Cell Biology and Basic Biochemistry
This domain tests how cell structure relates to function, how biological molecules are built and detected, and how membranes and enzymes control reactions. Expect organelle identification, microscopy calculations, biomolecule tests and enzyme-kinetics graphs.
Cells and organelles
Prokaryotes have no nucleus or membrane-bound organelles, 70S ribosomes and a peptidoglycan wall; eukaryotes have 80S ribosomes and compartmentalisation. Mitochondria carry out aerobic respiration, chloroplasts photosynthesis, rough ER protein synthesis and transport, smooth ER lipid synthesis, the Golgi modification and packaging, and lysosomes hydrolysis. Magnification = image size ÷ actual size; resolution is the ability to distinguish two close points and is improved by shorter wavelengths, as in electron microscopy.
Biomolecules and tests
Carbohydrates, proteins and nucleic acids are condensation polymers; hydrolysis reverses the linkage. Benedict's test detects reducing sugars with a brick-red precipitate on heating; iodine turns blue-black with starch; Biuret gives purple with protein; the emulsion test gives a white emulsion with lipid.
Membranes and enzymes
The fluid mosaic model describes phospholipids, proteins, cholesterol and glycoproteins. Movement occurs by diffusion, facilitated diffusion, osmosis, active transport and co-transport. Enzymes lower activation energy; Vmax is reached at saturation and Km is the substrate concentration at half Vmax. Competitive inhibitors raise Km but leave Vmax unchanged; non-competitive inhibitors lower Vmax.
Worked example
An enzyme has Vmax 20 µmol min⁻¹ and Km 4 mmol dm⁻³. With inhibitor A, Vmax remains 20 but Km rises to 12. This is competitive inhibition: the inhibitor occupies the active site, so more substrate is needed for half-maximal rate, but excess substrate displaces it and restores Vmax.
Traps
Write that mitochondria release ATP, not 'produce energy'. Benedict's needs heating. Do not confuse magnification with resolution, and do not assume every inhibitor lowers Vmax.