Enzymes Lecture Notes

Introduction to Enzymes

• Enzymes speed up biochemical reactions by lowering activation energy.
• Generally named after their reactions, making it easier to understand their function (e.g., DNA polymerase).
• Common suffix: "ase" in enzyme names.

Naming Examples

• DNA Polymerase: Catalyzes DNA replication by forming DNA polymers.
• Hexokinase: Catalyzes the first step of glycolysis; adds phosphate to glucose (a six-carbon sugar).

Categories of Enzymes

Enzymes are divided into six categories based on the types of reactions they catalyze:

1. Transferases

• Function: Transfer functional groups (X) from one molecule (B) to another (A).
• Example: Peptidyl transferase in protein translation transfers amino acids to a growing polypeptide chain.

2. Ligases

• Function: Catalyze joining of two molecules (A + B = AB).
• Example: DNA ligase joins DNA strands during replication.

3. Oxidoreductases

• Function: Involve electron transfer between molecules.
• Subtypes: Oxidases (removal of electrons) and reductases (addition of electrons).
• Example: Lactate dehydrogenase in lactic acid fermentation transfers electrons from NADH to pyruvate.

4. Isomerases

• Function: Convert molecules into their isomers.
• Example: Phosphoglucose isomerase converts glucose-6-phosphate to fructose-6-phosphate in glycolysis.

5. Hydrolases

• Function: Use water to cleave molecules into two parts.
• Example: Serine hydrolases break peptide bonds using a serine residue.

6. Lyases

• Function: Catalyze dissociation of a molecule without using water or oxidation.
• Example: Argininosuccinate lyase in the urea cycle breaks down argininosuccinate into arginine and succinate.
  • Lyases form double bonds or rings due to the mechanism of breaking bonds.

Summary

• Enzymes are named after the reactions they catalyze.
• Six types of enzymes: Transferases, Ligases, Oxidoreductases, Isomerases, Hydrolases, and Lyases.
• Each type has a unique function in biochemical reactions.