Cells and Enzymes

All animal cells have four main parts; the nucleus, cytoplasm, mitochondria and the cell membrane (cell wall). The nucleus contains DNA which carries the instructions for making proteins. Inside the cytoplasm proteins are made and some other reactions take place. Inside the mitochondria the reactions of aerobic respiration take place.

Bacteria cells are different because they don't have a nucleus. Instead of a nucleus they just have a circular molecule of DNA.

Enzymes are proteins that speed up the chemical reactions taking place inside cells. Enzymes are catalysts because they speed up reactions. The 'lock and key' model is a theory that explains how an enzyme joins with the substrate at the active site.