Other enzymes called phosphatases remove phosphate groups from enzymes. Phosphorylation and dephosphorylation regulate protein synthesis, cell division, activity of motor molecules, nuclear envelope breakdown, and development. Inhibition is common means by which cells regulate enzyme activity. In competitive inhibition, another molecule is similar to enzyme's substrate, competes with true substrate for enzyme's active site, resulting in decreased product formation. In noncompetitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.
Many enzymes require an inorganic ion or nonprotein cofactor to function.
Pathways of photosynthesis and aerobic respiration transform one form of energy into another. Without a constant input of solar energy, life could not exist. Photosynthesis uses energy to combine carbon dioxide and water to produce glucose. Aerobic respiration releases energy by breakdown of glucose to carbon dioxide and water. Both photosynthesis and respiration are metabolic pathways that use an electron transport system consisting of membrane-bound carriers to pass electrons from one carrier to another.