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Biomolecules
Biomolecules may be defined as the lifeless organic substances which form the basis of
life and are responsible for the growth and maintenance of the living systems.
Biomolecules essential for the life process are carbohydrates, proteins, lipids and nucleic
acids.
Carbohydrates are naturally occurring organic compounds of carbon, hydrogen and
oxygen, distributed as Glucose, fructose, sucrose, starch, cellulose, etc. The ratio of
hydrogen and oxygen as 2 : 1 and they can be represented by the general formula
Cx(H2O)y where x and y are integers and may be the same or different.
Glucose
=
Sucrose
=
Rhamnose =
Deoxyribose =
C6H12O6
C12H22O11 or C12(H2O)11
do not have hydrogen and oxygen in the ratio of 2 :1 and
C6H12O5
C5H10O4
cannot be called as hydrates of carbon.
In fact oxygen is present in the form of (-CHO), Keto (>C=0) or hydroxyl (-OH gp).
Now carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or large
polymeric molecules which on hydrolysis yield polyhydroxy aldehydes and ketones.
Classifications:
(1) Monossaccharides: They are polyhydroxy aldehydes or ketones which cannot be
decomposed further by hydrolysis to give simpler carbohydrates.
G.F = (CH2O)n = 3 – 7
Glucose, fructose C6H12O6, galactose C6H12O6, ribose C6H10O5 etc
(2) Oligosaccharides: They on hydrolysis give a definite number (2 – 10) molecules of
monosaccaharides. They can be further divided into:
Disaccharides: Carbohydrates which upon hydrolysis gives 2 units of the same or
different monosaccharides.
Sucrose
Maltose
Lactose
-
C12H22O11
C12H22O11
C12H22O11
Trisaccharides: They upon hydrolysis furnish 3 units of the same or different
monosaccharides.
e.g. Raffinose
Glucose Fructose Galactose
𝐶18 𝐻22 𝑂16 + 2 𝐻2 𝑂
𝐻+
�⎯⎯⎯�
𝐶6 𝐻12 𝑂6 + 𝐶6 𝐻12 𝑂6 + 𝐶6 𝐻12 𝑂6
Tetrasaccharides: They upon hydrolysis give 4 units of the same or different
monosaccharides.
Glucose Fructose Galactose
𝐻+
C24H42O21 + 3H2O �⎯⎯⎯� 𝐶6 𝐻12 𝑂6 + 𝐶6 𝐻12 𝑂6 + 2𝐶6 𝐻12 𝑂6
Polysaccharides : They upon hydrolysis give a large number of monosaccharides.
They have large molecular masses. Their General Formula = (C6H10O5)n where n
= 100 – 3000
Example: Starch, Cellulose, glycogen, etc.
Classification on the basis of taste:
Sugars: Sweet to taste. Glucose, fructose
Non-Sugars: Not sweet. Starch
Reducing behaviours:
Reducing Sugars:
Carbohydrates which are capable of reducing Tollen’s and Fehling’s
e.g. Monosaccharides and disaccharides except sucrose.
Non Reducing sugars:
Carbohydrates which are unable to reduce Tollen’s reagent and Fehling’s solution.
E.g. Sucrose.
Monosaccharides : Classification.
Based on the nature of functional gp present. They are classified as
Aldoses : Possessing an (-CHO) gp are termed as Aldoses.
Ketones: possessing a C = O gp are called ketones.
Their structural formulae:
CHO
(CHOH)n
CH2OH
n = 1,2,3,4, or 5
CH2OH
C=O
(CHOH)n
CH2OH
Kotoses n = 1,2,3 or 4
Open Chain:
Hexoses – C6H12O6
Structure of D-Glucose
H–C=O
Ketohexose
CH2OH
H – C – OH
C=O
HO – C – H
HO – C – H
H – C – OH
H – C – OH
H – C – OH
H – C – OH
CH2OH
CH2OH
Cyclic form:
The five membered ring structure contains 4 – carbon atoms and an oxygen atom and is
called the furanose form.
Resemblance with (C4H4O)
Six membered ring structure contains five carbon atom and a pyranose form due to
resemblance with C5H6O.
Test for Glucose
Glucose
Decolourises Bromine water and
the solution becomes colourless
CHO
(CHOH)4
CH2OH
Fructose
Does not decolourise the red colour of
Br2 water
No reaction
𝐵𝑟.𝑊𝑎𝑡𝑒𝑟
+ (O)�⎯⎯⎯⎯⎯�
COOH
(CHOH)4
CH2OH
D – gluconic acid
Proteins
Proteins are highly complex, nitrogenous organic compounds having very high molecular
masses. They are polyamines form from alpha amino acids.
Amino acids are the building units of proteins. They possess both an amino group and a
carboxylic group.
They are classified Fibrous and globular proteins.
Based on the number of -NH2 and –COOH group, amino acids that are present in protein
can be classified into 3 categories.
(1) Neutral - eg. Glycine, Valine, Alanine – equal number of NH2 and COOH group.
(2) Acidic amino acid – 2 COOH groups and 1 NH2 group – eg. Asparatic acid,
Glutamic acid
(3) Basic amino acid – 2 NH2 and 1 COOH – eg Lysine, arginine, etc.
Primary Structures of proteins:
The primary structure of proteins refers to the sequence of amino acids held together by
peptide linkages.
Secondary structures of proteins:
In a protein Peptide chains are arranged in a definite shape. The determination of this
shape gives the secondary structure of proteins.
Secondary Structures:
The lone pair of electrons on the N-atom in the peptide bond is delocalized over the C=O
group. As a result C-N bond acquires a partial double bond character. The amide part
CO-NH is planar and rigid.
Iso-electric point:
An amino acid exists as a positive ion in acidic solution and as a negative ion in the basic
solution. Therefore, on passing current, it will migrate towards the cathode in acidic
solution and towards the anode in basic solution. Hence, at a particular pH of the
solution, the amino acid molecule should not migrate to either electrode and should exist
as a neutral dipolar ion. This pH is known as Isoelectric point.
Denaturation of proteins:
Proteins are very sensitive to the action of heat, acids, alkalis and electrolytes. When
they are subjected to heat, acid and alkali they undergo coagulation to form fibrous
proteins which are insoluble in water. This results in a change of physical and biological
properties of protein. The coagulated protein thus obtained is called denatured protein
and the process is called denaturation.
Formation of zwitter ion:
In aqueous solution the acidic carboxyl (-COOH) group loses a proton which is taken by
the basic amino group.
Zwitter ion is neutral but contains positive and negative charges. Due to the dipolar
nature, it is also referred to as a dipolar ion. The amino acids exist in this form. They
show amphoteric behaviour and react with both acids and bases.
Enzymes:
Enzymes are the important class of globular proteins which acts as a biocatalysts in the
living species and are produced in the living cells. Eg. Invertase, Amylase, Maltose,
Lactose.
Mechanism:
It follows a lock and key mechanism. It assumes the existence of active sites and cavities
on the surface of the enzymatic molecules.
I.
Binding the enzyme (E) on the substrate (S) to form an enzyme – substrate
complex.
E + S → ES
Enzyme – Substrate complex
II.
III.
Products formation in the complex
ES → EP
Enzyme-Substrate complex
Enzyme product
Release of the product from the enzymes
EP → Enzyme + Product
Vitamins: Group of organic compounds which are required in very small amounts for the
healthy growth and normal functioning of animal organisms. They are classified as:
(1) Fat Soluble vitamins: Not readily soluble in water – e.g. Vitamin A, D, E and K
(2) Water Soluble vitamins: e.g Vitamin B, B complex, Vitamin C
Deficiency and their diseases
Vitamin A
Vitamin B Complex
(a) Vitamin B1
(b) Vitamin B2
(c) Vitamin B3
(d) Vitamin B6
(e) Vitamin B12
Vitamin C
Vitamin D
Vitamin E
Vitamin K
Vitamin H
Coenzyme Q10
-
Night Blindness, Xerosis
-
Beri Beri
Cheilosis, cracking of lips, inflammation of tongue
Dermatitis ,graying of hairs and retardation of body and
Mental health.
Anaemia, Nervous disorders, Insomnia, Pellogra
Anaemia, Inflammation of tongue and mouth
-
Scurvy, bleeding of gums, skin diseases
Rickets, deformation of bones and teeth
Sterility, Muscular atrophy
Haemorrhage, Lengthening of the time of blood clotting
Dermatitis, loss of hair and paralysis
Low order of immunity of body against many diseases
Nucleic Acid
Nucleic Acids constitute an important class of biomolecules which are present in the
nuclei of all living cells. They are biopolymers. The monomer present in them are called
nucleotide. A nucleotide consists of three chemical constituents: a sugar, a nitrogen
containing heterocyclic base and phosphate group.
Composition and Primary Structure of Nucleic Acids:
Nucleic acids are the polymers of nucleotides. Their composition and primary structures
are described below:
Constituents of Nucleic Acids
A nucleotide consists of three chemical constituents: a sugar, a nitrogen containing
heterocyclic base, and a phosphate group.
(i)
Sugars in nucleic acids: Two types of pentose sugars have been obtained by the
hydrolysis of nucleic acids. They are 𝛽 - D – ribose and 𝛽- D – 2 deoxyribose. Their
structures are as follows:
(ii)
In these sugars, the C1 is an anomeric carbon. Therefore, both the sugars can
exist in 𝛼 and 𝛽 − forms.
The nucleotide present in DNA contains 𝛽 -D-2
deoxyribose, whereas that present in RNA contains 𝛽-D-ribose.
Nitrogen bases in nucleic acids: The nitrogen base is a residue present in a
nucleotide, is a heterocyclic nitrogenous base and is a derivative of either purine or
pyrimidine.
Thus, the nitrogen bases present in nucleic acids belong to either of the following
two classes of heterocyclic nitrogenous bases.
(a) Purines: The commonly found purines are adenine (abbreviated as A) and
guanine (G).
(b) Pyrimidines: The commonly found pyrimidines are thymine (T), cytosine (C) and
uracil (U).
The base residues present in RNA are adenine (A), guanine (G), cytosine (C) and
uracil (U); while those present in DNA are adenine (A), guanine (G), cystosine (C)
and thymine (T).
(iii)
Phosphate group: A nucleotide possesses a phosphoric acid unit. This unit is
responsible for linking nucleotides together in a nucleic acid molecule. The
phosphoric acid unit can be represented as given below:
DNA : Deoxyribonucleic acid