Biochemistry: Amino Acids & Proteins
Free MCAT study guide — Biological and Biochemical Foundations of Living Systems
Amino Acid Structure
| Category | Amino Acids | Properties |
|---|---|---|
| Nonpolar | G, A, V, L, I, P, F, W, M | Hydrophobic, found in protein interior |
| Polar uncharged | S, T, C, Y, N, Q | H-bond donors/acceptors |
| Positive (pH 7.4) | K (10.5), R (12.5), H (6.0) | Charged at physiological pH (H partially) |
| Negative (pH 7.4) | D (3.65), E (4.25) | Deprotonated at physiological pH |
Key Point: Special amino acids: G (smallest, flexible), P (rigid ring, helix breaker), C (disulfide bonds), H (catalytic sites).
pI = (pKa₁ + pKa₂) / 2 (for AAs with no ionizable side chain)
Protein Structure
| Level | Bonds/Forces | Key Features |
|---|---|---|
| Primary (1°) | Peptide bonds (covalent) | Linear sequence — determines all higher structure |
| Secondary (2°) | H-bonds (backbone N-H↔C=O) | α-helices, β-sheets |
| Tertiary (3°) | R-group interactions | Hydrophobic, ionic, disulfide, H-bonds |
| Quaternary (4°) | Same as 3° | Multiple subunits (e.g., Hb α₂β₂) |
Enzyme Kinetics
v = Vmax[S] / (Km + [S])
| Inhibitor Type | Km Effect | Vmax Effect | Binds |
|---|---|---|---|
| Competitive | ↑ (apparent) | Unchanged | Active site |
| Noncompetitive | Unchanged | ↓ | Allosteric site |
| Uncompetitive | ↓ | ↓ | ES complex only |
| Mixed | ↑ or ↓ | ↓ | E or ES |
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