Discuss the role of B-complex vitamins as coenzymes.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. Coenzymes are non-protein organic molecules that help enzymes by carrying hydrogen, electrons or chemical groups. Most are made from B-complex vitamins.
2 · Draw a holoenzyme. [Diagram: apoenzyme + coenzyme → holoenzyme, with the substrate at the active site]
3 · Tabulate the B vitamins.
B1 → TPP: oxidative decarboxylation.
B2 → FMN, FAD: hydrogen transfer.
B3 → NAD+, NADP+: hydrogen transfer.
B5 → CoA: acyl transfer.
B6 → PLP: transamination.
Biotin: carboxylation.
Folate → THF: one-carbon transfer.
B12 → methylcobalamin, deoxyadenosylcobalamin.
4 · Group them by function.
Hydrogen carriers: NAD+, NADP+, FMN, FAD.
Group carriers: TPP, CoA, PLP, biotin, THF, B12 coenzymes.
5 · Significance. Every major pathway (glycolysis, TCA cycle, ETC, fat and amino acid metabolism) depends on these coenzymes.
6 · Nutrition link. Deficiency stops the enzyme: beriberi (B1), pellagra (B3), megaloblastic anaemia (folate, B12). B12 comes only from animal foods.
7 · Close in one line. B vitamins are needed in small amounts because they are recycled as coenzymes, yet without them metabolism stalls.
Scoring tip: A four-column table (vitamin, coenzyme, reaction, enzyme) is the fastest way to score full marks.
Write-up practice
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