Structure of enzymes, Classification of enzymes. Examples, significance.

1. Definition:
   • Enzymes are biological catalysts that speed up biochemical reactions without being consumed in the process.
2. Molecular Structure:
   • Proteins:
     • Most enzymes are globular proteins.
     • Made up of one or more polypeptide chains folded into a specific three-dimensional shape.
   • Active Site:
     • The region where substrate molecules bind and undergo a chemical reaction.
     • Specific shape fits only certain substrates ("lock and key" or "induced fit" model).
   • Cofactors:
     • Non-protein molecules required for enzyme activity.
     • Types:
       • Metal ions: e.g., Zn²⁺, Mg²⁺.
       • Coenzymes: Organic molecules like vitamins (e.g., NAD⁺, FAD).
   • Allosteric Sites:
     • Secondary binding sites for regulatory molecules that influence enzyme activity.
3. Levels of Protein Structure:
   • Primary Structure: Sequence of amino acids.
   • Secondary Structure: Alpha helices and beta sheets.
   • Tertiary Structure: 3D folding due to interactions like hydrogen bonding and disulfide bridges.
   • Quaternary Structure: Complex of multiple polypeptide chains (e.g., hemoglobin).

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Classification of Enzymes

Enzymes are classified into 6 major classes based on the type of reaction they catalyze (International Union of Biochemistry and Molecular Biology)

Class	Type of Reaction Catalyzed	Examples
1. Oxidoreductases	Oxidation-reduction reactions (transfer of electrons).	Dehydrogenases (e.g., Lactate dehydrogenase).
2. Transferases	Transfer of functional groups (e.g., methyl, phosphate).	Kinases (e.g., Hexokinase).
3. Hydrolases	Hydrolysis (breaking bonds using water).	Proteases (e.g., Trypsin), Lipases.
4. Lyases	Addition/removal of groups to form double bonds.	Decarboxylases (e.g., Pyruvate decarboxylase).
5. Isomerases	Rearrangement of atoms within a molecule.	Isomerases (e.g., Phosphoglucose isomerase).
6. Ligases (Synthetases)	Bond formation coupled with ATP hydrolysis.	DNA Ligase, Acetyl-CoA synthetase.

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Examples of Enzymes and Their Functions

Enzyme	Substrate	Function
Amylase	Starch	Breaks down starch into maltose (in saliva).
Pepsin	Proteins	Breaks proteins into smaller peptides (stomach).
DNA Polymerase	DNA nucleotides	Synthesizes new DNA strands.
Lipase	Fats	Hydrolyzes triglycerides into glycerol and fatty acids.
Carbonic Anhydrase	Carbon dioxide	Converts CO₂ and H₂O to bicarbonate and H⁺ ions.

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Significance of Enzymes

1. Biological Importance:
   • Catalysis of Metabolic Reactions:
     • Essential for cellular functions like digestion, respiration, and biosynthesis.
   • Specificity:
     • Highly specific for their substrates, ensuring precise control of reactions.
   • Regulation:
     • Allosteric regulation and feedback inhibition control metabolic pathways.
2. Industrial Applications:
   • Food Industry:
     • Amylases for brewing, lipases for cheese production.
   • Medical Field:
     • Enzyme replacement therapy (e.g., in lactose intolerance).
     • Diagnostic tools (e.g., liver enzymes for liver function tests).
   • Pharmaceuticals:
     • Production of antibiotics and drugs using enzymatic synthesis.
   • Biotechnology:
     • DNA polymerases in PCR for genetic research.
3. Environmental Applications:
   • Biodegradation of pollutants (e.g., enzymatic treatment of oil spills).
   • Detergents containing enzymes like proteases and lipases for stain removal.

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Key Features of Enzymes

• Catalytic Efficiency: Enzymes accelerate reactions up to 10⁶–10¹² times faster than uncatalyzed reactions.
• Specificity: Recognize only specific substrates.
• Reusability: Not consumed in the reaction; can be used repeatedly.
• Optimal Conditions: Function best at specific temperatures and pH ranges.