Chapter - 9

Biomolecules
Biomolecules

Points to Remember
Biomolecules : All the carbon compounds that we get from living tissues.
Biomicromolecules : Molecules which have molecular weights less than
one thousand dalton. They are also known as monomers.
Biomacromolecules : Have molecular weight more than 10000 daltons
(generally 10,000 deltons and above). They are generally polymers.
Biomacromolecules : A biomolecule a with molecular weight in the
range of ten thousand daltons and above; found in acid insoluble fraction. e.g.
polysaccharides, nucleic acids, proteins and lipids.

Primary and secondary metabolites :

 Primary metabolites have identiiable functions and play important roles in
normal physiological process eg. Amino acids, nitrogenous bases, proteins
and nucleic acid.
 Secondary metabolites are product of certain metabolic pathways from
primary metabolites, eg. carotenoids, drugs, alkaloids, essential oils, rubber,
gum, cellulose and resins etc.
Amino acids : Organic compounds containing an amino group and one
carboxyl group (acid group) and both these groups are attached to the same
carbon atom called α carbon and so they are called amino acids.

e.g. (1) In Glycine R = H

(2) In alanine R = CH3
(3) In serine R = CH2 – OH

Click here for more PDFs - https://www.jeeneetforall.in/

  Twenty types of amino acids.
Amino acid exists in Zwitterionic form at different pHs.
R R R
| | |

(A) (B) (C)

(Zwitterionic form)
 Based on number of amino and carboxyl groups, amino acids can be :
(i) Aromatic–Tryptophan, phenylalanine and Tyrosine are aromatic (give
smell) amino acids.
Amino Acids

Polar

Acidic Basic Neutral

e.g. aspartic acid e.g., Arginine e.g. valine, Proline
glutamic acid
(ii) Non Polar—Glutamine, tyrosine, serine

Lipids :
Lipids are not strictly macromolecules as their molecular weight do not
exceed 800 Da but form a part of the acid insoluble pool.
 Water insoluble, containing C, H, O.

 Fats on hydrolysis yield fatty acids.

 Fatty acid has a carboxyl group attached to an R group (contains 1 to 19

carbons).
 Fatty Acids : Saturated : With single bonds in carbon chain, e.g., Palmitic

acid, butyric acid.

Unsaturated : With one or more double bonds, e.g., oleic acid, linoleic acid.
 Glycerol : A simple lipid, is trihydroxy propane.

 Some lipid have fatty acids esteriied with glycerol.

Example of fatty acid (Palmitic acid) (CH3—(CH2)14—COOH)
92

Click here for more PDFs - https://www.jeeneetforall.in/

  They can be monoglycerides, diglycerides and triglycerides.

3
Triglyceride (R1, R2, R3 are alkyl groups in fatty acids.)
Phospholipids (Lecithin) found in cell membrane and lipids made complex
structure in neural tissue.
 Phospholipids are compound lipids with phosphorus and a phosphorylated
organic compound e.g., Lecithin.
Nitrogen bases
(Carbon compounds with heterocyclic rings)

Purine : Adenine, Guanine, Pyrimidine : Cytosine, Uracil, Thymine.

Nucleoside : Nitrogenous base + Sugar e.g. Adenosine, guanosine.
Nucleotide : Nitrogenous base + Sugar + Phosphate group. e.g. Adenylic
acid, Guanylic acid. Thymidylic acid.
Nucleic acids : Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA structure (Watson and Crick Model) : DNA is a right handed, double
helix of two polynucleotide chains, having a major and minor groove. The two
chains are antiparallel, and held together by hydrogen bonds (two between A
and T and three between C and G). The backbone is formed by sugar-phosphate-
sugar chain. The nitrogen bases are projected more or less perpendicular to this,
backbone and face inside. The pitch is 34A°. At each step of ascent, the strand
turns 36°. The rise per base pair is 3.4°A, so one full turn involves ten base pairs.
Protein : proteins are polypeptides.
 They are polymers of aminoacids linked by peptide bond.
 Is a heteropolymer (different monomers repeating ‘n’ number of times).
 For functions of proteins refer Table 9.5, Page no. 147 NCERT, Text Book
of Biology for Class XI.

93

Click here for more PDFs - https://www.jeeneetforall.in/

Structure of Proteins
(a) Primary structure : Is found in the form of linear sequence of amino acids.
First amino acid is called N-terminal amino acid and last amino acid is called
C-terminal amino acid.
(b) Secondary structure : Polypeptide chain undergoes folding or coiling which
is stabilized-by hydrogen bonding. Right handed helices are observed; e.g.,
ibrous protein in hair, nails.
(c) Tertiary structure : Long protein chain is folded upon itself like a hollow
woollen ball. Gives a 3-dimensional view of protein, e.g., myosin.
(d) Quaternary structure : Two or more polypeptides with their foldings and
coilings are arranged with respect to each other, e.g., Human haemoglobin
molecule has 4 peptide chains - 2 α and 2 β Subunits.
Monosaccharides are joined by glycosidic bond, right end is reducing and
left end is non reducing
Polysaccharides : Are long chain of polymers of monosaccharides.
(a) Starch : Store house of energy in plant tissues. Forms helical secondary
structures, made of only glucose monomers.
(b) Cellulose : Homopolymer of glucose. It does not certain complex helices.
Cotton ibre is cellulose.
(c) Glycogen : Is a branched homopolymer, found as storage polysaccharide in
animals.
(d) Inulin : Is a polymer of fructose.
(e) Chitin : Chemically modiied sugar (amino-sugars) N-acetyl galactosamine
form exoskeleton of arthropods; heterpolymer.
Metabolic Pathways :
(a) Anabolic pathways : Lead to formation of more complex structure from a
simpler structure with the consumption of energy, e.g., Protein from amino
acids., also known as biosynthetic pathways.
(b) Catabolic pathway : Lead to formation of simpler structure from a complex
structure, e.g., Glucose → Lactic Acid + energy
The most important energy currency in living systems is ATP (adenosine
tri – phosphate).
“There is no uncatalysed metabolic conversion in living system”
The living state is a non-equilibrium steady state to be able to perform work.
Without metabolism, there cannot be a living state.

94

Click here for more PDFs - https://www.jeeneetforall.in/

Bonds linking monomers in a polymer
Peptide bond—formed between the carboxyl (–COOH) group of one amino
acid, and the amino (– NH2) group of the next amino with the elimination of water
moiety, (dehydration).
Glycosidic bond—bond formed between two carbon atoms of two adjacent
monosaccharides., by dehydration.
Phosphodiester bond—bond formed in nucleic acids where in a phosphate
moiety links the 3-carbon of one sugar of one nucleotide to the 5-carbon of the
sugar of the succeeding nucleotide. (The bond between phosphate group and
hydroxyl group of sugar)
Ezymes : Are biocatalyst.
 Almost all enzymes are proteins.

 Ribozymes–Nucleic acid that behave like enzymes.

 Has primary, secondary and tertiary structure.

 Active site of an enzyme is a crevice or pocket into which substrate its.

 Enzymes get damaged at high temperatures.

 Enzymes isolated from thermophilic organisms (live under high temperatures)

are thermostable.
 Enzymes accelerate the reactions many folds.

 Enzymes lower the activation energy of reactions. (Fig. 9.6, Page no. 156,

NCERT Text Book of Biology for Class XI).

 E + S == ES → EP → E + P

where E = Ezymes, S = Substrate, P = Product

Factors affecting enzyme activity :

(a) Temperature : Show highest activity at optimum temperature. Activity
declines above and below the optimum value.
(b) pH : Enzymes function in a narrow range of pH. Highest activity at optimum
pH. (Fig. 9.7, Page no. 157, NCERT, Text Book of Biology for Class XI).

95

Click here for more PDFs - https://www.jeeneetforall.in/

 (c) Concentration of substrate : The velocity of enzymatic reaction rises with
increases in substrate concentration till it reaches maximum velocity (Vmax).
Further increase of substrate does not increase the rate of reaction as no free
enzyme molecules are available to bind with additional substrate.

KM value : The substrate concentration at which Vmax x is half of a reaction.

Enzyme inhibition : When the binding of a chemical shuts off enzyme

activity, the process is called inhibition and chemical is called inhibitor.

Competitive inhibition : Inhibitor closely resembles the substrate in its

molecular structure and inhibits the enzyme activity. E.g., inhibition of succinic
dehydrogenase by malonate. (Actual is succinic acid).

Classification of enzymes :
1. Oxidoreductase/dehydrogenases : Catalyse oxidoreduction between 2
substrates. S reduced + S′ oxidised → S′ oxidised + S′ reduced.
2. Transferases : Catalyse transfer of a group between a pair of substrates.
S – G + S′ → S + S′ – G
3. Hydrolases : Catalyse hydrolysis of ester, ether, peptide, glycosidic, C–C,
P-N bonds.
4. Lyases : Catalyse removal of groups from substrates by mechanisms other
than hydrolysis. Leave double bonds.
5. Isomerases : Catalyse inter-conversion of optical, geometrical or positional
isomers.
6. Ligases : Catalyse linking together of 2 compounds.
C–O, C–S, C–N, P–O
Co-factors : Enzymes becomes catalytically become active when it binds
to non protein constituent called co-factors. Protein portion of enzyme is
called apoenzyme.
 Prosthetic group : These are organic compound which tightly bound to the
apoenzyme.
e. g., Haem is prosthetic group in peroxidase and catalase.

Click here for more PDFs - https://www.jeeneetforall.in/

  Coenzyme : These are organic compounds whose association with the
apoenzyme is only transient, usually occurring during the course of catalysis.

e.g., Coenzyme Nicotinamide adenine dinucleotide (NAD) and NADP

contain vitamin niacin.

 Metal ions : Metal ions form coordination bond with side chains at the
active site and at the same time form one or more coordination bond with
substrate.

e.g. zinc in enzyme carboxy peptidase.

Click here for more PDFs - https://www.jeeneetforall.in/

Powered by TCPDF (www.tcpdf.org)