BIOMOLECULES
Introduction:
The Physical structure, the Emotional reactions, Growth factors,
Resistance capacities, Health.
All such kind of things in living beings are governed by a particular kind
of molecules, called Biomolecules.
The molecules that are involved to build-up the living bodies are
Biomolecules.
Ex: Carbohydrates, Proteins, Vitamins, Hormones, Lipids, Nucleic acids.
In your syllabus Vitamins, hormones are eliminated.
In this chapter, we study about
1) Carbohydrates - Glucose, Fructose, Sucrose.
2) Amino acids, Proteins
3) Nucleic acids - DNA, RNA
4) Lipids
Carbohydrates
Hydrates if carbon are called carbohydrates
Their formula is of the form Cn(H2O)m. But there are exception like
deoxyribose.
Chemically, carbohydrates are polyhydroxy aldehydes or polyhydroxy
ketones.
Classification of carbohydrates:
Based on the number of hydrolysis products, carbohydrates are
classified into 4 types.
1) Monosaccharides:
Carbohydrates which do not cleave during hydrolysis are called
monosaccharides.
Ex: Glucose, Fructose
2) Disaccharides:
Carbohydrates which give two monosaccharides on hydrolysis are
called disaccharides.
Ex: Maltose, Sucrose, Lactose
3) Oligo saccharides:
Carbohydrates which give a few monosaccharides in hydrolysis are
called oligosaccharides.
Ex: Raffinose (which gives glucose, fructose and galactose on
hydrolysis)
4) Polysaccharides:
Carbohydrates which give a large number of monosaccharides on
hydrolysis are called polysaccharides.
Ex: Starch (a polymer of glucose), Cellulose (a polymer of glucose)
Main functional group of carbohydrates:
1) Aldose:
If the main functional group is -CHO, then the carbohydrate is called
aldose.
Ex: Glucose
2) Ketose:
If the main functional group is C = 0, then the carbohydrate is called a
ketose.
Ex: Fructose
Preparation of Glucose:
1) From Sucrose(cane sugar):
If sucrose is boiled with dilute HCl or H2SO4 in alcoholic solution,
glucose and fructose are obtained in equal
amounts.
2) From Starch:
Commercially glucose is obtained by the hydrolysis of starch by boiling
it with dilute H2SO4 at 393 K under pressure.
Reducing sugars:
Those carbohydrates which contain free aldehyde or Ketonic group and
reduce Fehling’s solution or Tollen’s reagent are called reducing sugars.
Ex: All mono saccharides, Maltose and Lactose.
Non-reducing sugars:
Those carbohydrates which do not have free aldehyde or ketonic group
and do not reduce Fehling’s solution or Tollen’s reagent are called non-
reducing sugars.
Ex: Sucrose.
Amino acids, Proteins
Amino acids:
Amino acids are biomolecules which contain amino group (-NH2) and a
carboxylic acid group (-COOH) at <alpah>-carbon
Ex: Glycine, Alanine.
Essential amino acids:
Amino acids which cannot be synthesized in the body and must be taken
in diet are called essential amino acids.
Ex: Valine, leucine, phenylalanine etc.
Non essential amino acids:
Amino acids which can be synthesized in the body are known as non-
essential amino acids.
Ex: glycine alanine, glutamic acid etc.
Peptide linkage:
It is an amide linkage formed between -COOH group and -NH2 group.
When carbonyl group of one amino acid reacts with the amino group of
the other,a water molecule is eliminated and peptide linkage is formed.
Zwitter ion:
In amino acid, the -NH2 group is basic and -COOH group is acidic in
aqueous solution. The carboxylic group loses a proton and amino group
accepts the proton giving rise to a dipolar ion as zwitter ion.
Ex: Glycine ( H2N+-CH2-COO-)
Proteins:
Polymeric products of <alpha>-amino acids with molecular mass upto
10,000 are called polypeptides while those having molecular mass
greater than 10,000 are usually called proteins.
Ex: Keratin in hair.
Classification of Proteins with respect to their structure
Structure of Proteins:
There are four levels at which the structure of proteins are studied.
These are primary, secondary, tertiary and quaternary levels.
1) Primary structure of proteins:
The sequence in which various amino acids are arranged in protein is
called its primary structure. Any change in the sequence of amino acids
creates different protein which alters biological functions.
2) Secondary structure of proteins:
It refers to shape inwhich a long polypeptide chain exists. A protein
may assume <alpha>-helix structure of <beta>-pleated structure. The
<alpha>-helix structure results due to regular cooling of polypeptide
chain which is stabilized by intramolecular hydrogen bonding. Keratin in
hair, nails, wood and myosin in nucleus have <alpha>-helix structure. In
<beta>-pleated sheet structure, all peptide chains are stretched to
nearly maximum extension and then arranged side by side and held
together by intramolecular hydrogen bonding. Silk has b-pleated
structure.
3) Tertiary structure of proteins:
The tertiary structure of proteins represent overall folding of the
polypeptide chain i.e, further folding of the secondary structure. It gives
rise to two major molecular shapes namely fibrous and globular. The
main forces which stabilise 20 and 30 proteins are hydrogen bonds,
disulphide linkages, Van der waals forces and electrostatic force of
attraction.
4) Quaternary structure of proteins:
Some of the proteins are composed of two or more polypeptide chains
referred to as subunits.The spatial arrangement of these subunits with
respect to each other is known as quaternary structure.
Denaturation of proteins:
When a protein in its native form, is subjected to physical change as
change in temperature, or chemical change like changes in pH, the
hydrogen bonds are disturbed.
The protein globules unfold, helix get uncoiled and protein loses its
biological activity. This is called denaturation of protein.
Secondary and tertiary structures are destroyed but the primary
structure remains as such.
Ex: Coagulation of egg by boiling, curdling of milk etc.
Nucleic acids - DNA, RNA
The biomolecules which are found in the nuclei of living organisms in the
form of nucleo proteins or chromosomes are called nucleic acids. Nucleic
acids are of two types.
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
Functions of nucleic acids:
1) DNA, due to replication property, transmits hereditary characteristics
from one generation to another.
2) RNA and DNA help in the protein synthesis in the cell. RNA synthesis
the protein and DNA has the message of this synthesis.
Difference between RNA and DNA:
DNA RNA
The pentose sugar present in DNA The pentose sugar present in RNA
is D-2-deoxyribose is D-Ribose
DNA contains cytosin and thymine RNA contains cytosine and uracil as
as pyrimidine bases. pyramidine bases.
It has a double stranded <alpha>- It has a single stranded <alpha>-
helix structure. helix structure.
Its molecule is relatively long with Its molecule is relatively short with
high molecular mass. low molecular mass.
LIPIDS
Lipids are esters of long chain fatty acids and alcohols. They are naturally
occuring oily and greasy organic compounds. They are insoluble in water
but soluble in organic solvents like ether, benzene.
The common lipids are fats, oils, waxes, phospholipids, glycolipids,
steroids and terpenes. Ghee, butter, curd, fish oils etc are animal sources
of dietary lipids.
Groundnut oil , gingely oil, mustard oils etc. are vegetable sources of
dietary lipids.
