Cell Biology and Molecular Biology
Core concepts
Candidates must be able to describe membrane structure and transport (passive diffusion, facilitated diffusion, active transport, osmosis), organelle function, the cell cycle and its checkpoints, and the central dogma: DNA replication, transcription, and translation. Know the differences between prokaryotic and eukaryotic cells, the role of ribosomes, the endoplasmic reticulum and Golgi in protein sorting, and mitochondria in oxidative phosphorylation. Understand enzyme kinetics (substrate affinity, saturation, competitive versus noncompetitive inhibition) and the factors that denature proteins.
Traps
Questions often confuse osmosis with diffusion, or assume water moves toward higher solute concentration rather than toward higher water potential (lower solute concentration). Another common trap is treating ATP yield of aerobic respiration as a fixed number, when textbooks differ; answer from the logic of the pathway rather than memorized totals. Watch for items that ask where a process occurs: transcription in the nucleus, translation on ribosomes, glycolysis in the cytoplasm, the Krebs cycle in the mitochondrial matrix.
Worked example
A cell is placed in a hypertonic solution. Rule of thumb: solute concentration outside is higher, so water leaves the cell and it shrinks (crenation in animal cells, plasmolysis in plant cells). If the question instead describes swelling or bursting, the solution was hypotonic.
Study tip
Draw the central dogma and label each step with its location and enzyme. Most molecular biology items can be answered by locating the step on that diagram.