Define enzymes. Classify them according to the IUB system and explain their mechanism of action.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. Enzymes are biological catalysts, mostly proteins, that speed up reactions in cells without being changed themselves. They are highly specific for their substrates.
2 · Classify (IUB, six classes).
1 Oxidoreductases: lactate dehydrogenase.
2 Transferases: hexokinase, ALT.
3 Hydrolases: amylase, pepsin.
4 Lyases: aldolase.
5 Isomerases: triose phosphate isomerase.
6 Ligases: pyruvate carboxylase.
3 · Draw the mechanism. [Diagram: E + S → ES complex → E + P; and an energy graph showing lower activation energy with the enzyme]
4 · Explain the active site and the two models.
Active site: cleft where the substrate binds.
Lock-and-key (Fischer): rigid fit.
Induced fit (Koshland): flexible site.
5 · Define the related terms. Holoenzyme = apoenzyme + cofactor (metal ion or coenzyme). Mention prosthetic group and zymogen.
6 · Significance. Enzymes control every pathway. Blood enzyme levels (ALT, AST, CK) help diagnose liver and heart disease.
7 · Nutrition link. B vitamins form coenzymes; zinc, magnesium and iron act as metal cofactors.
8 · Close in one line. Enzymes make the reactions of life fast, specific and controllable.
Scoring tip: One example per class is enough. A neat activation-energy graph earns easy marks.
Write-up practice
The check looks for key words only. It does not grade your answer and never writes it for you.