Biochemistry Foundations for the MCAT

Amino Acids & Protein Structure

20 standard amino acids classified by side chain:

• Nonpolar: G, A, V, L, I, P, F, W, M
• Polar: S, T, C, Y, N, Q
• Positively charged: K, R, H
• Negatively charged: D, E

Protein Structure:

• Primary: amino acid sequence
• Secondary: α-helix, β-sheet (H-bonds)
• Tertiary: 3D fold (hydrophobic, ionic, disulfide)
• Quaternary: multiple subunits

Enzyme Kinetics

$v = \frac{V_{max}[S]}{K_m + [S]} \quad \text{(Michaelis-Menten)}$

• Competitive inhibitor: Increases apparent Km, Vmax unchanged
• Non-competitive inhibitor: Decreases Vmax, Km unchanged

Metabolism

• Glycolysis: Glucose → 2 pyruvate + 2 ATP + 2 NADH (cytoplasm)
• Krebs Cycle: Acetyl-CoA → 2 CO₂ + 3 NADH + 1 FADH₂ + 1 GTP
• ETC/Oxidative Phosphorylation: NADH → ~2.5 ATP; FADH₂ → ~1.5 ATP
• Total from glucose: ~30-32 ATP