6.1 Organelles, Compartmentalization and Trafficking

Membrane-bound organelles occur in eukaryotes, not prokaryotes. Compartments concentrate substrates and enzymes, maintain pH or ion conditions unlike the cytosol, and prevent incompatible reactions from interfering. The nuclear envelope separates transcription and RNA processing from translation. Lysosomes keep acid hydrolases away from cytoplasmic proteins. Compartmentalization increases control, although transport between compartments becomes essential.

A lysosome contains proteases, lipases, nucleases and carbohydrate-digesting enzymes whose optimum conditions are acidic. It fuses with vesicles containing worn organelles or engulfed particles, hydrolyses their macromolecules and returns reusable monomers to the cytosol. Describing a lysosome as a 'suicide packet' is incomplete: controlled recycling and defence are normal functions, while uncontrolled leakage is damaging.