Anabolism

Anabolism is the metabolic process that builds larger molecules from smaller ones. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or 'catabolic', which is the opposite.

Anabolic pathways usually require energy (provided by ATP hydrolysis and reducing power (most often donated by NADPH). These pathways are needed in order to produce growth, differentiation and eventually proliferation of of cells. Examples of complex anabolic processes include growth and mineralization of bone and increase of muscle mass.

Because it is counterproductive to have anabolic and catabolic processes occurring in cells simultaneously, there are many signals that switch on anabolic processes while switching off catabolic processes and vice versa. Most of the known signals are hormones and the molecules involved in metabolism itself. Endocrinologists have traditionally classified many of the hormones as anabolic or catabolic.

Anabolic Pathways

• Glycogenesis
• Gluconeogenesis
• Porphyrin synthesis pathway
• HMG-CoA reductase pathway, leading to cholesterol and isoprenoids.
• Secondary metabolism, metabolic pathways that are not essential for growth, development or reproduction, but that usually have ecological function.
• Photosynthesis
  • Light-dependent reaction (light reaction)
  • Light-independent reaction (dark reaction)
• Calvin cycle
• Carbon fixation
• Glyoxylate cycle
• Fatty acid synthesis

Classic Anabolic Hormones

• Growth hormone
• IGF1 and other insulin-like growth factors
• Insulin
• Testosterone
• Estrogen

Newer hormones associated with the balance of the catabolic and anabolic states include

• Orexin (also called Hypocretin), made by nerve cells in the hypothalamus
• Melatonin, produced by cells in the pineal gland