Cell structure
Eukaryotic and prokaryotic cell structure
Eukaryotic cells have a nucleus (double envelope with pores, chromatin, nucleolus that makes ribosomes) and membrane-bound organelles: rough ER (ribosomes; makes and transports proteins), smooth ER (lipids, steroids), Golgi body (modifies, packages proteins into vesicles), mitochondria (aerobic respiration, ATP; folded cristae), lysosomes (digestive enzymes), 80S ribosomes, centrioles and microtubules. Plant cells also have a cellulose cell wall, chloroplasts and a large vacuole. Prokaryotic cells are smaller, with no nucleus (circular DNA, plasmids), 70S ribosomes, a peptidoglycan (murein) wall and sometimes a capsule and flagellum. Viruses are non-living: nucleic acid in a protein capsid, sometimes an envelope.
≈ 45 minMicroscopy and magnification
Magnification ; convert to the same unit first (1 mm = 1000 µm; 1 µm = 1000 nm). Resolution is the ability to distinguish two close points: light microscopes resolve about 200 nm; electron microscopes about 0.5 nm because electrons have a much shorter wavelength. TEM gives 2D sections with internal detail; SEM gives 3D surface images; both need a vacuum, so specimens are dead. An eyepiece graticule is calibrated against a stage micrometer (divisions of known size, often 10 µm) at each objective. Cell fractionation: homogenise in cold, isotonic, buffered solution, then ultracentrifuge: nuclei sediment first, then mitochondria, then ribosomes.
≈ 40 min