Biology (university) · Part 01
Cell structure and membranes
The parts of prokaryotic and eukaryotic cells, and how the membrane controls what gets in and out.
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- Prokaryotic cellA small, simple cell with no nucleus. Its DNA floats in a region called the nucleoid. Bacteria and archaea are prokaryotes.
- Eukaryotic cellA cell whose DNA sits inside a nucleus and which has membrane-bound compartments called organelles. Animals, plants, fungi and protists are eukaryotes.
- NucleusThe organelle that stores DNA and controls which genes are used. It is wrapped in a double membrane with pores that let molecules pass.
- Endomembrane systemA linked set of membrane compartments that make, sort and ship proteins and lipids. It includes the rough ER, smooth ER, Golgi apparatus, lysosomes and vesicles.
- EndosymbiosisThe idea that mitochondria and chloroplasts began as free-living bacteria swallowed by an ancestral cell. Evidence: they have their own circular DNA, bacteria-sized ribosomes and double membranes.
- CytoskeletonA network of protein fibres that gives a cell its shape, moves organelles and drives cell movement. The three types are microfilaments (actin), intermediate filaments and microtubules.
- Fluid mosaic modelThe membrane is a double layer of phospholipids with proteins floating in it. The parts can move sideways, so the layer is fluid, and the mix of proteins makes it a mosaic.
- OsmosisThe movement of water across a selectively permeable membrane from lower solute concentration to higher solute concentration. Water moves toward the saltier side.
- Active transportMoving a substance across a membrane against its concentration gradient, using energy (usually ATP). Carrier proteins called pumps do the work.