Overview
This lecture introduces enzymes, explaining their role as biological catalysts that lower activation energy in biochemical reactions, especially in breaking down starch molecules.
Breakdown of Starch and Hydrolysis
- Starch is composed of amylose and amylopectin, made from alpha-glucose units linked by alpha-1,4 glycosidic bonds.
- Breaking glycosidic bonds requires a hydrolysis reaction, which means splitting the bond with water.
- Water alone, without extra energy, cannot break glycosidic bonds in starch.
- High energy (activation energy) is needed for water to break these bonds effectively.
- The body cannot reach such high temperatures to provide this energy safely.
Role of Enzymes as Catalysts
- Enzymes are biological catalysts that weaken bonds, making it easier for reactions like hydrolysis to occur.
- Enzymes do not break bonds directly; they lower the activation energy needed for the reaction.
- With enzymes, less energy is needed for water to break the glycosidic bond.
Structure and Properties of Enzymes
- Enzymes are globular proteins with complex 3D shapes (tertiary or quaternary structure).
- Globular proteins are spherical and water-soluble.
- Enzymes are usually named ending with "ase" (e.g., helicase, polymerase), though not always.
Importance of Enzymes in Cells
- Different types of enzymes are required for various chemical reactions in cells:
- Peptidyl transferase for protein synthesis.
- ATP synthase for ATP production.
- Acyl-CoA dehydrogenase for lipid breakdown.
- Helicase and DNA polymerase for DNA synthesis.
- Without enzymes, essential cell reactions such as protein synthesis, lipid breakdown, ATP synthesis, and DNA replication could not occur.
Key Terms & Definitions
- Enzyme — a protein that acts as a catalyst, reducing activation energy for biochemical reactions.
- Glycosidic bond — a covalent bond joining carbohydrate (sugar) molecules.
- Hydrolysis — a chemical reaction that uses water to break a bond.
- Activation energy — the minimum energy required to start a chemical reaction.
- Catalyst — a substance that speeds up a reaction without being consumed.
Action Items / Next Steps
- Review Chapter 2 on globular proteins and starch structure.
- Preview upcoming chapters for details on specific enzymes (e.g., helicase and DNA polymerase in Chapter 6, ATP synthase in Chapter 12).