Structure and Function of Proteins and Enzymes
What you must know
Proteins fold into shapes determined by sequence and environment; function follows structure. Enzymes lower activation energy without changing reaction equilibrium or ΔG. Know Michaelis–Menten kinetics: Vmax is the maximum rate at saturating substrate; Km is the substrate concentration at half Vmax and inversely reflects enzyme–substrate affinity. Understand inhibition: competitive inhibitors raise apparent Km but leave Vmax unchanged (overcome by more substrate); noncompetitive inhibitors lower Vmax without changing Km; uncompetitive inhibitors lower both. Know allosteric regulation (cooperativity, sigmoidal kinetics) and covalent modification (phosphorylation). Recognize that enzymes are sensitive to pH and temperature and that cofactors/coenzymes are required for activity.
Traps
Do not say an enzyme changes ΔG or equilibrium-it only speeds the approach to equilibrium. Watch for questions that ask which inhibitor is overcome by increasing substrate (competitive). Also be careful distinguishing Km (affinity proxy) from Vmax (capacity).
Worked rule of thumb
Use the inhibitor signature table: competitive → ↑Km, Vmax same; noncompetitive → Km same, ↓Vmax; uncompetitive → both ↓. Identify the signature before solving.
Quick example
At [S] = Km, velocity is half of Vmax. If a competitive inhibitor is added, the new apparent Km rises, so at the same [S] velocity falls-but adding more substrate can restore Vmax.