Enzyme Reactions: Enzymes are sensitive to environmental condition. It could be affected by temperature, pH, substrate concentration and enzyme concentration. The rate of enzyme reaction is measured by the amount of substrate changed or amount of product formed, during a period of time.
Temperature: Heating increases molecular motion. Thus the molecules of the substrate and enzyme move more quickly resulting in a greater probability of occurrence of the reaction. The temperature that promotes maximum activity is referred to as optimum temperature.

pH: The optimum pH is that at which the maximum rate of reaction occurs. Thus the pH change leads to an alteration of enzyme shape, including the active site; If extremes of pH are encountered by an enzyme, then it will be denatured.

Substrate Concentration: For a given enzyme concentration, the rate of an enzyme reaction increases with increasing substrate concentration.
Enzyme Concentration: The rate of reaction is directly proportional to the enzyme concentration.

(i) Many enzymes require non-protein components called cofactors for their efficient activity. Cofactors may vary from simple inorganic ions to complex organic molecules. They are of three types: inorganic ions, prosthetic groups and coenzymes.
(ii) Holoenzyme: Active enzyme with its non-protein component.
(iii) Apoenzyme: The inactive enzyme without its non-protein component.
(iv) Inorganic ions help to increase the rate of reaction catalysed by enzymes. Example: Salivary amylase activity is increased in the presence of chloride ions.
(v) Prosthetic groups are organic molecules that assist in catalytic function of an enzyme. Flavin adenine dinucleotide (FAD) contains riboflavin (Vit B2), the function of which is to accept hydrogen. 'Haem' is an iron-containing prosthetic group with an iron atom at its centre.
(vi) Coenzymes are organic compounds which act as cofactors but do not remain attached to the enzyme. The essential chemical components of many coenzymes are vitamins. ego NAD, NADP, Coenzyme A, ATP.

Certain substances present in the cells may react with the enzyme and lower the rate of reaction. These substances are called inhibitors. It is of two types competitive and non-competitive inhibitors.

Competitive Inhibitor:
1. Molecules that resemble the shape of the substrate and may compete to occupy the active site of enzyme are known as competitive inhibitors.
2. Eg: The enzyme that catalyses the reaction between carbon dioxide and the CO2 acceptor molecule in photosynthesis, known as ribulose bisphosphate carboxylase oxygenase (RUBISCO) is competitively inhibited by oxygen/carbon-di-oxide in the chloroplast. The competitive inhibitor is malonate for succinic dehydrogenase.
Non-competitive Inhibitors:
1. There are certain inhibitors which may be unlike the substrate molecule but still combines with the enzyme.
2. This either blocks the attachment of the substrate to active site or change the shape so that it is unable to accept the substrate. Eg: The effect of the amino acids alanine on the enzyme pyruvate kinase in the final step of glycolysis.
(i) Certain non-reversible / irreversible inhibitors bind tightly and permanently to an enzyme and destroy its catalytic properties entirely. These could also be termed as poisons. Eg: Cyanide ions which blocks cytochrome oxidase in terminal oxidation in cell aerobic respiration.

1. Based on the R group amino acids are classified as acidic, basic, polar, non-polar.
2. The amino group of one amino acid reacts with carboxyl group of other amino acid, forming a peptide bond.
3. Two amino acids can react together with the loss of water to form a dipeptide. Long strings of amino acids linked by peptide bonds are called polypeptides. In 1953 Fred Sanger first sequenced the Insulin protein.
Structure of Protein:

1. Protein is synthesised on the ribosome as a linear sequence of amino acids which are held together by peptide bonds.
2. After synthesis, the protein attains conformational change into a specific 3D form for proper functioning.
3. According to the mode of folding, four levels of protein organisation have been recognised namely primary, secondary, tertiary and quaternary
(i) The primary structure is linear arrangement of amino acids ill a polypeptide chain.
(ii) Secondary structure arises when various functional groups are exposed on outer surface of the molecular interaction by forming hydrogen bonds. This causes the amino acid chain to twist into coiled configuration called a-helix or to fold into a flat \(\beta \) -pleated sheets.
(iii) Tertiary protein structure arises when the secondary level proteins fold into globular structure called domains.
(iv) Quaternary protein structure may be assumed by some complex proteins in which more than one polypeptide forms a large multi-unit protein. The individual polypeptide chains of the protein are called subunits and the active protein itself is called a multimer. Eg: Enzymes serve as catalyst for chemical reactions in cell and are non-specific. Antibodies are complex glycoproteins with specific regions of attachment for various organisms.