Cell Biology and Molecular Biology
What you must understand
Know the eukaryotic cell organelles and their functions: nucleus (DNA, transcription), mitochondria (aerobic respiration, ATP), chloroplasts (photosynthesis, plants only), ribosomes (protein synthesis), rough and smooth ER (protein processing, lipid synthesis), Golgi apparatus (modification and packaging), lysosomes (intracellular digestion), vacuoles (storage, turgor in plants), cytoskeleton. Distinguish plant vs animal cells (cell wall, chloroplasts, large central vacuole vs centrioles, lysosomes). Learn the cell cycle (interphase G1, S, G2; mitosis; cytokinesis) and the phases of mitosis (prophase, metaphase, anaphase, telophase). At molecular level know DNA structure (double helix, complementary base pairing A–T, G–C), replication (semi-conservative), transcription and translation (mRNA, tRNA, ribosomes, codon–anticodon). Understand diffusion, osmosis, active transport and membrane structure (phospholipid bilayer, proteins).
Traps candidates fall into
- Saying mitochondria "make energy" - they release energy by converting it into ATP; energy is not created.
- Confusing transcription (DNA → mRNA, in the nucleus) with translation (mRNA → protein, at the ribosome).
- Forgetting that in base pairing A pairs with T (DNA) but with U in RNA.
- Placing the S phase outside interphase, or mixing up metaphase (chromosomes align) with anaphase (chromatids separate).
- Confusing osmosis (water across a semi-permeable membrane) with diffusion of solutes.
Worked example / rule of thumb
If a DNA template strand reads 3′-TAC GGA-5′, the mRNA is 5′-AUG CCU-3′ (T→A, A→U, C→G, G→C). Rule of thumb for transport: with the concentration gradient and no energy = passive (diffusion/osmosis); against the gradient and energy (ATP) required = active transport.