Chapter-9

Biomolecules
• Biomolecule are any of numerous substances that are produced by cells and living organisms.
• Biomolecules may be inorganic and organic.
Inorganic biomolecules: Minerals, gases and water
Organic biomolecules: carbohydrates, fats, proteins, nucleic acids, vitamins, etc.

Analysis of chemical composition

• Grind living tissue trichloroacetic acid (Cl3CCOOH). The thick slurry is now strained to filtrate
(acid-soluble) and retentate (acid-insoluble). The filtrate contains thousands of organic
compounds and some inorganic compounds like sulphate, phosphate.
• The acid insoluble fraction, has only four types of organic compounds i.e., proteins, nucleic
acids, polysaccharides and lipids.
• Weighs a small amount of living tissue and burnt it completely. The ash (dry weight) contains
inorganic elements.

PROTEINS
• Proteins are polypeptides. They are linear chains of amino acids linked by peptide bonds
• Each protein is a polymer of amino acids. There are about 20 different amino acids exist
naturally.
Essential; amino acids: dietary amino acid
Non-essential: synthesized inside the body
• Proteins carry out many functions in living organisms, some transport nutrients across cell
membranes, some fight infectious organisms, some are hormones, some are enzymes,
Amino acids-Each amino acid consists of Carbon (a-carbon), basic amino group (NH2), carboxylic group
(COOH), a hydrogen atom (H) and R group. Structurally amino acids differ only in the ‘R’ group.
• Zwitter ion: at specific pH an amino acid behaves as a zwitterion i.e. contains both positive and
negative charge.
• Based on the R group amino acids are classified as acidic, basic, polar, and non-polar.

Peptide bond
• The amino group of one amino acid and the carboxyl group of another amino acid combine
together with the loss of water and form a peptide bond. Many amino acids join to form
polypeptides (proteins).

Structure of proteins
CARBOHYDRATE
• Carbohydrates are polyhydroxy aldoses (e.g. glucose) or ketoses (e.g. fructose).
• General formulae is (CH2O)n
• They are made up of saccharide monomers.
• Saccharide monomers join together by glycosidic linkage.
On the basis of the number of saccharide units, the carbohydrates may be

• In a polysaccharide chain (say glycogen), the right end is called the reducing end and the left end
is called the non-reducing end.

LIPID
• Lipids are fatty, waxy, or oily compounds that are soluble in organic solvents and insoluble in
polar solvents such as water.
• They contain long hydrocarbon chains.
Example: fatty acids, glycerol, triglycerides, phospholipids, steroids and waxes.

Glycerol
• It is trihydroxy propane.
• Triglycerides: Many lipids have glycerol esterified with acids. These are called as
monoglycerides, triglycerides and triglycerides.
Phospholipids
• They have phosphorous and a phosphorylated organic compound. E.g. Lecithin

NUCLEIC ACID

• In the cell two types of nucleic acids are present - DNA (deoxyribonucleic acid) and RNA
(ribonucleic acid)
• DNA and RNA function as genetic material.
• These are polynucleotide which is made up of nucleotides.
• Nucleotides are joined together by a phosphodiester bond
• Nucleotide is composed of a nitrogen base, a pentose sugar (5-C) and a phosphate
• The nitrogen base is of two types-
Purine: adenine (A) and guanine (G)
Pyrimidine: cytosine (C), thymine (T) and uracil (U)
• Nucleotide: Nucleoside + phosphoric acid group
• Nucleoside: Nitrogenous bas + Pentose sugar
Watson - Crick Model

• DNA exists as a double helix.

• The two strands of polynucleotides are antiparallel
• Phosphodiester bond acts as back bone.
• Purine always form hydrogen bond with Pyrimidine (A pairs with T/U and G pairs with C)
• There are two hydrogen bonds between A and T and three hydrogen bonds between G and C.

ENZYMES
• All enzymes are proteins except ribozymes (nucleic acid).
• They act as catalysts. .
• They remain unchanged at the end of the reaction.
• Enzymes are highly substrate specific.
• Enzymes have active site where substrate binds.
• Enzymes get damaged at high temperatures i.e.
denaturation.
• Complete enzyme (holoenzyme) has protein part (Apo
enzyme) as well as non-protein part (cofactor)

Nature of Enzyme Action

• First, the substrate binds to the active site of the enzyme
• Formation of enzyme-substrate complex
• Formation of enzyme-product complex
• The enzyme releases the products of the reaction and the free enzyme is ready to bind to
another molecule of the substrate.

Concept of activation energy

• The minimum amount of energy required by
substrates to convert into the product is
called an activation of energy.
• Enzymes lower the activation energy of the
reaction they catalyse.

Co-factors (non-protein constituent) - prosthetic

groups, co-enzymes and metal ions.
• Prosthetic groups: organic compounds, tightly
bound to the apoenzyme. For example, in
peroxidase and catalase, which catalyze the
breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is a
part of the active site of the enzyme.
• Co-enzymes: organic compounds, loosely bound to the apoenzyme. e.g., coenzyme NAD and
NADP contain the vitamin niacin.
• Metal ions: e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase.
Classification and Nomenclature of Enzymes

Factors Affecting Enzyme Activity

Temperature and pH:
At specific temperature and pH enzyme shows optimum reaction. Low temperature preserves the
enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because
proteins are denatured by heat.
Concentration of Substrate
With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first. The
reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in the
concentration of the substrate.
Inhibitors
Some chemicals that may inhibit the rate of reactions are called inhibitors. When the inhibitor closely
resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as
a competitive inhibitor. e.g., inhibition of succinic dehydrogenase by malonate.
IMPORTANT QUESTIONS
Very Short Answer Type Questions
1- What is true about enzyme ribozyme-
a- Non-protein enzyme
b- Present in ribosome
c- Both are correct
d- Both are incorrect
Ans: c
2- Which monosaccharide is present in human blood-
a- Glycerol
b- Glucose
c- Inulin
d- Maltose
Ans: b
3- Which acid is commonly used to make slurry of tissue during analysis of biomolecules?
a- Hydrocholic acid
b- Sulphuric acid
c- Trichloroacetic acid
d- Acetic acid
Ans: c
4- Which bond is present between two nucleotides-
a- Peptide bond
b- Glycosidic bond
c- Phosphodiester bond
d- Hydrophobic bond
Ans: c
5- Assertion: Sucrose is a disaccharide.
Reason: It is made up of glucose and galactose.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.
Ans: c
6- Assertion: Cellulose is a homopolymer.
Reason: It is made up of only one type of monosaccharide unit, glucose.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.
Ans: a
7- Assertion: Co-enzymes are organic compounds loosely attached to apoenzymes
Reason: NADP is an example of a coenzyme.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.
Ans: b
8- How many carbon atoms are present in Palmitic acid and Arachidonic acid respectively-
a- 16 and 20
b- 20 and 16
c- 12 and 20
d- 16 and 12
Ans: a
9- Chitin is an example of –
a- Tertiary protein
b- Hetero polysaccharide
 c- Homo polysaccharide
d- Unsaturated fatty acid
Ans: b
10- Adenosine is composed of-
a- Adenine + Sugar
b- Adenine + Phosphate
c- Adenine + Adenine
d- Adenine + Thymine
Ans: a

Short Answer Type Questions

1- Give one example of each of the acidic and neutral amino acids.
Ans: acidic (glutamic acid), neutral (valine)
2- How unsaturated fatty acids differ from saturated fatty acids. Oils belong to which category.
Ans: Saturated- without double bond (Eg. Palmitic acid)
Unsaturated- with one or more C=C double bonds s (Eg. oleic acid)
Oils are unsaturated fatty acids
3- Give molecular structures of the followings-
Glycine, ribose sugar, Palmitic acid
Ans:

4- Mention the role of the following

GLUT-4, Collagen
Ans: GLUT-4- Enables glucose transport into cells
Collagen - Intercellular ground substance
5- Why does the shelf life of fruits increase in a refrigerator?
Ans: At low temperatures, the enzymatic activities of microorganisms slowdown, which helps to
prevent the growth of food-spoiling microorganisms and ultimately prevents food spoilage.
6- Write the monomers of the following-
Inulin, starch, glycogen, cellulose
Ans: inulin: fructose
starch, glycogen, cellulose: glucose
7- When stained with iodine solution the starch gives bluish colour while cellulose remains
unaffected. Give reason.
Ans: Starch forms helical secondary structures. In fact, starch can hold iodine molecules in the
helical portion. The starch-iodine is blue in colour. Cellulose does not contain complex helices
and hence cannot hold iodine.
8- What is the active site? Write its importance.
Ans: the active site is a cleft-like structure in enzymes.
It is the binding site for the substrate. At this site enzyme-substrate complex is formed.
9- What do you mean by Vmax in reference to enzymes?
 Ans: With the increase in substrate concentration, the velocity of the enzymatic reaction rises at
first. The reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any
further rise in the concentration of the substrate.
10- How do temperatures affect the rate of enzymatic reactions?
Ans: Low temperature preserves the enzyme in a temporarily inactive state whereas high
temperature destroys enzymatic activity because proteins are denatured by heat.
11- Write two differences in the DNA and RNA.
Ans: DNA: contain Deoxyribose sugar and thymine base
RNA: contain ribose sugar and Uracil base in place of thymine
12- Explain the structure of a quaternary protein.
Ans: haemoglobin consists of 4 subunits. Two subunits of α type and two subunits of β type
together constitute the human haemoglobin (Hb).
13- Peptide bond formation is related with dehydration. Provide a
diagram of a peptide bond.
Ans: peptide bond is formed when the carboxyl (-COOH) group of
one amino acid reacts with the amino (-NH2) group of the next
amino acid with the elimination of a water moiety (the process is
called dehydration).
14- How are glycosidic bonds formed?
Ans: The glycosidic or ketone group of a monosaccharide bind with an alcoholic group of
another organic compound to join the two compounds together.

Long Answer Type Questions

1- a- List the different types of lipids
b- Why are monosaccharide sugars known as reducing sugars?
Ans: a- Lipids are of three types: -
(i) Simple lipids: - they are alcohols or triglycerides containing fatty acid & glycerol.
(ii) Compound lipids: - They are simple lipids with a biologically active compound in them
eg. glycolipids (carbohydrate lipid) lipoprotein (protein + lipids)
(iii) Derived lipids: - They are hydrolyzed products of simple lipids such as fatty acids & alcohol.
b- Such sugars are called reducing sugars because they have a free aldehyde or ketone group &
can reduce Cu++ to Cu+
2- Give a detailed account of the classification of enzymes.
Ans:
3- Explain the different types of protein structures that occur in nature.
Ans: Primary structure: it is a linear arrangement of amino acids in a polypeptide chain.
Secondary structure: it is formed by the reorganization of linear polypeptide chains either in the
form of a sheet (alpha sheet structure) or in helical form (beta-helix). The chains are stabilized
by peptide and hydrogen bonds.
Tertiary protein: it provides a 3d structure and is stabilized by peptide bonds, hydrogen bonds,
ionic bonds, and disulphide bonds.
Quaternary protein: it consists of more than one polypeptide that forms a large multiunit
protein.
4- (i) Describe the mechanism of enzymatic action.
(ii) What is the activation of energy?
Ans: (i) First, the substrate binds to the active
site of the enzyme
Formation of enzyme-substrate complex
Formation of enzyme-product complex
The enzyme releases the products of the reaction and the free enzyme is ready to bind to
another molecule of the substrate
(ii) The minimum amount of energy required by substrates to convert into product is called an
activation of energy. Enzymes lower the activation energy of the reaction they catalyse.
5- (i) In what ratio are purine and pyrimidine present in DNA?
(ii) What is the antiparallel nature of DNA?
(iii) Who proposed the double helical model of DNA?
(iv) Define the bond which acts as the backbone of the polynucleotide strand.
Ans: Purine: Pyrimidine= 1:1
(ii) DNA is moistly double-stranded. The polarity of both strands is in opposite directions. The
polarity of one strand is 5’ to 3’ then the other strand will have 3’ to 5’ end polarity.
(iii) Watson and Crick
(iv) Phosphodiester bond acts as a backbone.
It is formed in between 3’OH of one nucleotide and 5’ Phosphate of another nucleotide
6- (i) Describe the structure of phospholipids. Give one example.
(ii) Explain the composition of triglycerides.
(iii) list any four roles of lipids.
Ans: (i) Phospholipids have only 2 fatty acids attached to the glycerol while the 3rd glycerol
binding site holds a phosphate group.
Example: Lecithin
(ii) Fat is ester of fatty acids with glycerol. When each molecule of glycerol reacts with three
molecules of fatty acid, triglyceride is formed.
(iii) Lipids are storage products in plants (cotyledons) as well as animals (adipose tissues).
Plasma membrane of cell is made up of two layers of lipids.
They also form phospholipids, glycolipids, and sterols.
They take part in the synthesis of steroid hormones, vitamin D, and bile salts.