Overview
This lecture explains how B vitamins function as coenzymes, enabling enzymes to catalyze biochemical reactions critical for energy production in the body.
Role of B Vitamins as Coenzymes
- B vitamins are essential parts of coenzymes required for enzyme activity.
- Coenzymes enable biochemical reactions by helping enzymes arrange substrates correctly.
- Enzymes are proteins that speed up reactions by lowering activation energy.
Enzyme Activation and Function
- Some enzymes are inactive until a specific coenzyme binds and alters their shape.
- Thiamine pyrophosphate (from Vitamin B1) must bind to its enzyme to process pyruvate and produce ATP.
- When the enzyme, coenzyme, and substrate (pyruvate) bind, the reaction occurs, yielding ATP and CO2.
- After reaction, products are released and the enzyme is ready to catalyze another cycle.
Alternate Coenzyme Mechanism: Allosteric Control
- Coenzymes can change an enzyme’s structure without interacting with the substrate directly.
- This conformational change (allosteric control) allows the enzyme to accept the substrate and catalyze the reaction.
B Vitamin Intake and Sources
- The body needs only small amounts of B vitamins for coenzyme function (e.g., 1.2 mg thiamine/day).
- Excess B vitamins are excreted in urine and do not increase energy production.
Table of B Vitamins, Sources, and Functions
- Thiamine (B1): Meat, leafy vegetables, grains, legumes – coenzyme for decarboxylation reactions.
- Riboflavin (B2): Milk, meat, grains – hydrogen carrier in oxidation-reduction reactions.
- Niacin (Nicotinamide): Meat, peanuts – hydrogen carrier in Krebs cycle, oxidative phosphorylation.
- Pyridoxine (B6): Meat, fish, poultry – aids protein metabolism reactions.
- Pantothenic Acid: Meat, grains, legumes, egg yolk – part of Coenzyme A.
- Biotin: Egg yolk, legumes, nuts, liver – involved in carboxylation, decarboxylation, deamination reactions.
Key Terms & Definitions
- Coenzyme — a small molecule (often derived from vitamins) that assists enzyme function.
- Enzyme — a protein that speeds up chemical reactions in the body.
- Allosteric control — regulation of an enzyme by binding a molecule at a site other than the active site, changing its shape.
- ATP (Adenosine Triphosphate) — the primary energy carrier in cells.
- Substrate — the molecule upon which an enzyme acts.
Action Items / Next Steps
- Review the table of B vitamins, their dietary sources, and coenzyme roles.
- Understand the process of enzyme activation by coenzymes and the concept of allosteric control.