolases (with examples)
cleave a double bond
(cleave= splitting of chemical bonds)
-Older names are dehydrogenases and oxidases
-Assayed for information/ gives information
regarding heart attacks and liver problems.

- Examples of oxidoreductases - Example: amylase cleaves the C-O-C bonds of

Oxidases starch
o Glucose oxidase
o Cytochrome oxidase 4. LYASES
Dehydrogenase -Enzymes responsible for splitting molecules (lysis)
o LDH -Bonds broken are:
o Iditol DH o C-C bond
o MDH o C-O bond
o Isocitrate DH o C-N bond
o Glucose-6-PO4 DH -Assayed in disorders of skeletal muscles
o Hydroxybutyrate DH -Examples:
- Oxidoreductases acts on o Aldolase
o Glutamate decarboxylase
o Secondary alcohols
o Tryptophan decarboxylase
o Ketones
o Alkenes
o Primary amines 5. ISOMERASES
o Secondary amines -Enzymes responsible for the conversion of one isomer to
o NADH, NADPH another
-It involves the transformation from:
- Example: • Pyruvate + NADH+ + LDH = o Cis-trans
lactate + NAD
o L-D forms
o Aldehyde to ketone
2. Transferases
-All reactions are reversible
- Enzymes that move and interact group of
-No clinical importance
atoms from one molecule to another (amine
-Examples:
or PO4 group)
o Glucose PO4 isomerase
- Gives important information about liver
o Ribose PO4 isomerase
damage
- Examples of transferases
 Aspartic aminotransferase (AST)
 Serum glutamate oxaloacetate
transaminase (SGOT),
 Alanine aminotransferase (ALT)
 Serum glutamate pyruvate transaminase
(SGPT)
 Creatine kinase,
 Gamma glutamyl transferase
 Ornithine carbamyl transferase
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6. Ligases - A.K.A. non-specific, practical name, working name
- Enzymes causing bond formation between - Identical to systematic name and often a simplification of
two molecules to form a longer molecule it
- Example: - Suitable for everyday use
o Ligase enzyme - Uses acronyms and abbreviations
o Amino-acyl-tRNA synthetase – activates - Example: Orthophosphoric monoester phosphorylase –
amino acids before incorporation to the
ALP
polypeptide chain

ENZYME VARIANT
ENZYME NOMENCLATURE - These are the several distinct forms of enzymes
1. Each enzyme was designated according to - Important in the diagnosis of specificity
the reaction it catalyzes Example:
oxidation of glucose – glucose oxidase
2. It is customary to identify enzymes by A. ISOENZYMES
adding the suffix “ase” to the group upon - The multi-chained enzymes
which the enzyme acts - Enzymes of similar activity typically appearing in specific
tissue, organs and cell organelles of organisms and the
Example: Urea - Urease
same species
Uric- Uricase
- Specifically located in tissues
Phosphate esters – phosphatase
- The site of a specific isoenzyme is found and restricted to
Lipid – lipid esters only one tissue
Lactose – lactase o Example: Lactate dehydrogenase: A and M
Starch – amylase ▪ Contains H and M subunits (polypeptide
chains)
3. Naming of enzymes by the use of their ▪ The subunits interact together for a reaction
empirical names Example: trypsin, pepsin to occur
4. Standard system of identifying enzymes
• H4 – LD1 – heart, RBC, and renal tissues
- Formulated by IUB and IUPAC
• H3M – LD2 – heart, RBC and renal
tissues
SYSTEMATIC NAME • H2M2 – LD3 – lungs, lymphocytes,
- Describe the nature of the reactions spleen, pancreas
catalyzed • HM3 – LD4 – liver, skeletal muscle
- Unique numerical code designation (consists • M4 – LD5 – liver, skeletal muscle
of 4 members separated by periods)
- Prefixed with the letter E.C. (Enzyme - Characteristics:
Commission) o Charged molecules – shown in electrophoresis
Example: E.C. 3.1.3.1. – ALP o Mobility in Ion Exchange Resin
E.C. 3.1.3.2 – ACP o Response to activation and inactivation process
▪ E.g. ACP (RBC) – not inhibited by 2%
formaldehyde ACP (prostate) – inhibited by
2% formaldehyde
 1st digit – denotes the class of the enzyme o Relative substrate specificity
 2nd digit – denotes the sub-class of the
▪ E.g. ACP (RBC)- less sensitive to α-
enzyme
naphthyl PO4 substrate
 3rd digit – denotes the subsub-class
o Response to inhibitors
 4th digit – specific serial number given to
each enzyme within its subsub-class
B. HETEROENZYMES
▪ This approach removes all ambiguity about
the enzyme’s identity - Same enzymatic activity, which are specie
specific for different biological species
- e.g., LDH of rabbits and humans
TRIVIAL NAMES
BIOCHEMSITRY
C. ALLOENZYMES B. Bilocular enzyme - These are enzymes that
- Genetically transmitted enzymes are found in the mitochondria and cell sap
- Important in defining the biochemical
Enzyme Kinetics
characteristics of individuals
- Present only in some selected individuals of Where:
the same species- Practical value in forensic • E = enzyme that represents a true catalyst =
medicine and genetics not changed in the reaction
• S = substrate upon which the enzyme acts
ORIGIN OF PLASMA ENZYMES: • P = the reacted substrate = product that
CLASSIFICATION OF ENZYMES IN THE represents a changed molecular species of
substrate
BLOOD
• ES = the postulated enzyme – substrate
A. Plasma Specific Enzymes complex
-Generally secreted by liver into the plasma
-Enzymes exert function in plasma FACTORS AFFECTING THE BINDING
A. Energy – this refers to the activation energy
-Examples:
o Blood clotting mechanisms
B. Molecular compatibility – E + S =
o Complement system and those
commonness and sameness between enzyme
connected with fibrinolysis
and substrate
o Thrombin, factor XII (Hageman
C. Space availability – refers to the number of
factor), Factor X (Stuart factor)
enzymes or substrates that can be reacted
o Precursors (plasminogen activators)
D. Specificity – refers to the particular enzyme
o Serine protease procoagulants
catalyzing a specific substrate
B. Non-plasma specific enzymes
-Enzymes that do not have specific function in Factors Affecting E and S Combination
plasma A. Lock and Key – refers to the active site being
-The plasma lacks activators or coenzymes complementary in shape and size of the
which are necessary for enzyme activity substrate
-2 classes: B. Induced Fit model – refers to the enzyme
changing in shape during binding with substrate.
After binding, the shape of the enzyme
o Enzyme of secretion: complements with the binding site
▪ These are normally secreted enzymes like
AMS
Factors influencing Enzymatic Reaction
▪ Enzymes secreted in plasma at a very high rate
but are rapidly disposed off to normal excretory A. Substrate concentration
channels thus concentration in plasma is a. direct relationship
maintained at low and constant level b. An increase in the concentration of substrate
results to an increase in the rate of enzyme
o Enzymes associated with cellular metabolism activity
▪ Enzymes that carry out their functions within c. No free binding site
the cells in which they are formed
• E.g., CK in heart and ACP in prostate B. Time
gland a. This refers to the condition when the
enzymatic reaction is allowed to take place
Enzymes based on distribution b. If the catalytic activity of an enzyme on the
substrate is fast, it results to a shorter
A. Unilocular Enzymes enzymatic reaction time thereby the enzyme
- These are enzymes found only in the cell sap. is freed and can act again on the remaining
Found only in one location substrate
BIOCHEMSITRY
b. An increase in the enzyme
concentration result to an increase in
the catalytic activity of the enzyme

D. Temperature
2 Phases of Enzyme Reaction
a. Optimum temperature – the point at which
A. First Order Kinetics the enzyme molecule is capable of catalyzing the
• Enzyme concentration is fixed and the substrate with regards to temperature
substrate concentration is varied requirement
• The rate of reaction is almost directly
proportional to substrate concentration at 1. An increase of 10C in temperature
low values (lower substrate concentration results in doubling the rate of enzyme
than enzyme) activity
2. 30-37C or 37-40C – optimum
• The rate of reaction dependent on
temperature
substrate concentration and on enzyme
3. 60-70C – enzyme undergoes
concentration
inactivation and denaturation
4. Further increase in temperature leads
B. Zero Order Kinetics
not to further increase in the rate but
• The rate depends on the enzyme
loss of enzymatic assay
concentration and independent of
5. Some are stored at refrigeration
substrate concentration
temperature (2-8C)
• An increase in the enzyme concentration
results to an increase in the catalytic
activity of the enzyme b. Increased rate in:
1. Increasing movement of molecule
2. Increasing rate at which internal
cellular collision

c. Q10 value – refers to the increased

reaxtion rate for every 10C increase (rate
of reaction is doubled)

E. pH – Hydrogen ion concentration

a. optimum pH – the point at which the reaction
rate is greatest

1. at pH 7-8, many enzymes show maximum

activity
2. pepsin is active at 1.5 and ALP at 10.5

C. Enzyme Concentration
a. Direct relationship
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c. Types of inhibition
I. Reversible inhibition
F. Activators 1. When inhibitors are possible removed from the
a. Required for full enzyme activity system and enzyme is fully restored
b. These metal activators or inorganic entities 2. Physical separation processes that remove
help bind the substrate to the active site by inhibitors
forming ionic bridges a. Dialysis
c. These help substrates in orientation so it is b. Gel filtration
attached to the protein at the proper point end
in the correct configuration II. Irreversible inhibition
1. When inhibitors combine covalently with the
enzyme
Divalent Monovalen Monovalent 2. Physical methods are ineffective in separating
Cations t Cations Cations inhibitors from enzymes
Fe++ Cl- K+
d. Examples of inhibitors
Ca++ Br- Na+ I. Excess substrate
1. Causes competition between substrate
Zn++ NO3- molecules for a single binding site

G. Inhibitors II. Product of Reaction

a. Substances that decrease the rate of 1. A product of reaction may itself be an inhibitor
enzyme reaction if these are present in the of the forward reaction
reaction system III. ES does not break to give products
b. Functions: IV. Chemical substances
I. Binds to the active site, blocking 1. Fluoride
the access of the substrate to the 2. Heparin
enzyme (competitive inhibition) 3. Oxalate
II. Binds elsewhere on the enzyme 4. Cupric
causing change in shape that
5. Tartrate
interferes with substrate binding
(non-competitive)
III. Uncompetitive – inhibitors bind H. Coenzyme concentration
with the ES completely; no product a. Many enzymes require a coenzyme of some
formed sort for the reaction to proceed (vitamins, CoE, A
or B, NAD)
b. These must be present at the proper
concentration for many enzyme reactions to take
place

I. Prosthetic Group
a. These are essentially coenzymes that firmly bind
with enzymes

Enzyme Denaturation
- It refers to the disruption of the structure of
enzyme molecule (3-dimensional structure) that
leads to the loss of enzyme activity
BIOCHEMSITRY
- Denaturing Conditions quantities of polished rice. Symptoms include
o Elevated temperature weakness, neuritis, and in severe cases,
▪ Weakens the stabilizing bonds
▪ Above 60C
o Extremes of pH mental disturbance and heart failure.
▪ Causes unfolding of enzyme molecule
o Radiation c. It can be cured by giving large doses of vitamin
o Frothing B.
o Strong salt solution
o Mechanical trauma 2. Riboflavin (B2) – coenzyme: flavin adenine
dinucleotide (FAD) and flavin mononucleotide ‘
o Time of exposure
a. Milk and meat products
o Chemicals
b. Dermatitis; glossitis; cataracts
- Denaturation may be reversed if the reaction
process has not gone too far and if the 3. Niacin (nicotinic acid B3) – coenzyme:
denaturing agent is removed nicotinamide adenine dinucleotide (NADH)
a. Liver, lean meats, cereals, and legumes
Units of Measurements – proposed by the b. A vitamin deficiency disease characterized
IUPAC and IUB by a rash on exposed body surfaces, diarrhea,
ulcerations in the mouth and mental
A. International Unit (IU) - Defined as the disorientation (pellagra).
amount of enzyme which catalyzes the c. It may be seen among alcoholics who drink
conversion of 1umol of substrate in 1 minute - rather than eat.
Reported in IU/liter of sample 4. Pyridoxine (B6) – coenzyme: pyridoxal
B. Katal - A unit of enzyme activity which phosphate
converts 1 mol of substrate per second - Has not a. Meats, cereals, lentils (legumes)
yet received universal acceptance b. Dermatitis, fatigue, anemia, irritability

Enzyme Regulation 5. Cobalamin (B12) – coenzyme: nicotinamide

1. Feedback control – the concentration of the adenine dinucleotide (NADH)
product influences the rate of reaction. a. Milk and meat products
2. Allosterism – an interaction takes place at a b. Pernicious anemia, malformed RBCs,
position other than the active site but affects the mental disorders
active site, either positively or negatively. c. The administration of vitamin B12, folic acid,
3. Some enzymes (proenzymes or zymogens) liver and stomach extracts have been found
must be activated by removing a small portion of effective in control of this condition.
the polypeptide chains.
6. Ascorbic acid
4. Zymogens are enzymes produced as
a. Plants, fruits, and vegetables
inactive proteins.
b. Scurvy – bleeding gums, slow-healing
5. Enzyme activities are also regulated by
wounds, mental disorders
isoenzymes (isozymes), enzymes that
catalyze the same reactions but vary slightly in 7. Biotin – coenzyme: biocytin
structure. a. Yeasts, meats, dairy products, grains, fruits and
vegetables, intestinal bacteria
THE WATER-SOLUBLE VITAMINS b. Scale skin, fatigue and muscle pains, anemia,
1. Thiamine (B1) – coenzyme: thiamine nausea, weakness; depression
pyrophosphate
a. Fresh vegetables, husks of cereal grains, 8. Folic acid – coenzyme: tetrahydro folic acid
liver and other organ meats a. Organ meats, fresh green vegetables
b. Abnormal red and white blood cells (anemia);
b. A vitamin deficiency disease seen
intestinal tract disturbances
particularly among those who eat large
BIOCHEMSITRY
9. Pantothenic acid – coenzyme: coenzyme a. A Infants exhibit diarrhea, vomiting, and a “cabbage-
a. Most foods, especially liver, meat, cereals,like”
milk,odor and fail to thrive.
fresh vegetables b. Without treatment, death from liver failure ensues 6-8
b. Vomiting, abdominal distress, insomnia months.
Most Common Disturbances c. Treatment: diet low in tyrosine, phenylalanine,
1. Kwashiorkor – disease resulting from a deficiency and methionine.
of dietary protein relative to caloric intake (protein-
energy malnutrition). Digestion is an activity that is done as part of daily
a. The disorder occurs most commonly in young living. All living organisms, primarily animals and
children in developing countries when mothers’ humans, entail digestion to sustain daily activities and
breast milk no longer provides enough protein, essential needs. Digestion requires the presence of
and other protein-rich foods are no given in enzymes, co-enzymes and cofactors. This process
sufficient quantity. when successful will result in the production of
b. The number of calories in the diet of corn meal building blocks of the different biomolecules which are
is sufficient, but corn is deficient in lysine and necessary in performing body building, regulatory, and
tryptophan. As a result, a child fails to grow, energy-giving functions. Disruption in this process will
becomes lethargic, and has an enlarged abdomen impact the health status of an individual.
from hypo protein edema due to the inability to DIGESTION is referred to as the disintegration of the
properly build proteins. naturally occurring foodstuff into absorbable forms. It
includes the hydrolysis of starch into
2. Marasmus – results from slow starvation monosaccharides, proteins to amino acids, and fats
caused by deficiency not only of protein but also into fatty acids and glycerol.
of calories and other nutrients
TWO FACTORS IN DIGESTION:
Primary factor includes the different enzymes found
3. Anemia – blood condition involving an abnormal
reduction in the number of RBCs or in their hemoglobin in the juices of the different portions of the digestive
tract. These are necessary in the conversion of
content.
complex molecules to simple and absorbable forms.
4. Gout – caused by faulty metabolism of uric acid
produced in the body by breakdown of proteins. Secondary factors include the following:
▪ Factors: diet rich in malt liquors, wines, and certain  Cooking ruptures walls of starch granules,
types of protein and about 95% are men. softening of connective tissue (make them
accessible for e action). It also improves the taste
5. Phenylketonuria (PKU) – this is due to the absence and appearance of food which in turn stimulate
of the enzyme phenylalanine hydrolase which converts secretion of digestive enzymes
phenylalanine to tyrosine. Phenylalanine is instead  Mastication breaks down the food and increases
converted to phenyl pyruvic acid which impairs normal surface area for enzymes to act. It is a
development of the child’s brain leading to mental mechanical stimulus for the flow of saliva and
retardation. digestive juices.
 movements of the stomach and intestines or
6. Albinism – this is due to the absence of tyrosinase, what is known as peristalsis.
which is necessary for the formation of melanin.  absorption from the intestines,
 autodigestion such as in the ripening of fruits.
7. Alkaptonuria – this is due to the absence of the
homogentisic acid oxygenase (homogentisic acid →
acetate and fumarate).
Digestion of food undergoes several processes in
▪ A disturbance of metabolism in which the skin of the
different parts of the digestive system. This is
face, the whites of the eyes, and other tissues such as
referred to as the physical movement and
muscle and cartilage become discolored brown. (The
breakdown of food which includes:
urine is also a dark, brownish color.)

1. Swallowing
8. Tyrosinosis – this is due to the absence of
hydroxyphenyl pyruvic acid oxygenase which converts a. Buccal stage
hyroxyphenylpyuvic acid to homogentisic acid. I. Bolus is pushed toward the pharynx
BIOCHEMSITRY
II. Voluntary movement
b. Pharyngeal and Esophageal stage
I. Bolus (masticated food with saliva) to
pharynx to esophagus to stomach
II. Involuntary movement

2. Peristalsis in the stomach Different Stages of Digestion CHEMICAL BREAKDOWN

a. Mixes contents and forces chime thru OF FOOD
the pylorus
b. Three waves travel down the stomach A. MOUTH
one at a time Mechanical digestion in the mouth
I. Each beginning every 20 seconds  Chewing or mastication
near the midpoint of the stomach,  Food manipulated by tongue, ground by teeth, and
lasting about one minute mixed with saliva
 Forms bolus
c. The rate of emptying of the stomach is
determined largely by the strength of Chemical digestion in the mouth
contraction
 hydrolysis of starch by salivary amylase
d. Feedback from the duodenum
(ptyalin)
regulates gastric emptying
 takes place in the buccal cavity and to a
e. 2 mechanisms that inhibit gastric
certain extent in the fundic end of the
motility
stomach
I. Enterogastric reflex –
 Starch & glycogen → maltose
neuronal
II. Enterogastrone – hormonal
SALIVA
Chyme – partially digested food with
 Colorless slightly viscid, opalescent fluid which
gastric juices
is a mixture of secretions of the three pairs of
3. Contraction of the small intestines salivary glands
a. Segmenting – rhythmic  Parotid gland – section is watery and
contractions along a section rich in ptyalin
dividing it into segments  Sublingual gland – secretion is more
I. Primarily a mixing action viscid containing mucin and poorer in
b. Gastroileal reflex – the increase ptyalin
in ileal peristalsis and frequency of  Average secretion per day is 1,500 ml
opening of the ileocecal valve due  99.42 % water o 0.58 % solid
to the ingestion of food  2/3 = org. matter (mucin, ptyalin, urea,
glucose, lactic acid…)
 1/3 = inorg. Salts (Cl- , HCO3 - of Na, K, Ca,
SO4 - and PO4 - )
 pH: 7.0 – 7.3 (active stimulation)
 6.4 – 6.9 (resting saliva)
BIOCHEMSITRY
stimulates the secretion of gastric juice,
pancreatic juice, intestinal juice and bile

Factors influencing the secretion of

saliva
Gastric Juice
- Average secretion per day is 2-3 liters
- Contributed by three types of cells from the gastric
glands
o Parietal cells – secrete HCl (0.17N), pH 0.87
Salivary amylase o Chief cells – secrete pepsin
o Mucosal cells – secrete mucin
 Also known as ptyalin
 Endoamylase which acts only on the Composition
alpha 1,4-glycosidic linkages • 99.4 % water
 Splits starch into the disaccharide • 0.6 % solid
maltose • organic constituents: mucin, pepsin, & small
 activators: Cl- & Br - ; I - & NO3 amount of lipase
 Unstable below pH 4 – 5 • Inorganic Constituents: HCl, KCl & PO4
 Inactivated by pepsin

B. STOMACH Pepsin
Gastric Digestion • principal digestive constituent of the gastric
 Mainly concerned with the digestion of juice
proteins thru the action of the enzyme • pepsinogen – activated by HCl; Inactivated
pepsin and HCl at neutral pH or alkaline pH
 Pepsin – initiates protein digestion
producing proteoses, peptones and
polypeptides
• autocatalytic
Pepsinogen • Optimum activity: pH 1.5 – 2.5
(Chief cell) • An Endopeptidase that acts on peptide bonds

3 Phases in Gastric Digestions Mucin

1. Psychic phase • not digested by pepsin
a. Stimulation of gastric secretion due to the • Protects the mucous membrane of the stomach
smell, sight, taste and thought of food • Buffers the HCl
b. Gastrin – secreted by G cells in the pyloric • Promotes absorption of Vit. B12
region of the stomach, it stimulates the Renin – milk –curdling enzyme found in the gastric
secretion of an acid rich gastric juice juice of newborn infants - The gastric juice on
2. Gastric Phase infants contain little or no pepsin but high
a. Initiated by food in the stomach concentration of HCl
b. Secretagogue – present in certain food
which stimulates the secretion of gastrin
(hormone from the pyloric mucosa) Inhibitors of Gastric Secretion
3. Intestinal phase  Enterogastrone – produced from the
a. Initiated by digestive products in the upper presence of fats in the intestines which inhibits
small intestine gastric secretion and motility
b. Secretin – a hormone released by the  Urogastrone – found in urine: similar to
duodenum acting on the stomach, it enterogastrone
 Acids inhibitors
BIOCHEMSITRY
• 0.03 N HCl – slows secretion Intestinal digestion does not focus on the
• 0.1 N HCl – inhibits parietal cells small intestines alone but also includes the
pancreas and the bile

Functions of HCl
1. Provide suitable pH for protein digestion by
pepsin
2. Exerts preliminary swelling, denaturing and
hydrolyzing effect on proteins
3. Activates pepsinogen
4. Facilitates absorption of iron
5. Causes hydrolysis of disaccharides
6. Stimulates secretion of secretin
7. Exerts germicidal action

Pathological Variation of HCl

▪ Achloridia:
- absence of free HCl
- seen in Pernicious anemia

▪ Achylia gastrica
- partial or complete absence of gastric juice
- indicates degeneration of the gastric glands
▪ Hypochloridia:
- suggestive of chronic gastritis or gastric
carcinoma
▪ Hyperchloridia:
- suggestive of peptic ulcer, cholecystitis

Intestinal Digestion
C. INTESTINES
The last site of digestion and the site of
absorption is the small intestines. Most
enzymes are present in this particular site
thus, chemical digestion is at the most.
BIOCHEMSITRY
3. Carboxypeptidase - Zinc-containing enzyme.
Exopeptidase attacking the peptide linkage nearest
the free hydroxyl group

INTESTINAL DIGESTION
Pancreatic Juice 4. Pancreatic amylase - Also known as diastase and
- Secreted by the acinar cells of the pancreas amylopepsin. Converts starch and glycogen into
(500ml/day) maltose which is immediately acted upon by the
- Clear, watery solution made up of 98.7% water enzyme maltase.
and 1.3% solids 5. Pancreatic Lipase - Also known as steapsin. It
- It is the most alkaline of the normal body fluids exhibits weak lipolytic effect. Action is potentiated by
(pH 7.5 – 8.2) due to its bicarbonate content bile acids, calcium and certain amino acids. It splits
fats into monoglycerides, fatty acids and glycerol
o Organic constituents (1/3)
▪ Trypsin, chymotrypsin (proteolytic enzymes) 6. Nucleodepolymerase - Ribonucleases and
▪ Steapsin (lipolytic) deoxyribonucleases. They hydrolyze the
▪ Diastase (amylolytic) corresponding nucleic acid into mononucleotides
▪ Nucleolytic enzymes
Intestinal Juice (Succus Intericus)
o Inorganic constituents (2/3) - Combined secretion of the intestinal glands at
▪ Sodium different portions: duodenum, jejunum, ileum
▪ Potassium - Viscous and turbid fluid due to mucin and
▪ Calcium desquamated epithelial cells
▪ Bicarbonate Enterocrinin – hormone secreted by the intestinal
▪ Chlorides mucosa and stimulates the mucosal glands to
▪ Phosphates increase volume of fluid and the content of enzyme

Regulation of Pancreatic Secretion Enzymes in Intestinal Juice

1. Vagal Stimulation 1. Carbohydrases
a. Secretion is rich in enzymes but less volume a. Maltase
b. Occurs during cephalic and gastric secretion b. Lactase
2. Hormonal stimulation c. Sucrose (invertase)
a. Secretin – stimulates secretion of a fluid of
high volume and bicarbonate content 2. Peptidases
b. Pancreozymin – stimulates enzyme a. Aminopeptidase – exopeptidase, attacks the
secretion peptide linkage of the terminal amino acid
containing free amine group which requires Mg+
Enzymes in the Pancreatic Juice + or Mn++
1. Trypsin - Protein splitting enzyme and an b. Tripeptidases and Dipeptidases – split
endopeptidase. Secreted as trypsinogen and tripeptides and dipeptides into their constituent
initially activated as trypsin by enterokinase from amino acids which require Co++ and Mn++
succus entericus. Acts upon peptide linkages.
Splits proteins and products of pepsin digestion
into peptides
2. Chymotrypsin - Endopeptidase acting on
peptide bonds involving phenylalanine, tyrosine
and tryptophan. Activated by trypsin. Powerful
milk-curdling effect
o Peptidases
▪ All intestinal enzymes except two
▪ Split peptides into amino acids
BIOCHEMSITRY
Liver Bile Gall Bladder Bile
▪1-4% ▪ Solids: 4 - 17%
▪ Less viscous ▪ more viscous
▪ Golden ▪ dark yellow-green
yellow ▪ pH 5.5
▪ pH 7 - 8.5
Bile acids
1. Cholic acid – 26 – 60% of the total
2. Chenodeoxycholic acid – 30 – 50%
3. Deoxycholic acid – 5 – 25%
o These bile acids are conjugated with
glycine or taurine to form bile salts

At this figure, it shows the function of both the Functions of bile

aminopeptidase and carboxypeptidase. Since both 1. Activate steapsin
are exopeptidases, they act on the peptide linkage 2. Aid in absorption of fat and fat-soluble
of the terminal amino acid (the one in circle) which substances by forming water-soluble complex
is the amine group for aminopeptidase and carboxyl (hydrotropic effect)
group for carboxypeptidase 3. Enhance digestion of fat (emulsification) -
lowers surface tension, and disperse in an
3.Nucleotidases (Nucleophosphatases) emulsion which enhances digestion of fat
– split the nucleotides into phosphoric acid 4. Choleretics (stimulate secretion of bile)
nucleosides 5. Maintain cholesterol in solution
Nucleotides Nucleoside +
Phosphoric acid Bile Pigments
▪ From the degradation of hemoglobin
4. Nucleosidases – purine nucleosidase; ➢ Biliverdin
pyrimidine nucleosidase ➢ Bilirubin (formed from the reduction of
Nucleoside sugar + base biliverdin)

Absorption - Occurs almost exclusively in the

Bile - Clear, golden yellow, slightly viscid fluid, small intestine. Simple sugars, amino acids,
secreted by the liver cells. Average secretion of short chain fatty acids, and glycerol are
500 – 700 ml/day. Stored in the gall bladder where absorbed into blood stream via capillary network
it undergoes concentration. Gall bladder bile is of villi. Products of lipid digestion are absorbed
more concentrated, more viscous and darker as chylomicrons into intestinal lymphatics via
yellow-green in color. central lacteal villi
Cholecystokinin – hormone which stimulates the
discharge of bile into the bowel (relaxation of the
Chemical Changes in the Large Intestine
sphincter Oddi and Contraction of the gall bladder)
Cholagogue – substance that stimulates the flow D. LARGE INTESTINES- the large intestines
of bile produce no digestive enzymes; it is still a part of
➢ Solid content (1 - 4%) the digestive system. It functions primarily on the
absorption of water and electrolytes and the
*Organic *Inorganic elimination of feces. There are chemical changes
components (3/4) components that occur in the large intestines.
▪ Bile acids ▪ HCO3 –
▪ Bile pigments Chemical Changes in the large Intestines
▪ Cl
▪ Bilirubin o The semi-liquid residue which has escaped
▪ Na
▪ Cholesterol digestion and absorption are passed into the large
▪K
▪ Small amount of intestines. The presence of intestinal
▪ phospholipid microorganisms disintegrates these organic
(Lecithin) residues into simpler fragments
▪ Mucin, Urea, ALP
BIOCHEMSITRY
combination of the toxic substances or
one of its metabolites with a compound
occurring normally in the kidney.
Occurs chiefly in the liver

1. Fermentation - Bacterial degradation of Conjugating agents

carbohydrates under anaerobic conditions.
Products are: o Acetic acid o Glycine
o Organic acids o Cysteine o Methyl group
▪ Lactic acid o Glucoronic oacid
Sulfuric acid
▪ Formic acid o Glutamine o Thiosulfate
▪ Propionic acid
▪ Succinic acid
o Gases
▪ Methane
▪ Carbon dioxide
▪ Hydrogen gas

2. Putrefaction - Bacterial decomposition of

protein under anaerobic conditions
Tryptophan Indole + skatole

3. Deamination - Removal of amine group

from simple amino acids to form short-chain
organic acids

4. Decarboxylation - Removal of carboxyl

group forming amines

Detoxification - Includes all processes by

which noxious substances are rendered less
harmful or more easily excreted

Reactions Involved
1. Oxidation - One of the most important
means of detoxification. Example: Ethyl
alcohol + Oxygen = carbon dioxide +
water
2. Reduction – has minor role in
detoxification
3. Hydrolysis – some drugs used for
therapy are hydrolyzed in the body
Acetylsalicylic acid = salicylic acid +
acetic acid.
4. Conjugation - Process called upon
whenever oxidation becomes
ineffective. Brought about by the
BIOCHEMSITRY

INTRODUCTION:
The name carbohydrate originally meant a
compound with the empirical formula
CH2O, literally, a hydrate of carbon. This
definition has been broadened to include A. According to number of saccharide units
aldehydes and ketones having two or - Monosaccharides
more hydroxyl groups. Among the o The simplest carbohydrate – has only one
compounds that fall into the class of saccharide unit o Cannot be broken into smaller CHO
carbohydrates are the starches, cellulose, molecules by hydrolysis
glycogen and the sugars. The
carbohydrates are important source of - Disacchrides
energy for all organisms and form the o Contains two monosaccharide units o It can be
supporting tissue of plants and some hydrolyzed to give two monosaccharide units
animals. There are three important
classes of carbohydrates: the - Oligosaccharide
monosaccharides, disaccharides and the o Polymers made up of two to 10 (2-10)
polysaccharides. (Holtzclaw and monosaccharide units
Robinson, 1988).
- Polysaccharides
CARBOHYDRATES o Giant polymers made of many monosaccharide
- Commonly known as sugars. They are units o The most complex CHO because they contain
defined as polyhydroxy aldehydes or more than 10 saccharide units
polyhydroxy ketones or substances that
yield these compounds when hydrolyzed. B. According to number of carbon atoms
 Trioses – with three carbon atoms
IMPORTANCE AND FUNCTIONS OF  Tetroses – with four carbon atoms
CARBOHYDRATES  Pentoses – with five carbon atoms
1. Energy Yielding Nutrients – they serve  Hexoses – with six carbon atoms
as primary source of metabolic fuel  Heptoses – with seven carbon atoms
needed by a living body and as means to
store and reserve energy in the form of Theoretically, a monosaccharide can have any
glycogen number of carbons greater than three, but only
2. Serve as structural components of the monosaccharide of three to seven carbons are
living cells - as carbohydrates combine commonly found in the biosphere
with proteins, they from glycoproteins and
proteoglycans that are very important C. According to its functional group
components of the cell membrane o the functional group of carbohydrates is the carbonyl
3. Serve as structural framework – for group (-C=O)
DNA and RNA as part of nucleotides  Aldose - polyhydroxy aldehyde and the
4. Mediate Interaction between cells – carbonyl group is found at one of the terminal
blood types are determined by specific sides of the hydrocarbon chain
membrane bound CHO  Ketose - polyhydroxy ketone and the carbonyl
5. Building materials – cellulose is found in group is found in between 2 hydrocarbon
wood, cotton, paper groups

CLASSIFICATION OF CARBOHYDRATES
- The simplest structural unit of
carbohydrate is known as saccharide
- In Latin, Saccharine means sugar
BIOCHEMSITRY

Epimers: - two sugars which differ only in the

configuration around a single C atom

D. As a furanose or pyranose
- Depends on whether the cyclic structure of
the carbohydrate is related to that of the five
Asymmetric Carbon - refers to the C atom in the
or six-membered ring compound furan or
structure of a sugar to which 4 different radicals are
pyran respectively
attached.

E. As Alpha or beta configuration

• the asymmetric carbon gives rise to the
- Based on the –H and –OH groups about a
following:
specific chiral carbon in the cyclic form of the
monosaccharide

Optical activity/ Mutarotation

- the ability of a sugar solution to bend or deflect plane
of polarized light.
- (d or + ) DEXTROROTATORY (to the right)
BIOCHEMSITRY
- ( l or - ) LEVOROTATORY (to the left) 5. Heptoses (C7H14O7) – mannoheptose,
mannoheptulose

Chemical structure of monosaccharides

1. The carbon skeleton is unbranched
2. All the Carbon atom except one has a hydroxyl (-OH)
group
Enantiomers (mirror-image isomers)
3. One has a carbonyl oxygen which may be in
- Stereoisomerism/ enantiomerism terminal position to give rise to an aldehyde (aldose),
o Depends on the spatial orientation of the –H or may be located on the second carbon atom giving
and –OH group attached to the carbon atom rise to an ketone (Ketose)
adjacent to the terminal primary alcohol group 4. The terms aldose for hydroxyaldehydes and ketose
o the ability to form two sugars which are for hydroxyketones specify the functional group of a
mirror images to each other (Disomer or L- monosaccharide
isomer). 5. The general formula of carbohydrates: Cn(H2O)n
o The configuration is based on the location of Where n = number of carbon atoms
the –OH linked to the C atom which is the 6. It includes both the aldehyde and the ketone groups
next to the terminal. (functional groups)
7. Hydroxyl groups are attached to each C atoms,
except that of the carbonyl group
• D-isomer: -OH is on the RIGHT of the C atom
adjacent to the terminal primary alcohol group
• L-isomer: -OH is on the LEFT of the C atom IMPORTANT MONOSACCHARIDES
adjacent to the terminal primary alcohol group. 1. Diose – a monosaccharide with 2 carbon sugars.
They are the simplest carbohydrates
o Example: Glycoaldehyde

2. Triose – a monosaccharide with three carbon atoms.

Glyceraldehyde
o Produced from the breakdown of larger
monosaccharides
o D-glyceraldehyde with D-glyceraldehyde – 3 –
phosphate is an intermediate in the metabolic
pathway of glycolysis (conversion of glucose to
lactic acid)

3. Tetroses – carbohydrates containing 4 carbon atoms

– Examples:
o Erythrose – aldehyde tetrose/aldotetrose
o Erythrulose – ketone tetrose/ketotetrose
o Threose – aldehyde tetrose/aldotetrose
MONOSACCHARIDES
- Simplest carbohydrates which cannot be broken 4. Pentose – monosaccharides with 5 carbon atoms,
down into smaller carbohydrate molecules. the most widely distributed sugars in the living
systems
1. Trioses (C3H6O3) – glyceraldehyde,
dihydroxyacetone - Ribose
2. Tetroses (C4H8O4) – erthyrose, erythrulose o Component of ribonucleic acid (RNA), RNA
3. Pentoses (C5H10O5) – xylose, ribose, sugar
deoxyribose, arabinose, rhamnose o RNA – is a polymeric compound that plays a
4. Hexoses (C6H12O6) – glucose, galactose, major role in the synthesis of protein molecules
mannose, fructose
- Deoxyribose
o DNA sugar
BIOCHEMSITRY
o DNA – is a compound which transmitso geneticLiver can convert fructose to glucose
information from parent to offspring by directing the
synthesis of protein molecules NOTE: Fructose: Present in honey in equal amount
with glucose. It is sometimes used as dietary sugar
- Xylose because less is needed with the same sweetness
o Found in nuts o Also known as sugar alcohol o It - Levulose is another name for it
is a sugar that is not normally metabolized because it is levorotatory
o It is used to detect CHO malabsorption
• Xylose excretion test

• After a known amount of D-xylose has been - Mannose

given to a patient, its appearance in the urine is o D-Mannose is the 2-epimer of glucose
observed • exists primarily as sweet-tasting α- (67%)
• In normal individuals, 65% of the xylose or as a bitter-tasting β- (33%) anomer of
should be absorbed intact and excreted in the the pyranose
urine in 5 hours o Naturally-occuring aldohexose
• A decreased amount of D-xylose in the urine o Not found free in nature but is widely
indicates malabsorption due to intestinal distributed in the form of polysaccharide.
disease o L-Mannose is not normally used in biological
systems
- Arabinose
o Found in nuts o Known as gum sugar DISACCHARIDES
- Composed of two saccharide groups
- Formed when two monosaccharide
5. Hexoses – monosaccharide with 6 carbon atoms molecules combine by splitting out a
o The aldohexoses, ketohexoses and molecule of water
aldopentoses will receive special attention
- The glycosidic linkage that joins the two
since they include the most important
sugars always involves the hemiacetal –
monosaccharides in living systems
OH group of one sugar and one of the OH
- Glucose (grape sugar/blood sugar/plasma groups of the other monosaccharide
sugar/dextrose)
o Most common source of cellular ATP and from
which most complex carbohydrates are made
from
o Natural sugar mostly in the D form Blood
concn: 80 – 100 mg/Dl

NOTE: Glucose - exists in D-glucose: aka Dextrose

because it is dextrorotatory; - does NOT require
further digestion and may be given IV to patients
who cannot take in food by mouth

- D-Galactose Important Disaccharides

o brain sugar – D-glucose is found in the brain and
nervous tissue in the form of glycolipids 1. Maltose
o An aldohexose; Less than half as sweet as glucose - Malt sugar
o Not a natural sugar - Broken down into 2 molecules of glucose
o Has the fastest rate of absorption in the intestines - Linkage: alpha - 1,4
- Found in combined form as starch and is one
- D-Fructose (levulose/fruit sugar) of the intermediate products in the digestion
o Sweetest sugar of starch
o A natural ketohexose; occurs in honey - Derived from “malting” (soaking, germinating
o Serves as a source of energy for the sperm cells and drying of grains such as barley)
BIOCHEMSITRY
- The malt produced includes malt starch- Considered
and as a non-reducing sugar, a sugar which
enzymes that are able to convert malt starch
does not react with Tollen’s or Benedict’s reagent
into maltose, which is then fermented - Main
to sources: sugar and sugar beets
produce alcohol - When sucrose undergoes hydrolysis, it produces an
equimolar mixture of glucose and fructose called
INVERT SUGAR through the action of the enzyme
SUCRASE or INVERTASE

2. Cellobiose
- Composed of 2 glucose molecules
- Linkage: beta – 1,4 POLYSACCHARIDES
- Produced from the breakdown of the polysaccharide - General formula: (C6H10O5)x
cellulose - Made up of several saccharide groups
o Mammalian digestive tracts do not secrete enzymes - they do not exhibit reducing properties
that can break the beta – 1,4 linkages between 2 - Made up of several hexose molecules minus
glucose molecules the corresponding molecules of water

Properties of polysaccharides
- White, tasteless, amorphous compounds
- X-ray analysis: crystalline
- No reducing property; do not form osazone
crystals
- High MW; mostly are insoluble
- Non-fermentable by yeast
- Upon hydrolysis, yield simple sugars and sugar
3. Lactose derivatives
- Also known as milk sugar - Polysaccharides with large MW are antigenic
- Made by combining B-D-Galactose and D-glucose
- Linkage: Beta-1,4 Homopolysaccharides
- In the body, it is broken down by the action of the - These are polysaccharides which on
enzyme known as LACTASE hydrolysis yield only one kind of
- Deficiency of the enzyme leads to inability to absorb monosaccharide
lactose and the condition called LACTASE
DEFFICIENCY SYNDROME or LACTOSE 1. Starch – found abundantly in the plant
INTOLERANCE kingdom particularly in fruits, cereals,
- This condition is controlled by eliminating all dietary seeds, bulbs and tubers. Most important
sources of lactose (e.g. dairy products, some constituent of the human diet. Occurs in the
medications) form of granules

2. Inulin - Found in the bulb of onions and

4. Sucrose garlic. White, odorless, tasteless powder
- Also known as table sugar soluble in hot water. Upon hydrolysis (by the
- Made by combining alpha-D-glucose and beta-D- action of either acid or the enzyme INULASE)
fructose yields fructose. Clinical significance: study of
- Linkage: alpha,beta - linkage renal function; inulin is easily excreted
BIOCHEMSITRY
through the kidneys when injectedo Rayon – fiber made from cellulose
intravenously o Cellophane – transparent cellulose sheeting
o Cellulose + HNO3 + H2SO4 = nitrocellulose
3. Glycogen - Also called animal starch. Found (cellulose nitrate)
in the liver as storage material and in the • With 12.5 – 13.4% N = guncotton
muscles as source of energy. Occurs in yeast, • With 11 – 12% N = celluloid (used in
algae and fungi; abundant oysters. Structure plastics and photographic films)
is similar to that of amylopectin except thato Cellulose + acetic acid (or acetic anhydride) =
branching (via alpha-1,6 linkages) occurs cellulose acetate
about 8-12 glucose units (24 – 30 glucose • Used as a substitute for celluloid
units for amylopectin) • Fabric, upholstery and cigarette filters
o Cellulose plays an important role in human
physiology by furnishing bulk or roughage
which stimulates peristalsis, thus promoting the
- Monosaccharides like glucose are synthesized evacuation of the bowel
and stored in the muscles and liver as
glycogen
- When the body needs them for heat and
energy purposes, they are broken down to D 6. Hemicellulose
glucose to supply the physiological o Hydrolyzed upon boiling with mineral acids
requirement o Products: pentoses and hexoses.

a. Pentosans (C5H8O4)x: widely distributed in the

4. Dextrin - Intermediary products of starch plant kingdom
hydrolysis - Amorphous, white powder • E.g gum Arabic
• Liberates pentose upon hydrolysis

b. Hexosans (C6H10O5)x: represented by

- Uses:
galactans (widely distributed in plants) and give
o Used as mucilage rise to galactose upon hydrolysis
o Used in infant feeding; prevents the formation • E.g. agar-agar has very little food value but has
of large, heavy curds or milk in the baby’s been found to be very efficient in relieving chronic
stomach, thus facilitating digestion constipation; also used in making culture media
o Found in some breakfast foods and malt
preparation c. Hexo-pentosans: e.g. pectin – colloidal CHO
responsible for the jellying properties of fruits
5. Cellulose - Most abundant organic compound.
Forms the supporting structure of plants. Purest
source: cotton. Negative to the iodine test. Heteropolysaccharides
Structure: the monosaccharide units of cellulose - Yield mixtures of monosaccharides and derived
are beta-glucose molecules connected by beta- products
1,4 linkages into cellobiose units - Nitrogen-containing mucopolysaccharides
o Humans cannot digest cellulose due to
the absence of the enzyme capable of o Neutral mucopolysaccharide
cleaving the beta-1,4 linkage • Made up of N-acetyl-hexosamine and
hexose
• E.g. those occurring in bacteria and the
so-called “mucoids” including important
immunological specific blood group
substances

o Acid mucopolysaccharide
•Contains acetylhexosamine, hexuronic
- Uses of Cellulose acid, sulfate or phosphate
BIOCHEMSITRY
• examples of mucopolysaccharide: o Higher CHO (e.g. starch) – insoluble,
• Those containing sulfate form colloidal solutions
o Cellulose – practically insoluble
o Chondroitin sulfate of the
cartilage tissue - contains 3. Relative Sweetness of Sugars
Nacetylgalactosamine, glucuronic
sugars Relative Sugar substitutes (common
acid and sulfate sweetness brand names)
o Chondroitin sulfate of the skinFructose 100 Sucralose (Splenda®)
has 1-iduronic acid instead Invert of sugar 75 Saccharin (sweet n low®)
glucuronic acid Sucrose 58 Acesulfame potassium
o Heparin – glucosamine N-sulfate, (Sunette®, Sweet One®)
glucuronic acid and sulfate Glucose 43 Aspartame (Equal®,
Nutrasweet®)
Maltose 19
Galactose 19
o Hyaluronic acid
Lactose 9.2
• Main constituent of the ground substance of
connective tissues
• Found in synovial fluid, pleural fluid, vitreous
humor and Wharton’s jelly
• Made of d-glucuronic acid, d-glucosamine and Chemical Properties
acetic acid 1. Reducing power - All mono and di containing the
• Function: potentially free aldehyde or ketone group
• Lubricant possesses reducing properties; reduce alkaline
• Cementing substance which allows metals and are transformed into organic acids
passage of metabolites but not of the
infective organisms Benedict’s test
Reagent: CuSO4 in NaOH Na-citrate
• It is fragmented by hyaluronidase (spreading Positive result: Reddish brown to red precipitate
factor), an enzyme found in bacteria, sperm
and in the poisonous secretions of reptiles
and other animals

o Heparin
• Generated by certain types of cells lining
Fehling’s test
arterial blood vessels and by the lung tissues
Reagent: CuSO4 in NaOH Na-tartrate
• Powerful inhibitor of blood clotting thus
Positive result: Reddish brown to red precipitate
preventing intravascular coagulation
• In practice, it is used to prevent clotting of blood
Nylander’s test
specimens
Reagent: Bismuth subnitrate
Positive result: Black-colored solution
GENERAL PROPERTIES OF CARBOHYDRATES
Physical properties
1. Appearance
- Mono and disaccharides
– white and crystalline
- Starches – amorphous powder Barfoed’s test
- Cellulose – fibrous Reagent: Cupric acetate in weak acetic acid
2. Solubility (in ordinary solvents) Positive result: Red precipitate
- Inversely proportional to the complexity of
their structures 2. Osazone formation
o Mono and di – more soluble in water
BIOCHEMSITRY
- Reducing sugars form characteristic osazone Positive Result: Red color (for galactose)
crystals when heated with an excess of
phenylhydrazine (C6H5NHNH2)
- Attributed to the presence of aldehyde Test or for Pentoses
ketone group in their molecules A. Bial’s Orcinol-HCl test
Reagent:
- Due to this property, sugars can be identified Bial’s reagent: Orcinol in 95%
from a mixed sample Ethanol 10% FeCl3.6H2O 2 ml Orcinol-HCl (+ 1
ml sugar solution)
Positive Result: green solution to deep blue
product
Use: To distinguish a pentose from a hexose

B. Tauber’s Benzidine Test

Reagent: 4% solution of benzedine in glacial
acetic acid (tauber’s reagent) 1 ml Benzidine (+
2 drops of sugar solution)
Positive result: Violet color
Use: test for the presence of pentoses
3. Action of alkalies 5.Fermentation - decomposition of carbohydrates
- Moore’s test – when a solution of reducing sugar is brought about by the action of microorganisms
heated with an alkali (NaOH), it turns yellow to 9yeast, molds, bacteria)). When yeast is added to
orange, and finally dark brown liberating the odor or sugar solution, ethyl alcohol and carbon dioxide are
caramel, which becomes more marked upon produced
acidification. C6H12O6 = C2H5OH + CO2

Zymase – enzyme in the yeast which produces

4. Action of Acids - monosaccharides when acted
fragmentation of the sugar molecule
upon by concentrated acids boiling temperature are
o This process in utilized in the manufacture of
dehydrated forming Furfural if the sugar is pentose;
beverages and other industrial products
the sugar is a hexose, Hydroxymethyl furfural
(oxonium salts) is formed
6. Oxidation - except sucrose, disaccharides and
monosaccharides especially Aldoses are more
A.Molisch test
Reagent: Alpha-naphthol and 95% ethyl readily oxidized forming sugar acids
alcohol and Conc. H2SO4  Oxidation of aldehyde group – forms
Positive Result: Violet ring at the junction of “Aldonic acids”
the two liquids  Oxidation of Primary ROH – forms
Use: General test for carbohydrates “Uronic acids”
 Oxidation of both – forms “Aldaric acids”
B.Anthrone test
Reagent: Anthrone (Keto form of 9- 7. Reduction - all sugars except sucrose undergo
hydroxyanthracene or 10-hydroanthracene-9- reduction with the absorption of energy and the
one) & Conc. H2SO4 Positive Result: Blue formation of products convertible into fats
or green color Reduction of an aldose produces one
Use: for rapid detection of carbohydrates in alcohol
samples like body fluids and can be used for Glucose + 2H = Sorbitol
cellulose assays Galactose + 2H = Dulcitol

C.Seliwanoff’s Test Reduction of a ketose sugar yields two

Reagent: Resorcinol and HCl Positive alcohols
Result: red color (specific for ketoses) Use: Fructose + 2H = mannitol + Sorbitol
used to differentiate aldoses from ketoses - these alcohols are used in culture media for
the identification and differentiation of bacteria
D.Tollen’s Phloroglucinol test
Reagent: Phloroglucinol
BIOCHEMSITRY
8. Esterification - the presence of the primary alcohol
group (-CH2OH) in the sugar molecule make it
reactive with an acid
2 classes of amylases
DIGESTION AND ABSORPTION
- For complex carbohydrates to be of value, these Alpha – amylases (alpha-1,4 glucan 4
should undergo digestion glucanohydrolase)
• Found in pancreatic and salivary juices
• Saccharogenic amylase
60% of food ingested is complex carbohydrates
• Found in human GIT
 Starch and glycogen – fragmented into simple
monosaccharides • Split alpha 1,4 glycosidic bonds (except those of
 Cellulose and pentosans – no digestive enzymes maltose) in random fashion
for humans
 Cellulose – cellulase – bacterial enzyme that acts
on cellulose, however, nutritive value is
insignificant
 Pentosans – acted upon by bacteria to produce
organic acids, alcohols and carbon dioxide

Starch – the most common dietary form of

carbohydrate
- Composed of:
o Amylose – linear pattern of glucose  Beta-amylases (alpha-1,4 glucan
linked by α-1,4 glycosidic bonds maltohydrolase)
o Amylopectin – branched polymer; • E.g barley malt
glucose linked by α-1,4 glycosidic bonds • Dextrinogenic amylase
with branching via α-1,6 – linkages • Breaks β-1,4 glycosidic linkage
• Not found in human GIT
• Equivalent enzyme is CELLULASE ; found
among ruminants or grassgrazing animals
with large cecum (e.g. cows, carabaos,
horses, goats)
• Effects the successive removal of
disaccharides (maltose units) from the non-
reducing ends
o The enzyme cannot hydrolyze the
alpha-1,6 bonds and the reaction stops
at this point.
o The fragment which remains is called
DEXTRIN or LIMIT DEXTRIN
A. MOUTH/BUCCAL CAVITY
- First area where carbohydrates undergo B. STOMACH
digestion - Little digestion of polysaccharide
- Contains Ptyalin or Salivary Amylase - Gastric juice has no carbohydrate-splitting
enzyme
Starch hydrolysis
- Salivary amylase is inactivated by pepsin
- Hydrolysis of starch either by the action
- Fructosans are broken down by HCl
of amylolytic enzyme or by acid gives rise
to split fragments with simultaneous
C. SMALL INTESTINES
production of maltose. In the presence of
- Digestion of polysaccharides & disaccharides
maltase, maltose is converted to glucose.
is complete
In acid, however, the final product is
- pancreatic amylase and disaccharidases
glucose
hydrolyze CHO into monosaccharides
BIOCHEMSITRY
- CHO absorbed in the jejunum in the form- Pentoses
of 9%
monosaccharides
- Undigestible CHO due to β-1,4 glycosidic * The absorbed monosaccharides are brought
bonds to the 3 big veins of the GIT. 1 fuses with 2, 2
- Examples: high-fiber fruits and vegetables fuses with 3 to form a big portal vein to
which contain Cellulose, hemicelluloses and transport monosaccharides into the LIVER
Pectin
VEINS of the GIT
- In the L.I., these form bulk or roughage which
swells with water, promoting peristalsis 1.
andSuperior mesenteric veins
easier evacuation of stool. 2. Splenic veins
3. Inferior mesenteric veins

Factors affecting absorption of CHO

1. Glucose decreases the absorption rate of
ABSORPTION galactose and xylose
- Pores of the mucosa through which diffusion occurs 2. Galactose decreases the absorption rate of
are impermeable to water soluble solutes with MW > glucose but no effect on xylose
than 100. 3. Phlorhizin (structurally similar to glucose)
- Simple Diffusion: pentose inhibits glucose transport a. Causes phlorhizin
- Facilitated Diffusion: involves a carrier protein or glycosuria
lipoprotein (fructose and mannose) 4. Vitamins: thyroxine and the B complex vitamins
- Active Transport: glucose and galactose (thiamine, pyridoxine, pantothenic acid) promote
- Secondary active transport absorption of hexoses
- A carrier transport is present in the brush border of 5. Hyperglycemia – increased sugar levels in the
the epithelial cell. blood
o The carrier has a receptor site for both a. Results when the liver cannot completely
glucose and sodium. clear the CHO from the blood and it goes to
▪ It will not transport glucose to the inside the systemic circulation
of the cell if the receptor sites for both b. Happens after 1 hour of ingesting large
glucose and sodium ion are not amounts of CHO
simultaneously filled. c. Goes back to normal after 2 hours or even
▪ The energy to cause the movement of the to fasting level
carrier from the exterior of the membrane d. This is the basis for the glucose tolerance
to the interior is derived from the test
difference in sodium concentration
between the outside and the inside. As 5. Sprue – passage of
sodium diffuses to the inside of the cell, it carbohydrates (and lipids) in
drags the carrier and glucose along with intestinal mucosal cells is
it, thus providing the energy for the inhibited a. Oral administration
transport of glucose. of CHO do not follow the
normal GTT but IV
Relative rate of transport of monosaccharides administration follow normal
(glucose as standard) GTT curve b. Poisoning the
- Galactose 110% GIT with iodoacetate and
- Glucose 100% phlorhizin produces the same
- Fructose 43%
- Mannose 19%
BIOCHEMSITRY
- Lactose intolerance/ lactase deficiency
syndrome
- Sucrose intolerance
- a-dextrinase deficiency (infants and children)
*Incomplete digestion of amylopectin,
maltose, sucrose or lactose leads to
bacterial decomposition in the LI
o Incomplete digestion of amylopectin,
maltose, sucrose or lactose leads to
bacterial decomposition in the LI
- Leads to the production of glucose and other
monosaccharides + organic acids and gases
- Produces flatus and diarrhea

Blood Glucose
NV = 80 – 100 mg%
FBS = 70 – 100 mg%
Postprandial = 130 – 160 mg%

Carbohydrate metabolism
Glucose is the universal fuel of human cells. Every
- The CNS is dependent on these normal values
cell type in the human body is able to generate
- Glucose is the major energy source that crosses the
adenosine triphosphate (ATP) from glycolysis, the
blood-brain barrier
pathway in which glucose is oxidized and cleaved
- If glucose falls to 25 mg%:
to form pyruvate. The importance of glycolysis in
our fuel economy is related to the availability of o Person becomes stuporous
glucose in the blood, as well as the ability of o After 10 minutes = coma
glycolysis to generate ATP in both the presence or o Irreversible after 30 minutes
absence of oxygen. Glucose is the major sugar in
- The muscle can derive energy from ketone bodies
our diet and the sugar that circulates in the blood
- The myocardium take up fatty acids and lactic acid
to ensure that all cells have a continuous fuel
from blood and use as source of energy
supply. The brain uses glucose almost exclusively
o The heart is insensitive to fluctuations of blood
as fuel.
sugar levels
Metabolic intermediates *Physiological and hormonal mechanisms keeps
- Used in other metabolic processes in the cell blood sugar levels at 60 mg% even in
- Multiple step pathway helps the cell to handle prolonged starvation
metabolic energy efficiently
- The quantity of energy released in each step is Factors that lower blood glucose levels
small enough to be handled by the cell 1. Glycogenesis – transformation of glucose into
glycogen
* All cellular processes are interrelated 2. Glycolysis – utilization of glucose for heat and
energy
Claude Bernard 3. Lipogenesis – conversion of glucose to fats
- Demonstrated that blood sugar levels vary in 4. Formation of certain amino acids
the different areas of the circulation 5. Glucosuria – excretion of glucose in the urine
o Portal blood – less sugar
o Hepatic vein – more sugar Hormone that lowers blood glucose levels
▪ There must be some regulating mechanism 1. Insulin
in the liver - Hormone secreted by B-cells of islets of
Langerhans in pancreas
CHO malabsorption/dissacharide intolerance
- Produces hypoglycemic effect by:
BIOCHEMSITRY
 Increasing glycogenesis - 11-oxysteroid groups – with anti-insulin activity
 Decreasing gluconeogenesis o Corticosterone
o (Compound B)
o 11-dehydro-17-hydroxycorticosterone
Increasing glucose utilization by
tissues (compound E, cortisone)
o 17-hydroxycorticosterone (compound F,
 Promoting lipogenesis
hydroxycortison, cortisol)
- Facilitates entrance of glucose in the cell where
it is immediately phosphorylated to be converted
4. Thyroxine or tetraiodothyronine
to energy to undergo glycolysis
- Increase absorption of hexoses from intestines
- Deficient insulin diminishes entrance of glucose
- Stimulates liver glycogenolysis
in the cell, thus less phosphorylation
- Glucose remains in the blood producing
5. Glucagon
hyperglycemia - If its concentration exceeds the
– from A cells of islets of Langerhans
renal threshold, it is excreted in the urine
- promotes hepatic glycogenolysis and
- This is known clinically as diabetes mellitus
gluconeogenesis
*To cover energy requirements: (during
hypoglycemic state)
6. Epinephrine and norepinephrine
(catecholamines)
1. Gluconeogenesis
- promotes both liver and skeletal glycogenolysis
- Production of glucose from non-
- physical or emotional stress cause increase
carbohydrate sources like proteins will
production of epinephrine and an immediate
increase nitrogen excretion in the urine.
production of glucose for energy
Wasting of body tissues
7. Somatostatin: (delta cells)
- It inhibits secretion of insulin and glucagon
2. Lipolysis
- also inhibits the release of GH
- Breakdown of fats
- Happens when the patient losses 100 – 200 g
8. Growth hormone / Somatotrophic hormone:
of glucose per day
(anterior pituitary gland)
- Leads to ketonemia
- antagonist to insulin; - it stimulates lipolysis
o When aceto acetyl CoA is produced in excess
during catabolism of fats for the capacity of the
9. Human Placental Lactogen (hPL)/Human
extrahepatic tissues to utilize, they accumulate
Chorionic Somatomammotropin
in the blood.
- with anti-insulin activity
- Complication - gestational diabetes
o Renal excretion of acetoacetic acid and B-
hydroxybutyric acid in the form of Na salts Immediate Effects in Increased BGl
o The blood is depleted of Na producing acidosis - Physiologic increase in the uptake of glucose by
o Large quantity of fluid is lost = dehydration liver and brain cells
- Release of insulin
- Increase uptake of glucose by peripheral tissues
Factors that increase blood glucose level - Inhibition of glucagon release
1. Glycogenolysis - Conversion of liver
glycogen into blood glucose Fate of Glucose
2. Gluconeogenesis - Synthesis of blood 1. Blood glucose (also called physiologic sugar)
glucose from non-CHO sources 2. Glycogen - stored glucose
3. Alpha-keto acids – part of non-essential amino
acids
Hormones that increase blood Glucose 4. Constituent of body structures
1. ACTH 5. Lipogenesis – produce adipose fat (from
glycerol)
2. TSH 6. Pyruvate – key metabolite in the Kreb’s cycle
Both ACT and TSH have diabetogenic effect

3. Adrenal cortical hormones

BIOCHEMSITRY
o End product: glyceraldehyde-3-PO4
- Conversion of glyceraldehyde-3-PO4 into lactic
acid, with energy yield conserved as ATP

I. Phosphorylation and Cleavage of Glucose

1. Glucose is phosphorylated to glucose-6-PO4
- Enzyme: Hexokinase and Glucokinase
o Hexokinase
▪ Also catalyzes phosphorylation of fructose,
mannose and glucosamine aside from
glucose
▪ Has higher affinity for aldohexoses than
ketohexoses
o Glucokinase
Glucose – 6 – PO4 (product after ▪ Phosphorylate only glucose
phosphorylation of glucose) ▪ Has lower affinity for glucose than hexokinase
- Udergo glycolysis (anaerobic) via EMP
- Enter Kreb’s cycle (aerobic) 2. Conversion of glucose-6-PO4 to fructose-6-
- Enter HMS (Hexose Monophosphate shunt) PO4
- Converted to glycogen - Enzyme: phosphoglucoisomerase
- Converted to fat
- Excreted through the urine
GLYCOLYSIS - Catabolism of glucose 3. Phosphorylation of fructose-6-PO4 to fructose-
1,6 diPO4
2 types - Enzyme: phosphofructokinase
1. Aerobic - In the presence of oxygen - A second molecule of ATP is invested to
- Produces pyruvic acid, carbon dioxide, water and phosphorylate in position 1
heat - The reaction indicates that it is essentially
2. Anaerobic - In the absence of oxygen irreversible in the cell
- Produces lactic acid and energy
4. Cleavage of fructose 1,6 diPO4 to
2 Major Pathways: glyceraldehyder-3-PO4 and dihydroxyacetone
Embden-Meyerhof pathway (EMP) PO4
– Also known as the glycolytic pathway - Enzyme: Aldolase
- Glucose is broken down to pyruvic and lactic acid in
the absence of oxygen (anaerobic) 5. The interconversion of triose PO4
- Only glyceraldehyde-3-PO4 can be degraded in the
Kreb’s Cycle further reaction of glycolysis
- Acetyl CoA (EMP)is split to carbon dioxide, water - DHA-PO4 is reversibly converted to glyceraldehyde-3-
and energy in ATP PO4
- This is the final common pathway for glucose, fatty - Enzyme: Triose PO4 isomerase
acids and certain amino acids - One molecule of glucose forms 2-glyceraldehyde-3-
- 90% of energy is derived from this pathway PO4

II. Conversion of Glyceraldehyde-3-PO4 into lactic

EMBDEN-MEYERHOF PATHWAY (EMP) acid
- Also known as the glycolytic pathway 1. Oxidation of glyceraldehyde-3-PO4 to 1,3
- Glucose is broken down to pyruvic and lactic acid in diphosphoglycerate
the absence of oxygen (anaerobic) Enzyme: glyceraldehyde dehydrogenase
- The central pathway for glucose catabolism
2. Transfer of one phosphate group of 1,3
diphosphoglyceric acid to ADP forming 3-
2 Stages phosphoglyceric acid and ATP
- Phosphorylation and cleavage of glucose Enzyme: phosphoglyceric acid kinase
BIOCHEMSITRY
3. Conversion of 3-phosphoglyceric acid to 2-
phosphoglyceric acid
Enzyme: phosphoglucomutase
4. Dehydration of 2-phosphoglyceric acid to
phosphoenol pyruvic acid
Enzyme: enolase
5. Transfer of phosphate group from
phosphopyruvic acid to ADP
Enzyme: pyruvic acid phosphokinase
DISEASES ASSOCIATED WITH IMPAIRED
6. Reduction of pyruvic acid to lactic acid
GLYCOLYSIS
Enzyme: lactic acid dehydrogenase
- Lactic acid is the end product ofHEXOKINASE
glycolytic DEFICIENCY
sequence under anaerobic conditions- and In lactic
patients with inherited defects of hexokinase
acid is a blind alley in metabolism activity, the red blood cells contain low concentration
- Lactic acid once formed is not further of the glycolytic intermediates, including the
utilized
precursor,
- Fatigue and rigor of muscle fibers is in part due 2,3- Diphosphoglycerate
to acidification by lactic acid - In consequence, the Hemoglobin of these patients
has an abnormally high oxygen affinity
* Net synthesis of 2 molecules of ATP for every
- The oxygen saturation curves of RBCs from a
molecule of glucose converted to lactic acid
patient with hexokinase deficiency are shifted from the
left, which indicates that Oxygen is less available for
the tissues
Inhibition of Anaerobic Glycolysis by
PYRUVATE KINASE DEFICIENCY (Hemolytic
Oxygen (Pasteur Effect)
Anemia)
- Rate of glycolysis was based on the
- All RBCs are completely dependent upon
disappearance of glucose and accumulation of
glycolytic activity for ATP production
lactic acid
- Failure of the pyruvate kinase reaction drastically
- The rate of glycolysis is slowed in the presence of
impedes the production of ATP
Oxygen
- Inadequate production of ATP reduces the
- Oxygen: lactic acid CO2 and H2O
activity of the Na+ and K+ stimulated Adenosine
- Energy released: utilized to resynthesize glucose
Triphosphatase ion pump, which maintains the
from remaining lactic acid
shape of the RBC membrane. In consequence, the
- Net Effect:
cells swell and lyse, and this excess RBC
o Decrease in the total consumption of glucose
destruction results in hemolytic anemia
o Less accumulation of lactic acid
LACTIC ACIDOSIS
- Blood levels of Lactic acid are normally less than
1.2mM. In lactic acidosis, the values for blood
lactate may be 5.0 mM or more
- The high concentration of lactate results in
lowered blood pH and bicarbonate levels
- High blood lactate levels can result from
increased formation or decreased utilization of
lactate
- A common cause of hyperlactidemia is ANOXIA,
in which:
o The formation of lactate is increased,
because the shortage of oxygen reduces
mithochondrial production of ATP with the
consequent activation of PFK, causing
increased glycolysis and lactate production
BIOCHEMSITRY
o The use of lactate by the tissues is reduced ▪ also known as the citric acid cycle, or the
because the use of lactate as an energy source Krebs cycle, after Hans Adolf Krebs who
requires oxygen identified the cycle.
- Tissue Anoxia may occur in shock and other ▪ a series of chemical reactions of central
conditions that impair blood flow, in respiratory importance in all living cells that use
disorders, and in severe anemia. oxygen as part of cellular respiration.
FATE OF PYRUVATE ▪ part of a metabolic pathway involved in
- Reconverted to glucose-6-phosphate the chemical conversion of carbohydrates,
- Combine with NH3 to form alanine fats and proteins into carbon dioxide and
- May combine with CO2 to form oxaloacetic acid water to generate a form of usable energy.
- May be oxidatively decarboxylated and combine
with CoA to form acetyl CoA o Electron Transport Chain and Oxidative
Phosphorylation
FATE OF LACTATE
▪ produces ATP through chemiosmotic
- Circulated back to the liver and converted to
phosphorylation.
glycogen
- Converted to pyruvate to enter Kreb’s cycle
TRICARBOXYLIC ACID CYCLE/CAC/KREB’S
CYCLE
- Final common pathway of oxidative catabolism
of all fuel molecules in aerobic cells
(mitochondrial matrix)
- Greater amount of energy is released when
glucose is completely oxidized to CO2 and H2O

o This is because the product of glycolysis,

the lactic acid is still complex while the
product of respiration, CO2 is a smaller
molecule whose carbon atom is completely
oxidized.
o H ion is then fed into the respiratory chain,
a series of electron carriers
- Also known as Kreb’s cyle, citric acid cycle
- First described by Hans Adolf Kreb (1900-
1981)
- Occurs in the mitochondria
- Starts with acetyl group from
carbohydrates, lipids and amino acids
- Common pathway of oxidative catabolism
A simplified Diagram showing acetyl-CoA of all fuel molecules in aerobic cells
is at the hub of protein, carbohydrate and
fat metabolism - AMPHIBOLIC pathway – involves both anabolic
& catabolic processes
Aerobic Respiration o ANABOLIC process – provides routes for
- process where the pyruvate produced in the synthesis of biosynthetic precursors (e.g.
glycolysis undergoes further breakdown. α-Ketoglutarate, Oxaloacetate, Succinyl CoA)
- requires oxygen and yields much more o CATABOLIC process – degradation of 2-C
energy than glycolysis. acetyl residues from CHO, fatty acids & amino
- Two processes: acids
o Krebs cycle
BIOCHEMSITRY
- Starts with acetyl group from carbohydrates,
Step 2: Citrate is rearranged to form isocitrate with
lipids and amino acids the temporary formation of cisaconitate
- Common pathway of oxidative catabolism -Enzyme:
of all Aconitase
fuel molecules in aerobic cells

Pyruvate
- Link between EMP and TCA
- Does not directly enter TCA
- Converted to acetyl CoA

Conversion of pyruvic acid to acetyl CoA 3

steps involved
1. Decarboxylation o Removal of C from Step pyruvic3: Decarboxylation - Isocitrate (6-C) is
acid and released as CO2 oxidized and CO2 is removed to produce α-
2. Oxidation o Removal of H+ and accepted by
ketoglutarate (5-C)
NAD+
*All dehydrogenase reactions make NADH or
3. Condensation of acetic acid with CoA to produce
acetyl CoA FADH2

2 steps
o Oxidative decarboxylation of aketoglutaric acid to succinyl
CoA
▪ Enzyme: a-ketoglutaric acid synthetase
o Succinyl CoA undergoes loss of its CoA
▪ Enzyme: succinyl thiokinase or succinyl CoA synthetase

Individual Reactions in the TCA

Step 1:
Condensation - Transfer of 2-C acetyl group to the Step 5: CoA is removed from succinyl CoA to
oxaloacetate a 4-C compound to form 6-C citrate produce succinate
- Enzyme: Citric acid synthetase o Regulatory enzyme - Coupled with the synthesis of GTP
o Inhibited by ATP - GTP is very similar to ATP
- Methyl group of acetyl CoA condenses with the –GTP donates its terminal phosphate group to ADP
carbonyl atom of oxaloacetic acid with hydrolysis to form ATP
thioester bond and formation of free CoA

Step 6: Oxidation
Citrate - Oxidation of succinic acid to fumaric acid
- If it accumulates in the mitochondria o Inhibitory - Enzyme: flavoprotein succinate dehydrogenase (w/
to phosphofructokinase FAD)
o Slows glucose metabolism by way of - FADH2 can donate electrons to various
glycolysis s electron acceptors
- If it accumulates in the cytoplasm
o Results in citrate cleavage thru citrate lyase
BIOCHEMSITRY
2 NADH = 6ATP (or 4 ATP’s)
Kreb’s cycle
8 NADH (1 NADH will produce 3 ATP’s)
2 FADH2 (1 FADH2 will produce 2 ATP’s)
2 ATP’s = 2 ATP
Electron transport chain
Step 7: Hydration 3 x 8 NADH = 24 ATP’s
- Water is added to fumarate (4-C) producing malate2 x 2 FADH2 = 4 ATP’s
(4-C)
- Enzyme: fumarase Total: 36 or 38 ATP’s/glucose molecule
- This reaction involves addition of water across the
double bond

The Kreb’s Cycle

Redox CoEnzymes
Step 8: Oxidation 1. NAD+ - Nicotinamide adenine dinucleotide
- Malate is oxidized to form oxaloacetate 2. NADH+ - Nicotinamide adenine dinucleotide
- Enzyme: malic acid dehydrogenase (w/ (reduced)
NAD) - This reaction makes NADH 3. FAD+ - Flavine adenine dinucleotide
- It regenerates oxaloacetate for another
round. - NAD+ and NADP+ are both from the vitamin niacin
- FAD+ is from the vitamin riboflavin
- For NAD+ and NADP+, nicotinamide is the active
center, it recieves H
– For FAD+, flavin is the active site
- Main function: carry electrons to the mitochondrial
electron transport chain

* As the CoEnzymes are oxidized, molecular oxygen

is reduced

Oxygen metabolism
Oxygen - Final receptacle for electrons in the
mitochondrial electron transport system - Too
much of it is dangerous to life - Normal reaction:

Overall glucose tally

*Water is a safe product
Glycolysis
*Other reduced products of oxygen are dangerous
2 ATP in 4 ATP = 2 ATP’s
BIOCHEMSITRY
- Process that directly uses energy from redox
ROS – reactive oxygen species reactions to form ATP
- Can destroy many vital cell molecules
- Occurs in the mitochondria
- Depends on the electron transport system
1. H2O2 – produced when redox reactions
- Needs oxygen to proceed, thus, aerobic
involve 2e

THE ELECTRON TRANSPORT CHAIN

2. O2-1 – formed when redox reactions involve1. The final common pathway in aerobic cells by
only 1e3. OH – hydroxyl radical - neutral OH which
thatelectrons derived from various substrates
can react with almost anything in the cell are transferred to oxygen
2. many substrates are oxidized by enzymes that
ROS toxicity use NAD+ or FAD+ as electron acceptor cofactors
- Large bursts of ROS
o When skin is exposed to UV light = Cancer
The Mitochondrial Structure
o Stroke and heart attack 3. Outer membrane – permeable to most small
molecules
▪ Ischemia – limited oxygen supply (may
4. Intermembrane
be space – presents no barrier to
due to blood clot) metabolites
▪ Reperfusion – restoration of blood5.supply
Inner membrane – highly selective; provides
that cells cannot handle = ROS burststransport systems for the following substances:
o ATP, ADP & Pi
Defense Mechanism against ROS o Pyruvate, succinate, αketoglutarate,
- Superoxide dismutase – destroys superoxide to
malate & citrate
form 1 hydrogen peroxide
o Cytidine and GTP

- Catalase – can convert H2O2 to H2O

6. Note: The enzymes of the ETC & oxidative
phosphorylation, including Succinate
High Energy Phosphate Bonds dehydrogenase are found in the inner
mitochondrial membrane
- Phosphoanhydride bond
7.Matrix – contains the enzymes of the Kreb’s
cycle (except Succinate dehydrogenase),
enzymes of β-oxidation of fatty acids and other
miscellaneous enzyme systems
▪ Both phosphate groups are negative radicals ▪
Repulsive force acts like spring
ORGANIZATION OF THE ELECTRON
▪ Release of energy is through simple hydrolysis
TRANSPORT CHAIN

2 Types of Phosphorylation
Substrate level phosphorylation
- Process whereby energy derived from oxidation
is used to form high energy PO4 bonds on various
biochemical molecules
- Examples: phosphoenol pyruvate, 1,3-
diphosphoglycerate, phosphocreatine
- Phosphorylated substrate transfers phosphate to
ADP for form ATP 8. The cytochromes and the Fe-S protein
- Happens under anaerobic conditions centers are one-electron carriers.
9. NADH, FADH2 and Q are two-electron
Oxidative phosphorylation carriers
BIOCHEMSITRY
10. For every pair of electrons w/c come fromNADH passes along 2 electrons to
NADH, 3 moles of ATP are generated (1) FMN
11. For every pair of electrons w/c come from(2) iron-sulfur protein (FeS)
FADH2, 2 moles of ATP are generated (3) to coenzyme Q.

SOURCES OF ELECTRONS - The net effect of these reactions are to

12. NADH is derived from NAD+-linked regenerate coenzyme NAD+.
dehydrogenases, including: - This regeneration of reactants produces a
o Isocitrate, α-ketoglutarate, and malate cycling effect.
dehydrogenases of the TCA cycle - The NAD+ is ready to react further with
o Pyruvate dehydrogenase metabolites in the citric acid cycle.
o L-3-Hydroxyacyl CoA dehydrogenase
of fatty acid oxidation (4) Coenzyme Q picks up an additional 2
o Miscellaneous NAD+-linked hydrogen ions to make CoQH2
dehydrogenase

13. FADH2 is derived from FAD-linked *CoQH2 is soluble in the lipid membrane
dehydrogenases, including: and can move through the membrane to
o Succinate dehydrogenase of the TCA come into contact with enzyme complex
cycle 3.
o FAD-linked dehydrogenase of the α-
glycerophosphate shuttle (5) Coenzyme QH2 carrying an extra 2
o Acyl CoA dehydrogenase of fatty acid electrons and 2 hydrogen ions starts a
oxidation cascade of events through enzyme complex
o Miscellaneous FAD-linked 3, also known as cytochrome reductase b.
dehydrogenases (Enzyme complex 3)
- Cytochromes are very similar to the structure
The electron transport chain is threefold: of myoglobin or hemoglobin.
1) to pass along 2H+ ions and 2e- to eventually - The significant feature is the heme structure
react with oxygen; containing the iron ions, initially in the +3 state and
2) to conserve energy by forming three ATP's; changed to the +2 state by the addition of an
and electron.
3) to regenerate the coenzymes back to their
original form as oxidizing agents. (6) The CoQH2 passes along the 2 electrons to (a)
cytochrome b1 heme (b) b2 heme , (c)iron-sulfur
Initiation of Electron Transport Chain: protein, (d)cytochrome c1, (e)finally to cytochrome c.
14. NADH interacts with the first complex 1
enzyme, known as NADH reductase. (7) In the meantime the 2 hydrogen ions are
15. This complex 1 contains a coenzyme flavin channeled to the interspace of the mitochondria for
mononucleotide (FMN) which is similar to FAD ultimate conversion into ATP.
16. 2H+ = 1 ATP

*NADH + H+ enter the enzyme complex and

pass along the 2 hydrogen ions to an
interspace in the mitochondria.

*These hydrogen ions, acting as a pump, are

utilized by ATP synthetase to produce an ATP
for every two hydrogen ions produced
complexes 1, 3, 4 act in this manner to produce
2 hydrogen ions each, and thus will produce 3
ATP for every use of the complete electron
transport chain
BIOCHEMSITRY