Cell Metabolism

Metabolism is all the chemical reactions in a cell. Most happen as metabolic pathways — chains of reactions where each step is controlled by a specific enzyme.

A metabolic pathway: each step needs its own enzyme and passes through intermediates.

In a pathway there are many regulated steps, each producing intermediate compounds, each needing a specific enzyme, and each losing some energy as heat.

Internal membranes matter

Folded internal membranes pack in surface area for these reactions: the cristae of mitochondria and the thylakoid (grana) stacks of chloroplasts hold the enzymes for respiration and photosynthesis.

Chemicals can interfere with metabolism — some harmful (cyanide blocks respiration; herbicides, insecticides), some useful (antibiotics target bacterial enzymes). Weighing benefit against harm is a real-world judgement.