MAP The Section at a Glance
- 59 questions, 95 min. Content mix (approx.): Biochem ~25%, Biology ~65%, plus gen/organic chem in a biological context.
- Heavy on experiments, figures, and data interpretation — reason from the passage.
Central themes: structure→function, energy flow, information flow (DNA→RNA→protein), homeostasis and feedback.
Amino-acid focus: nine amino acids are essential (must come from diet): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine. For the exam, prioritize the charge/polarity classes below — they drive most questions, not the essential list.
BC Biochemistry — Amino Acids & Proteins
Amino Acid Classes (20)
| Class | Members |
|---|---|
| Nonpolar | Gly, Ala, Val, Leu, Ile, Pro, Met, Phe, Trp |
| Polar uncharged | Ser, Thr, Cys, Tyr, Asn, Gln |
| Acidic (−) | Asp, Glu |
| Basic (+) | Lys, Arg, His |
| Aromatic | Phe, Tyr, Trp (UV 280 nm) |
| Special | Gly (achiral, flexible), Pro (kink), Cys (disulfide) |
Charge & pI
- All (except Gly) are L, chiral. Zwitterion at physiologic pH.
- pI = pH of net-zero charge. Below pI → protonated (+); above pI → (−).
- Titratable groups: α-COOH (~2), α-NH₃⁺ (~9–10), plus side chains (Asp/Glu ~4, His ~6, Cys ~8, Lys ~10.5, Arg ~12.5).
Protein Structure
| Level | Defined by |
|---|---|
| Primary | aa sequence (peptide bonds) |
| Secondary | α-helix, β-sheet (backbone H-bonds) |
| Tertiary | 3-D fold (R-group interactions, disulfides) |
| Quaternary | multiple subunits |
Denaturation (heat, pH, urea) disrupts 2°–4° but not 1°. Chaperones aid folding.
Enzymes
- Lower activation energy; don't change ΔG or Keq.
- Models: lock-and-key, induced fit.
- Cofactors (metals), coenzymes (organic, e.g. NAD⁺, FAD from vitamins).
- Regulation: allosteric, feedback inhibition, covalent (phosphorylation), zymogens.
Enzyme Kinetics
Michaelis–Menten v = V_max[S]/(K_m+[S])
K_m = [S] at ½V_max (↓K_m = ↑affinity)
Lineweaver–Burk: 1/v vs 1/[S] (linear)
| Type | V_max | K_m |
|---|---|---|
| Competitive | — | ↑ |
| Noncompetitive | ↓ | — |
| Uncompetitive | ↓ | ↓ |
| Mixed | ↓ | ↑/↓ |
Cooperativity & Hemoglobin
- Allosteric/cooperative binders (hemoglobin) give a sigmoidal (S-shaped) curve, not hyperbolic — binding one ligand raises affinity for the next.
- Hemoglobin (cooperative, 4 subunits) vs myoglobin (hyperbolic, 1 subunit, higher affinity).
- Right shift = ↓ O₂ affinity, unloads to tissue: ↑CO₂, ↓pH (Bohr effect), ↑temperature, ↑2,3-BPG.
Biomolecules
- Carbs: mono/di/polysaccharides; glycosidic bonds; glycogen (branched storage), cellulose (β, structural).
- Lipids: triglycerides (storage), phospholipids (membranes, amphipathic), steroids (cholesterol → hormones), fat-soluble vitamins (ADEK).
- Nucleic acids: nucleotide = sugar + phosphate + base; A-T(U), G-C; antiparallel.
Fig 1. Michaelis–Menten kinetics. K_m is the substrate concentration giving half of V_max (lower K_m = higher affinity). Competitive inhibitors are overcome by more substrate (same V_max, higher apparent K_m); noncompetitive inhibitors lower V_max regardless of substrate (K_m unchanged).
MET Metabolism & Bioenergetics
Glucose Oxidation Map
| Stage | Location | Yield |
|---|---|---|
| Glycolysis | cytosol | 2 ATP, 2 NADH, 2 pyruvate |
| Pyruvate → acetyl-CoA | mito matrix | 2 NADH (×2 pyr) |
| TCA (×2 turns) | matrix | 6 NADH, 2 FADH₂, 2 GTP |
| ETC / Ox-phos | inner membrane | NADH≈2.5, FADH₂≈1.5 ATP |
| Total | ≈30–32 ATP |
Key Regulation
- Glycolysis rate-limiting: PFK-1 (activated by AMP/F-2,6-BP; inhibited by ATP/citrate).
- TCA rate-limiting: isocitrate dehydrogenase.
- Insulin → storage (glycogenesis, lipogenesis); glucagon/epi → breakdown (glycogenolysis, gluconeogenesis).
Other Pathways
- Anaerobic: pyruvate → lactate (regenerates NAD⁺); only 2 ATP.
- Gluconeogenesis: liver; reverses glycolysis at 3 irreversible steps.
- β-oxidation: fatty acids → acetyl-CoA (lots of ATP); occurs in mito.
- Ketogenesis: fasting/low-carb, from acetyl-CoA (liver).
- PPP: makes NADPH + ribose-5-P (biosynthesis, not ATP).
ETC & Chemiosmosis
- NADH enters at complex I, FADH₂ at complex II; e⁻ flow drives H⁺ pumping at complexes I, III, IV (complex II does not pump) → proton gradient.
- ATP synthase (complex V) uses H⁺ flow to make ATP. O₂ = final e⁻ acceptor → H₂O.
- Uncouplers (e.g., dinitrophenol) dissipate gradient → heat, no ATP.
Fig 2. Aerobic glucose oxidation. Glycolysis (cytosol) → pyruvate → acetyl-CoA → TCA cycle (mitochondrial matrix) feeds electron carriers into the electron transport chain, where oxidative phosphorylation yields the bulk of ATP. Without O₂, pyruvate is reduced to lactate to regenerate NAD⁺.
MB Molecular Biology & Genetics
Central Dogma
- Replication (S phase): semiconservative; helicase, primase, DNA pol (5′→3′), leading vs lagging (Okazaki), ligase, telomerase.
- Transcription (nucleus): RNA pol II; pre-mRNA → 5′ cap, poly-A tail, splicing (introns out, exons kept).
- Translation (ribosome): initiation (AUG=Met), elongation, termination (stop codons UAA/UAG/UGA); tRNA anticodons.
Mutations
| Type | Effect |
|---|---|
| Silent | same aa (degeneracy) |
| Missense | different aa |
| Nonsense | premature stop |
| Frameshift | insertion/deletion (not ×3) |
Gene Regulation
- Prokaryote: operons (lac = inducible; trp = repressible).
- Eukaryote: transcription factors, enhancers/silencers, epigenetics (DNA methylation ↓, histone acetylation ↑ expression).
Biotechnology
- PCR = amplify DNA (denature, anneal, extend). Gel = separate by size (− → +).
- Blots: Southern (DNA), Northern (RNA), Western (protein).
- Sanger sequencing; recombinant DNA (restriction enzymes, plasmids); CRISPR.
Mendelian Genetics
- Dominant/recessive; Punnett squares; incomplete dominance, codominance.
- X-linked recessive: affects males more; carrier mothers.
- Autosomal recessive: skips generations; consanguinity.
Hardy–Weinberg
p + q = 1
p² + 2pq + q² = 1
p²=homozygous dominant, 2pq=heterozygous, q²=homozygous recessive. Assumes no selection, mutation, migration, drift; random mating; large population.
Fig 3. The central dogma. DNA is replicated and transcribed to mRNA (nucleus); mRNA is translated to protein at the ribosome. The genetic code is degenerate (multiple codons per amino acid) and read in non-overlapping triplets from a start (AUG) to a stop codon.
CELL Cell Biology & Physiology
Organelles
- Nucleus (DNA), mitochondria (ATP, own DNA), rough ER (protein synth), smooth ER (lipids, detox), Golgi (modify/ship), lysosome (digest), peroxisome (β-oxidation, H₂O₂).
- Cytoskeleton: microfilaments (actin), intermediate, microtubules (mitosis, transport).
Membrane Transport
| Type | Energy |
|---|---|
| Simple/facilitated diffusion | none (down gradient) |
| Primary active (Na⁺/K⁺ ATPase) | ATP |
| Secondary active | ion gradient |
| Osmosis (water) | none |
Na⁺/K⁺ ATPase: 3 Na⁺ out, 2 K⁺ in per ATP.
Cell Cycle
- G₁ → S (DNA copy) → G₂ → M (mitosis: PMAT) → cytokinesis.
- Checkpoints (G₁/S, G₂/M) gate progression; p53 guards; cyclins/CDKs drive.
- Meiosis: 2 divisions → 4 haploid gametes; crossing over (prophase I) → diversity.
Signaling & Endocrine
- Peptide hormones → surface receptors → 2nd messengers (cAMP), fast.
- Steroid hormones → cross membrane → intracellular receptors → gene transcription, slow.
- Feedback: mostly negative (e.g., HPA axis).
Neuron & Action Potential
- Resting ~ −70 mV (Na⁺/K⁺ ATPase + K⁺ leak).
- Depolarize (Na⁺ in) → repolarize (K⁺ out) → hyperpolarize → refractory.
- All-or-none; saltatory conduction (myelin, nodes of Ranvier).
Systems Snapshot
- Circulatory: heart → arteries → capillaries → veins; left heart systemic, right pulmonary.
- Respiratory: gas exchange at alveoli; O₂/CO₂ diffusion.
- Renal: nephron — filter (glomerulus), reabsorb, secrete; regulates volume, pH, electrolytes.
- Digestive: mechanical + enzymatic; absorption in small intestine.
- Immune: innate (fast, nonspecific) + adaptive (B cells/antibodies, T cells).
Fig 4. Action potential. A stimulus reaching threshold (~−55 mV) opens voltage-gated Na⁺ channels (rapid depolarization); K⁺ channels then open to repolarize, briefly overshooting to hyperpolarization. The refractory period ensures one-way propagation.