Biochemistry & Metabolism — Common Exam Question Types

1.Common question: given experimental data on Km and Vmax changes, identify the type of enzyme inhibition.

2.Strategy. If Km increases and Vmax stays unchanged, it is competitive inhibition — the inhibitor competes with substrate for the active site, but high substrate can overcome it.

3.If Km stays unchanged and Vmax decreases, it is noncompetitive inhibition — the inhibitor binds elsewhere, reducing effective enzyme count, cannot be overcome by adding substrate.

4.If both Km and Vmax decrease, it is uncompetitive inhibition — the inhibitor only binds the enzyme-substrate complex.

5.If you see a sigmoidal velocity curve in a multi-subunit enzyme, it is allosteric regulation, often with cooperative binding.

6.Common question: how many ATP are produced from complete oxidation of one glucose molecule? How many if a certain step is blocked?

7.Strategy. Memorize direct products of each stage: ATP, NADH, FADH2. Conversion: each NADH yields about two point five ATP via the electron transport chain. Each FADH2 yields about one point five ATP. Note the shuttle system loss for cytoplasmic NADH from glycolysis.

8.Common question: given a metabolic toxin, identify which step it blocks and the consequence.

9.Cyanide blocks Complex IV — stops electron transport chain, no ATP, lethal. Rotenone blocks Complex I — blocks NADH electron entry, major ATP reduction. Antimycin A blocks Complex III — between coenzyme Q and cytochrome c.

10.Oligomycin blocks ATP synthase — H plus return is stopped, no ATP synthesis. DNP, dinitrophenol, is an uncoupler — H plus freely crosses membrane, proton gradient dissipates, energy lost as heat.

11.Fluoride blocks enolase in glycolysis step nine. Arsenic replaces phosphate in glycolysis step seven, causing arsenolysis with no ATP yield.

12.Common question: what metabolic pathways do insulin or glucagon promote or inhibit?

13.One principle: Insulin equals STORE — lowers blood glucose by promoting glycolysis, glycogen synthesis, and lipogenesis.

14.Glucagon equals RELEASE — raises blood glucose by promoting glycogen breakdown (glycogenolysis), gluconeogenesis, and lipolysis.