When 1 phosphate group is broken off ATP, adenosine diphosphate, that is, ADP, and a free phosphate groups result, and energy is available. Yet the ADP still has two phosphate groups, and in times of energy need, a cell can still snip another phosphate off ADP to form adenosine monophosphate, or AMP and some energy. Cyclic AMP, cAMP . Sometimes ATP is directly converted to a cyclic form of AMP called cyclic AMP, or cAMP, and a diphosphate group is directly removed from ATP in the process. The sum of all the chemical reactions occurring in a cell, many of which are for breaking down nutrients, many of which are for building other molecules, is called cell metabolism .
Metabolism involves both catabolism, and anabolism.
Catabolism is the breaking down of complex molecules to more simple molecules. It is performed by cell enzymes in order to extract covalent bond energy. Metabolic pathways that have been studied in cells include glycolysis , fermentation , cell respiration , the electron transport chain , and beta-oxidation of fatty acids . Gluconeogenesis is the reverse of glycolysis, where glucose is created from raw ingredients such as amino acids and portions of various other molecules. Glucose for glycolysis comes from the blood, where it enters most cells under the auspices of insulin hormone.