POLYSACCHARIDES :
- Acid soluble pillet also has polysaccharides as another class of macromolecules.
- Polysaccharides are the long chain of sugars.
- Cellulose is homopolymer containing only glucose units.
- Starch is a variant of homopolymer of glucose which store energy.
- Glycogen is another homopolymer found in animal.
- Inulin is a polymer of fructose.
- In a polysaccharide chain the right end is called reducing end and left end is non-reducing end.
- Starch form helical secondary structure.
- Starch can hold Iodine (I2) molecule in its helical portion hence gives blue colour.
- Cellulose dose not contain complex helices and hence cannot hold Iodine (I2) and not give blue colour.
- Complex sugars have amino-sugar as building blocks. (Glucosamine, N-acetyl galactosamine.)
- Exoskeleton of arthropods made of complex sugar called chitin.
- Complex polysaccharides are heteropolymer.
STRUCTURE OF PROTEINS :
- 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.
- Secondary structure: Polypeptide chain undergoes folding or coiling which is stabilized by hydrogen bonding. Right handed helices are observed. e.g., fibrous protein in hair nails.
- Tertiary structure: Long protein chain is folded upon itself like a hollow woolen ball. Gives a 3-dimensional view of protein, e.g., myosin.
- 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 - 2α and 2β subunits.
NATURE OF BOND LINKING MONOMERS IN A POLYMER :
- Peptide bondb : Formed between the carboxyl (-COOH) group of one amino acid and the amino (-NH2) group of the next amino acid with the elimination of water moiety.
- Glycosidic bondb :
- Individual monosaccharides linked with each other to form polysaccharides.
- This bond is also formed by dehydration.
- Formed between two carbon atoms of two adjacent monosaccharides.
- Phosphodiester bondbb :
- In a nucleic acid a phosphate moiety links the 3’-carbon of one sugar one nucleotide to the 5’-carbon of the sugar of the succeeding nucleotide.
- The bond between the phosphate and hydroxyl group of sugar is an ester bond.
- There is one such ester bond on either side, it is called Phosphodiester bond.
- Anabolic pathways: Lead to formation of more complex molecules from a simpler molecules with the consumption of energy. e.g., Protein from amino acids.
- Catabolic pathway: Lead to formation of simpler molecule from a complex molecule. e.g., Glucose → Lactic Acid.
ENZYMES :
- Are biocatalysts.
- Almost all enzymes are proteins.
- Ribozyme - Nucleic acids 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 organisms (live under high temperatures) are thermostable.
- Enzymes accelerate the reactions many folds.
- Enzymes lower the activation energy of reactions.
- The chemicals on which the enzyme acts called substrates.
- Enzyme converts substrates into products.
Nature of enzyme action :
- The substrate binds to the active site of the enzyme, fitting into the active site.
- The binding of the substrate induces the enzymes to alter its shape, fitting more tightly around the substrate.
- Active site now breaks the chemical bond of the substrate and enzyme-product complex is formed.
- The enzyme releases the product.
Factors affecting enzyme activity :
- Temperature :
- Show highest activity at optimum temperature.
- Activity declines above and below the optimum value.
- pH :
- Enzymes function in a narrow range of pH.
- Highest activity at optimum pH.
- Concentration of substrate :
- The velocity of enzymatic reaction rises with increase in substrate concentration till it reaches maximum velocity (V max). Further increase of substrate does not increase the rate of reaction as no free enzyme molecules are available to find with additional substrate.
- 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.
Classification of enzymes :
- Oxidoreductase/dehydrogenases: Catalyse oxidoreduction between 2 substrates.
- Transferases: Catalyse transfer of a group between a pair of substrates.
- Hydrolases: Catalyse hydrolysis of ester, ether, peptide, glycosidic, C-C, P-N bonds.
- Lyases: Catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving a double bond in the product.
- Isomerases: Catalyse inter-conversion of optical, geometric or positional isomers.
- Ligases: Catalyse linking together of 2 compounds.
Cofactors :
- Non-protein constituents found to the enzyme to make it catalytically active.
- Protein portion of enzyme is called apoenzyme.
- Prosthetic groups: Are organic compounds tightly bound to apoenzyme. E.g., haem in peroxydase and catalase.
- Co-enzymes: Organic compounds which loosely bind with enzyme. E.g., NAD, NADP.
- Metal ions: Required for enzyme activity. Form coordination bond with side chains at active site and with substrate. E.g., zinc is a co-factor for enzyme enters stomach?
