Enzymes and Vitamins Subclasses of Oxidoreductases:

Enzymes- a compound, usually protein, that acts as a  Oxidases- oxidation of substrate.

catalyst for biochemical reaction. C
R→P  Reductases- reduction of substrate.
 Dehydrogenases- introduction of double bond by
Catalyst- accelerate rates of chemical reactions but at removal of two H atoms from a substrate, with H
the end of the reaction have undergone no change. being accepted by a coenzyme

Enzyme Structure: 2. Transferases- catalyze transfer of a group from one

 Simple enzyme- only protein (amino acid chain) molecule to another.
 Conjugated enzyme- has a non-protein part in Ex: Fructose 6-phosphate ATP -3 Phosphate group
addition to a protein part. to to
ATP -2 Phosphate group
 Apoenzyme- protein part of a conjugated enzyme. Fructose 1, 6-biphosphate
 Cofactor
-non-protein pat of conjugated enzyme. Subclasses of Transferases:
-essential to the enzyme’s catalytic activity; a metal  Transaminase- transfer of amino group between
ion or a coenzyme. substrates.
 Holoenzyme- the biochemically active conjugated  Kinases- transfer of phosphate group between
enzyme produced from apoenzyme and cofactor. substrates.
Ex: Glucose
Enzyme Naming process: to
1. suffix -ase Glucose - 6 - Phosphate
-exception: pepsin, chymotrypsin, trypsin
2. type of reaction catalyzed by enzyme is often noted 3. Hydrolases- catalyze the hydrolysis of substances –
with a prefix. the breaking of bonds with addition of water.
H2 O
Ex: Oxidase- catalyzes oxidation reaction
Hydrolase- catalyzes hydrolysis reaction Subclasses of Hydrolases:
(nagpuputol ng bonds)  Lipases- hydrolysis in ester linkages in lipids.
reactant
 Proteases- hydrolysis of amides linkages in protein.
3. the identity of substrate is often noted in addition to  Nucleases- hydrolysis of sugar-phosphate ester
the type of reaction. bond in carbohydrates.
Ex: Glucose oxidase  Carbohydrase- hydrolysis of glycosidic bonds on
Pyruvate carboxylate carbohydrates.
Succinate dehydrogenase  Phosphatase- hydrolysis of phosphate ester bond.
“lein”- to break
Classification of Enzymes: 4. Lyases- catalyze the addition of a molecule such as
1. Oxidoreductases H2O or CO2 to a double bond or the reverse reaction in
-catalyzes oxidation-reduction reactions of substitute which a molecule is eliminated to leave a double bond.
molecules, addition or removal of oxygen or hydrogen. (breaks double bond)

 Oxidation (positive) Ex: Fumarate (nawaal si double bond)

-loss of electrons.
-increase in oxidation number. Subclasses of Lysases:
reaction
 Dehydratases- removal of H2O from a substrate.
 Reduction (negative)  Decarboxylases- removal of CO2 from a substrate.
-gain of electrons.  Deaminases- removal of NH3 from a substrate.
-decrease in oxidation number.  Hydrates- addition of H2O to a substrate.
 Enzyme
5. Isomerases- catalyze the isomerization -substrate complex
(rearrangement of atoms) of a substrate in reactions -the intermeasate reaction species
that have but 1 substrate and 1 product.
 Active site
Ex: Dihydroxyacetone -pocket in an enzyme with the specific shape and
Same number but diff
Phosphate arrangement chemical make up necessary to bind a substrate.
-place where enzyme attaches.
Subclasses of Isomerases:
 Racemases- conversion of D-isomer to L-isomer vice  Substrate
versa. -reactant in an enzyme catalyzed reaction.
 Mutase- transfer of functional group from one -are shaped to fit into the active site if the active
position to another in the same molecule. site is the wrong shape the reactants won't fit.

6. Ligases  Product- result of reaction (released from the active

-Latin ligare “to tie together” site)
-catalyze the bonding together of 2 substrate molecules.
(with ATP)

Subclasses of Ligases:
 Synthase- formation of new bond between 2
substrates, with participation of ATP.
 Carboxylase- formation of new bond between a
substrate and CO2 with participation of ATP.
Enzyme-Substrate Complex- is the intermediate
Ex: Pyruvate to Oxalacetate reaction species that is formed when a substrate binds
to the active site of an enzyme

Models of Enzyme Action:

1. Lock-and-Key Model- the rigid enzyme and substrate
have matching shapes. (1 shape)

2. Induced fit- the flexible enzyme changes shape to

match the substrate.

3. Specificity- limitation of the activity of an enzyme to a

specific substrate, specific reaction, or a specific type of
reaction.

 Absolute specificity- the enzyme will catalyze

only 1 reaction.

 Group specificity- the enzyme will act only in a

specific functional group.

 Linkage specificity- the enzyme will act on a

particular type of chemical bond.
  Stereochemical specificity- the enzyme will only Extremophile- is a microorganism that thrives in
act on a particular stereoisomer. extreme environments, environment in which humans,
most ither forms of life could not survive.

Turn over number for some enzymes- maximum

Extremophiles types:
number of substrate molecules acted upon by 1
 Acidophiles- optimal growth at pH levels of 3.0
molecule of enzyme per unit time.
below.
 Alkaliphiles- optimal growth at pH levels of 9.0
Coenzyme- organic molecule that acts as an enzyme
above.
cofactor.
 Halophiles- grow in high salinity.
 Hyperthermophiles- grow at temperature between
How enzyme works:
80 °C and 121 °C.
Enzyme act as catalysis because of their ability to:
 Piezophiles- grow in high hydrostatic pressure
1. Bring substrates and catalysis sites together.
 Xerophiles- grow in extremely dry conditions.
(proximity effect)
 Cryophiles- grow at temperature of 15 °C or lower.
2. Hold substrates at exact distance and in the exact
orientation necessary for reaction.
Extremozyme- microbial enzyme active at conditions
(orientation effect)
that would inactivate human enzymes.
3 provide acidic, basic, or other types of groups required
 Activation- process that initiates or increases the
for catalysis.
action of an enzyme.
(catalytic effect)
 Inhibition- process that slows or stops the action of
4. Lower the energy barrier by inducing strain in bonds
an enzyme.
in the substrate molecule.
(Energy effect)
Feedback control- regulation of an enzyme’s activity by
the product of a reaction later in pathway.
Enzyme Activity- is a measure of the rate at which an
enzyme converts substrate to products in a biological
Allosteric control- binding of a molecule (an allosteric
reaction.
regulator or effector) at one site on a protein affects the
binding of another molecule at a different site.
Factors that affect enzyme:
 Effect of Temperature on Enzyme activity- reaction
Positive (+) – activates Allosteric regulator- substrates
role increases with increasing temperature until a
Negative (-) – deactivates can enter
temperature is reached at which the enzyme begins
Allosteric regulator- substrate
to denature; then the rate decreases rapidly.
cannot enter (will close)
Allosteric enzyme
 Effect of pH on Enzyme activity
-an enzyme whose activity is controlled by the binding
-pepsin, which initiates protein digestion in highly
of an activator or inhibitor at a location other than the
acidic environment of the stomach.
active site.
-chymotrypsin, an enzyme that aids digestion of
-have quaternary structure, composed of 2 or more
proteins in the small intestines.
protein subunits.
-have 2 kinds of binding sites, those for substrate and
Extreme temperature = denatured enzyme will not work
those for regulators.
-active and regulatory binding sites are distinct from
 Substrate concentration- if the substrate
each other in both location and shape.
concentration doubles, the rule doubles (a directly
-binding of a molecule at the regulatory site causes
proportional relationship.
changes in the overall 3-dimensional structure of the
enzyme, including structural changes at the active site.
 Enzyme concentration- if the enzyme concentration
double, the rate doubles. (a directly proportional
relationship.
The inhibition of an enzyme can be:  ACE inhibitors- block the action of ACE.
 Reversible inhibition- the inhibitor can leave, If ACE inhibitor does not block = not harmful to the body
restoring the enzyme to its uninhibited level of
activity.  ACE- converts inactive decapeptide zymogens to
 Irreversible inhibition- the inhibitor remains active octapeptide.
permanently bound and the enzyme is permanently
inhibited. ACE Inhibitor medication
-blocks the action of ACE.
Enzyme inhibition- a substance that slows or stops the -effect is a lower blood pressure than if the zymogen
normal catalytic function of an enzyme by binding to it. activation had occurred. (ex: Lisinopril)

3 models by which inhibition take place: Sulfa drugs

1. Competitive enzyme inhibitive- molecule resembling -1st antibiotic in medical field.
the substrate binds to the active site and temporarily -antibiotic is a substance that kills bacteria or inhibits
prevents substrates from occupying it, thus blocking the their growth.
reaction. (may nag-uunahan pumasok) -Penicillin inhibits transpeptidase, an ezyme that
catalyzes formation of peptide-cross links between
polysaccharide strands in bacterial cell wall.
2. Noncompetitive enzyme inhibitive- a molecule that
binds to a site on an enzyme is not active site. The Medical uses of Enzymes:
normal substrate still occupies the active site, but the -enzymes can be used to diagnose and treatment of
enzyme cannot catalyze the reaction due to the disease.
presence of the inhibitor. (may iba pang papasukan) -the use of tissue plasminogen activator (TPA) in treating
heart attack.
-when activated, this enzyme dissolves blood clots in
3. Irreversible enzyme inhibitive- a molecule forms a the heart and often provides immediate relief
covalent bond to a part of the active site, permanently
preventing substrates from occupying it. (permanent) Vitamins and Minerals
Vitamin
-an organic molecule, essential in trace amounts that
Prescription drugs that inhibit enzyme activity: must not be obtained in diet because it is not
ACE (Angiotensin-Converting Enzyme.) synthesized in the body.
-octapeptide hormone involved in blood pressure -solubility characteristics divide the vitamins into
regulation. 2 major classes:
-increase blood pressure by narrowing blood vessels.  Water-soluble vitamins
 Fat-soluble vitamins (13 Vitamins)
Angiotensinogen (a zymogen)
Water-soluble vitamins Fat-soluble vitamins
1. Vitamin C 1. Vitamin A
2. Thiamin 2. Vitamin D
Angiotensin I- a decapeptide (10)
3. Riboflavin 3. Vitamin E
Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Lieu
4. Niacin 4. Vitamin K
angiotensin I to angiotensin II
5. Pantothenic acid
– reversible competition
6. Vitamin B2
Angiotensin II- increase blood pressure, narrows vessel. 7. Biotin
Asp-Arg-Val-Tyr-Ile-His-Pro-Phe 8. Folate
9. Vitamin B12
 Water-soluble vitamins:
1. Vitamin C (Ascorbic Acid) 4. Vitamin B3 (Niacin)
-has simplest structure and exist in 2 forms in the -occurs in food in 2 different, but similar forms: nicotinic
human body: L-ascorbic acid (reduced form) & acid and nicotinamide.
Dehydro-L-ascorbic acid (oxidized form)
-sensitive to light, air, and temperature. Both forms convert to same coenzymes:
-an intake of 100 mg/day saturates all body tissues with  Nicotinamide adenine dinucleotide (NAD+)
the compound. -electron transport charge
 Nicotinamide adenine dinucleotide phosphate
Important biochemical functions for Vitamin C: (NADP+)
 Collagen synthesis -pentose phosphate pathway
 General antioxidant
 Synthesis of Neurotransmitters -both coenzymes are involved with oxidation-reduction
reactions in which hydrogen atoms are transferred from
2. Vitamin B1 (Thiamin) one molecule to another.
-also known as thiamin, “thio” meaning “sulfur” and
Pantothenic Acid parts:
“amine” which refers to the numerus amine groups 5. Vitamin B5 (Pantothenic Acid) pantoic acid and β-alanine
present. -“pantothen” – from everywhere.
-coenzyme form of thiamin is called thiamine -coenzyme A (CoA), contains B5 as part of its structure.
pyrophosphate (TPP), a molecule in which a -acyl carrier protein (ACP), is important in the
pyrophosphate group (2 phosphates bonded to each biosynthesis of fatty acids.
other)
-coenzyme TPP is needed in step 4 of the citric acid 6. Vitamin B6 (Pyridoxine, Pyridoxal, and Pyridoxamine)
cycle. -collective term for 3 related components:
 Decarboxylation of an a-keto acid  Pyridoxine- found in foods of plant origin
 Conversion of pyruvate to acetyl CoA  Pyridoxal and Pyridoxamine- foods of animal origin
Synthesis of ATP
Glucose 2 pyruvate (essential for CAC - Citric
Acid Cycle) -coenzymes participate in reaction where amino groups
are transferred between molecules.

7. Vitamin B7 (Biotin)
-can be obtained both from dietary intake and also via
biotin0producing bacteria (microbiota, hence the name
in large intestine
biotin)
-“free” biotin is biologically active.
-coenzyme, biotin, participates in carboxylation reaction
in which a carboxyl group is added to a molecule.

3. Vitamin B2 (Riboflavin) 8. Vitamin B9 (Folate)

-involves 3 fused 6-membraned rings. (2 of which -consists of 3 parts:
contain nitrogen with monosaccharide ribose) with the  Nitrogen- containing double-ring system (pteridine)
monosaccharide ribose attached to the middle ring.  Para-aminobenzoic acid (PABA)
-name come from its color (flavin = “yellow” in Latin)  One or more residues of the amino acid glutamate
and its ribose component.
9. Vitamin B12 (Cobalamin)
2 important Riboflavin-based enzymes exist: -an atom of the metal cobalt and numerous amino
 Flavin Adenine Dinucleotide (FAD) and Electron groups are present in the structure.
Transport Chains (oxidant) -only microorganisms can produce.
 Flavin mononucleotide (FMN) (not included in exam) -important in production of succinyl CoA.
 3. Vitamin E
Fat-soluble Vitamins: -4 forms: alpha-, beta-, delta-, and gamma-tocopherol
1. Vitamin A -is easily destroyed by exposure to excessive heat (such
4 major functions in the body: as deep frying and by oxidation.
 Vision -combines with the protein opsin to form the -body is as an antioxidant a compound that protects
visual pigment rhodopsin. other compounds from oxidation.
-in preventing the oxidation of polyunsaturated
Rhodopsin- participates in the conversion of light fatty acids in membrane lipids.
energy into nerve impulses that are sent to the -protects vitamin A from oxidation.
brain.
4. Vitamin K
 Regulating Cell Differentiation  Vitamin K1 (Phylloquinone)- major dietary form of
-(as retinoic acid) binds to protein receptors; those Vitamin K
Vitamin A-protein receptor complexes then bind to  Vitamin K2, found in animals and humans and can
regulatory regions of DNA molecules. be synthesized by bacteria.
-essential to blood-clotting process.
Cell Differentiation- is the process which immature -essential for formation of prothrombin and at least
cells change in structure and function to become 5 other proteins.
specialized cells.
~
 Maintenance of the Health of Epithelial Tissues Antioxidant- a substance that prevents oxidation by
-lack of Vitamin A (as retinoic acid causes such reacting with an oxidizing agent.
surfaces to become drier and harder than normal.
Free radicals
Epithelial tissue- covers outer body surfaces in -highly reactive molecular fragments with unpaired
addition to linking internal cavities and tubes. electrons (ex: superoxide ion, O2-)
-The body generates hundreds of substances called
 Reproduction and Growth “free radicals” when converting food to energy.
-Vitamin A participates in sperm development. -are extracted from food or breathed in from the air,
-normal fetal development during pregnancy. and some are generated by the sunlight’s action on the
skin and eyes
Retinoic Acid- form of Vitamin A that is needed and
is needed to cellular differentiation process.

2. Vitamin D 02-Chemical Messengers

exist in seversal forms:
 Vitamin D2 (Ergocalciferol)- found in foods of plant
origin
 Vitamin D3 (Cholecalciferol)-produced in the skin of
humans and animals by the actin of sunlight
(ultraviolet light)

-maintain normal blood levels of calcium ion and

phosphates ion so bones can absorb these ions.
 Endocrine system- depends on hormones, chemical Synapse- the place where the tip of a neuron and its
messengers that circulate in the bloodstream. target cell lie adjacent to each other.
BOTH regulate body chemistry that keep us in chemical balance
 Nervous system- electrical impulses in nerve cells,
triggered by neurotransmitters.

Messenger Molecules- can be hormones that arrive via

the bloodstream or neurotransmitters released by nerve
cells, such messengers ultimately connect with a target.

 Hormone- a chemical messenger secreted by cells

of the endocrine system and transported through
the bloodstream to target cells with appropriate
receptors, where it elicits a response.
 Neurotransmitter- a chemical messenger that
travels between a neuron and a neighboring neuron Acetylcholine- is a neurotransmitter responsible for the
or other target cell to transmit a nerve impulse. control of skeletal muscles. It is also widely distributed
in the brain, where it may play a role in the sleep–wake
Endocrine and Exocrine Glands:
cycle, learning, memory, and mood.
 Endocrine glands- pituitary gland, pineal gland,
parathyroid gland, pancreas, thymus, adrenal gland,
ovary and testes together with the hypothalamus of
1. A nerve impulse arrives at the presynaptic neuron.
the brain.
 Exocrine glands- sweat glands, salivary, and 2. The vesicles move to the cell membrane, fuse with
mammary glands. it, and release their acetylcholine molecules (several
thousand molecules from each vesicle).
Endocrine system 3. Acetylcholine crosses the synapse and binds to
-A system of specialized cells, tissues, and ductless receptors on the postsynaptic neuron, causing a
glands that secretes hormones and shares with the change in membrane permeability to ions.
nervous system the responsibility for maintaining
constant internal body conditions and responding to 4. The resulting change in the permeability to ions of
changes in the environment. the postsynaptic neuron initiates the nerve impulse
in that neuron.
Receptor 5. With the message delivered, acetylcholinesterase
-A molecule or portion of a molecule with which a present in the synaptic cleft catalyzes the
hormone, neurotransmitter, or other biochemically decomposition of acetylcholine:
active molecule interacts to initiate a response in a
target cell. 6. Choline is absorbed back into the presynaptic
neuron, where new acetylcholine is synthesized.
Feedback inhibition- occurs when the product of the
system shuts down or limits its operation.

COMPOSITION HORMONES
Steroids testosterone, estrogen, progesterone,
Amines melatonin, epinephrine, thyroid hormone
Peptides glucagon, oxytocin, antidiuretic hormone,
calcitonin, parathyroid hormone
Neurotransmitters Proteins growth hormone, insulin, prolactin, follicle
stimulating hormone, luteinizing hormone
 -plays a role in the brain in processes that control
movement, emotional responses, and the experiences
of pleasure and pain
Drug- any substance that alters body function when it is -cocaine blocks re-uptake of dopamine from the
introduced from an external source. synapse, and amphetamines accelerate release of
 Agonist- A substance that interacts with a receptor dopamine
to cause or prolong the receptor’s normal -Marijuana also creates an increase in dopamine levels
biochemical response. in the same brain areas
-where dopamine levels increase after administration of
heroin or cocaine
 Antagonist- A substance that blocks or inhibits the
normal biochemical response of a receptor.

1. Botulinus toxin (an antagonist)

-blocks acetylcholine release and causes botulism.
-It prevents the release of acetylcholine, frequently
causing death due to muscle paralysis.
-(marketed as Botox®) has found use in cosmetic
surgery, where carefully controlled doses of it are used
to temporarily tighten up wrinkled skin

2. Black widow spider venom (an agonist)

-releases excess acetylcholine.
-opposite reaction from that of botulism toxin, the
synapse is flooded with acetylcholine,
-resulting in muscle cramps and spasms.

3. Nicotine
-binds to acetylcholine receptors
-at low doses is a stimulant (an agonist) because it
activates acetylcholine receptors.
-At high doses, nicotine is an antagonist. It irreversibly
blocks the acetylcholine receptors.

Histamine and Antihistamine:

 Histamine
-is the neurotransmitter responsible for the
symptoms of the allergic reaction.
-It is also the chemical that causes an itchy bump
when an insect bites.

 Antihistamines- are a family of drugs that

counteract the effect of histamine because they are
histamine-receptor antagonists. They competitively
block the attachment of histamine to its receptors.

Dopamine