Cell and Molecular Biology: Compartmentalization, Information Flow, and Membrane Dynamics
Core concepts
A candidate must be fluent in the central dogma and its exceptions (reverse transcription, RNA editing, prion-like templating), the endomembrane system and its directional traffic (ER → Golgi → plasma membrane or lysosome; retrograde COPI vs anterograde COPII), cytoskeletal motors (myosin on actin, kinesin toward microtubule plus ends, dynein toward minus ends), and the cell-cycle checkpoints with their cyclin-CDK pairings. Know membrane transport classes: simple diffusion, facilitated diffusion, primary active transport (Na+/K+-ATPase, 3 Na+ out, 2 K+ in), and secondary cotransport. Signal transduction frameworks-GPCR → adenylyl cyclase → cAMP → PKA; receptor tyrosine kinase → Ras → MAPK-should be traceable step by step.
Traps
Questions love directionality: which motor walks which way, which face of the Golgi receives vesicles, which way protons flow through ATP synthase. Another trap is conflating channel with pump (channels never require ATP and never move against a gradient) and conflating competitive with noncompetitive inhibition (Km rises vs Vmax falls). Watch for wording about "net" ATP yield versus gross, and about whether a process is transcriptional or post-transcriptional.
Worked rule of thumb
For any transport question, apply the two-question test: (1) Is the solute moving down or against its electrochemical gradient? (2) Is energy consumed directly (ATP hydrolysis) or borrowed from an existing gradient? Down-gradient plus no ATP means passive; up-gradient plus direct ATP means primary active; up-gradient powered by another ion's gradient means secondary active. This single test resolves most transport items quickly and consistently.
Study strategy
Rehearse pathway order aloud, then sketch each organelle's luminal versus cytosolic face, because many exam items hinge on topology rather than names.