Biology Chapter 9 Biomolecules
Chemicals or molecules present in the living organism are known as
biomolecules. Biomolecules are divided into two types- inorganic and
organic.
Inorganic biomolecules includes minerals, gases and water and organic
biomolecules includes carbohydrates, fats, proteins, nucleic acids, vitamins,
etc.
Different biomolecules can be classified as aldehyde, ketones and aromatic
compounds as chemical forms. The amino acids, nucleotides and fatty
acids can be classified as biochemical forms.
Except lipids, macromolecules are formed by polymerization of sub-units
called monomers.
Proteins are polymers of amino acids. Amino acids are linked by peptide
bond formed by dehydration between COOH group of one amino acids
and NH3 group of next with the removal of H2O.
Biomolecules class 11 Notes Biology
In nucleic acids, the phosphate molecules links 3’ C of sugar of one
nucleoside to the 5’ C of sugar of next nucleosides releasing two water
molecules to form 3’-5’ phosphodiester bond.
In polysaccharides, the mono-saccharides are linked by glycosidic
bonds formed by dehydration between two carbon atoms of two adjacent
monosaccharides.
Carbohydrates (Polysaccharides)
Polysaccharides are long chain of sugar containing different
monosaccharaides as a building block.
Starch is present in plants as store house of energy. It forms helical
secondary structure. It can hold the I2 molecules in the helical structure.
Cellulose molecules contain glucose molecules joined together by 1-4 β
linkage. It is the most abundant organic molecules on earth.
Glycogen is called animal starch as it is the reserve food materials for
animals, bacteria and fungi. In this, glucose molecules are arranged in
highly branched bush like chain having two types of linkage 1-4 α in
straight chain and 1-6 linkage in branching.
Proteins are polypeptide chains made up of amino acids. There are 20 types of amino
acids joined together by peptide bond between amino and carboxylic group. There are
two kinds of amino acids-
1. Essential amino acids are obtained by living organism along with food.
2. Non-essential amino acids can be prepared by our body from raw
materials.
Primary structure of protein is the basic structure of protein in which a
number of polypeptides are involved having sequence of amino acids. The
first amino acid of sequence is called N-terminal amino acid and last
amino acid of peptide chain is called C-terminal amino acid.
Secondary structure protein threads forms helix. There are three types of
secondary structure- α helix, β pleated and collagen. In α helix, the
polypeptide chain is coiled spirally in right handed manner.
In β pleated secondary proteins two or more polypeptide chains are
interconnected by hydrogen bonds. In collagen there are three strands or
polypeptides coiled around one another by hydrogen bonds.
In Tertiary structure long protein chain is folded upon itself like a hollow
woollen ball to give three dimensional view of protein.
(a) secondary structure (b) Tertiary structure
In Quaternary structure each polypeptide develops its own tertiary
structure and function as subunit of protein. Eg. Hemoglobin. In adult
human hemoglobin 4 sub-units are involved. The two subunits are of α
type and two subunits of β types.
Nucleic Acid: Nucleic acids are polynucleotides. A nucleic acid has three chemically
distinct components- heterocyclic compound ( nitrogenous base), polysaccharides
( ribose/ deoxy-ribose sugar) and phosphate or phosphoric acid.
The sugar found in nucleic acid is either ribose or deoxyribose. Nucleic
acid containing deoxyribose sugar is called DNA (Deoxyribonucleic Acid)
and those containing ribose sugars are called RNA (Ribonucleic acid).
Biomolecules are constantly being changed into some other biomolecules
and also made from other biomolecules. This breaking and making is
through chemical process called metabolism.
In living organism, all the metabolic reactions are enzyme catalyzed.
Catalysts are those substances that alter the rate of reaction. The protein
with catalytic power is called enzyme.
Enzymes
Enzymes are commonly proteinaceous substances which are capable of
catalysing chemical reactions of biological origin without themselves
undergoing any change. They are commonly called as biocatalysts.
The nucleic acids that behave like enzymes are called ribozymes.
The tertiary structure of protein/Enzyme has pockets or crevice into which
substrate fit to form ES complex.
The formation of the ES complex is essential for catalysis.
E+S ES →EP →E + P
The structure of substrate gets transformed into the structure of product
through formation of transient state structure.
The major difference between inorganic and organic catalyst is inorganic
catalyst works effectively at high temperature and pressure but enzyme
get damaged at high temperature.
The external energy required to start a chemical reaction is called
activation energy.
Factors influencing Enzyme Activity
1. Temperature- An enzyme is active within a narrow range of temperature.
Temperature ate which enzyme is most active is called optimum
temperature. The enzyme activity decrease above and below this
temperature.
2. pH – every enzymes has an optimum pH at which it is maximum active. Most of the
intracellular enzymes work at neutral pH.
3. Concentration of Substrate– increase in substrate concentration increases the rate
of
reaction due to occupation of more active sites by substrate.
Competitive Inhibitor- when the molecular structure of inhibitor
resembles the substrate, it inhibits the function of enzymes.
Enzymes are classified as
1. Oxidoreductases/Dehydrogenases–
S reduced + S’ oxidised S oxidised + S’ reduced
2. Transferases
S – G + S’ S + S’ – G
3. Hydrolases catalyses the hydrolysis of peptide, ester, glycosidic bonds et
4. Lyases remove the groups from substrate.
5. Isomerases-inter conversion of optical, geometrical or positional isomers.
6. Ligases – catalyses the linking together of two compounds.
Co-factors are the non-protein constituent of an enzyme which make the enzyme more
catalytically active. The protein portions of enzyme are called apoenzyme.
Prosthetic groups are organic compounds and are tightly bound to the apoenzyme. For
example, in peroxidase and catalase, which catalyze the breakdown of hydrogen
peroxide, haem is the prosthetic group
The essential chemical components of any coenzymes are vitamins. Example, coenzyme
NAD and NADP contain the vitamin niacin
