CH-9 (BIOMOLECULES) BIOLOGY CLASS -XI, CBSE NCERT EXAM NOTES

Chapter-9
Biomolecules

Points to Remember

Biomolecules : All the carbon compounds that we get from living tissues.

Biomicromolecules : Molecules which have molecular wights less than one thousand dalton. They are also know as monomers. They are found in acid souble fraction.

Biomacromolecules : A biomolecule with molecular weight in the range of ten thousand daltons and above; found in acid insoluble fraction. e.g., polysaccharidea, nucleic acids, proteins and lipids.

How to analyse chemical composition of living tissues?

Primary and Secondary Metabolites :

• Primary metabolites have ifentifiable functions and play important roles in normal physiological process e.g., Amino acids, Nitrogenous bases, Proteins and nucleic acid.
• Secondary metabolites are product of certain metabolic pathways from primary metabolites, e.g., Carotenoids, drugs, alkaloids, essential oils, rubber, gum, cellulose and resins etc.

Amino acids : Organic compounds containing an amino group anf one carboxyl group (acid group) and both thses group are attached to the same carbon atom called a carbon and so they are called amino acids.
• Twenty Types of amino acids.
  Amino acid exists in Zwitterionic form at different pHs.
• Based on number of amino and carboxyl groups, amino acids can be :
(i) Aromatic - Tryptophan, phenylalanine and Tyrosine are aromatic (give smell) amino acids.
(ii) Acidic Amino Acids - (Aspartic acid, glutamic acid). Basic amino acid (Arginine) and Neutrak amibo Acids (Valine, Proline)

Lipids :

Lipids are not stictly macromolecules as their molecular weight do not excreed 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 gruop (contains 1 to 19 carbons).
• Fatty Acis : Saturated : With single bonds is carbon chain, e.g., Palmitic acid, bityric acid.
• Unsaturated : Withone or more double bonds, e.g., oleic acid, linoleic acid.
• Glycerol : A simple lipix, is trihydroxy propane.
• Some lipid have fatgy acids esterified with glycerol.
• Example of fatty acid (Palmitic acid) (CH₃ - (CH₂)₁₄ - COOH)
• They can be monoglycerides,diglycerides and triglycerides.
Triglyceride (R ₁, R ₂, R ₃ are alkyl group in fatty acids.)
Phospholipids (Lecithin) found in cell membrane and lipids made complex structure in neural tissue.

Phospholipids are compounds lipids with phosphorus and a phosphorylated organic compound e.g., Lecithin.

Nucleoside : Nitrogenous base + Sugar e.g., Adenosine, guanosine.

Nucleotide : Nitrogenous base + Sugar + Phosphate group. e.g., Adenylic acid, Guanylic acid. Thymidlicacid.

Nucleic acids : Deoxyribonucleic (DNA) and ribonucleic acid (RNA) DNA structure (Watson and Crick Model) :

1. DNA is a right handed, double helix of two polynucleotide chains, having a major and minor groove.

2. The two chains are antiparallel, and held together by hydrogen bonds (two between A and T and three between C and G)

3. The backbone is formed by sugar-phosphate-sugar chain.

4. The nitrogen bases are projected more or less perpendicular go this, backbone and face inside.

5. The pitch is 34A. At each step of ascent the strand turns 36. The rise per base pair is 3.4A, so one full turn involves ten base pairz.

Protein : Protein are polypeptides.

• They are polymers of aminoacids linked by peptide bond.
• Iz a heteropolymer (different monomers repeating 'n' number of times).
• Functuons : Intercellular ground substanve (collagen), as enzyme (Tdypsin) as hormone (Insuline), go fight infections (Antibodies), as sensery releptors, and ti enable glucose transport in cells (GLUT-4)

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 avid and last amino acid is called C-terminal amino acid.

(b) Secondary Structure : polypeptide chain undergoes folding or coiling which is stablized-by hydrigen bonding. Right handed helics are observed; e.g. fibrous protein in hair, nails.

(c) Tertiary structure : Long prote8ns chain is floded upon itself a hollow woollen ball. Gives a 3-fimensional view of protein, e.g, myosin.

(d) Quaternary structure : Two or more polypeptides with their folding and coiling are arranged with respect to each other, e.g., Human haemoglobin molecule has 4 peptide chains - 2 a and 2 b Subunits.

Monosaccharides : are joined by glycosidic bond, right end is reducing and left and is onon 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 fiber is cellulose.

(c) Glycogen : It a branched Homopolymer, found as storage polysaccharidea in animals.

(d) Inulin : Is a polymer of fructose.

(e) Chitin : Chemically modified sugar (amino-sugars) N-acetyl galactosamine form exoskeleton of arthropods; homopolymer.

Metabolic Pathways :

(a) Anabolic Pathways : Lead to formation of more complex structure form a simpler structure with the consumption of energy e.g., Protein form amino acids, also know as biosynthetic pathways.

(b) Catabolic Pathways : Lead to formation of simpler structure from a complex structure e.g., Gluscose → 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 metaolism, there cannot be a living state.

Bonds linking monomers in a polymer

Peptide bond Formed between the carboxyl (-COOH) group of one amino acid, and the amino (-NH ₂) group of the next amino with the elimination of water moiety, (dehydration).

Glycolipids 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 succeding nucleotide. ( The bond between phosphate group and hydroxyl group of sugar).

Ezymes : Are biocatalyst.

• Almost all emzymes 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 fits.
• Enzymes get damaged at high temperatures.
• Enzymes isolated from thermophilic organism (living under high termperatures) are thermostable.
• Enzymes accelerate the reactions many folds.
• Enzymes lower the activation energy of reactions.
• E + S == ES → EP → E + P
where E == Ezymes, S == Substrate, P == Prodct

Factors affecting enzyme activity :

(a) Temperature : Show highest activity at optimum temperature. Activity decline above and below the optimum value.

(b) pH : Enzymes function in a narrow range of pH. Highest activity at optimum pH.

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

Enzyme inhibition : When the binding of a chemical shuts off enzyme acitivty, the process is called inhibition and chemical is called inhibitor.

Competitive inhibition : Inhibition closely the substrate in its molecular structure and inhibits the enzymes activity. e.g., inhibition of succinic dehydrogenase by malonate. (Actual substrate 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 gruop 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 gruop 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.
• Coenzyme : These are organic compounds whose association with the apoenzyme is only transient, usually occuring during the course of catalasis.
e.g., Coenzyme Nicotinamide adenine dinucleotide (NAD) and NADP contain vitamin niacin.
• Metal ions : Meta 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.