User:HeatherKJ4/sandbox

= Anabolism = From Wikipedia, the free encyclopedia

Anabolism (from Greek: ἁνά, "upward" and βάλλειν, "to throw", also called biosynthesis) is the set of metabolic pathways that construct molecules from smaller units utilizing the energy released by catabolism. These reactions require energy, known also as an endergonic process. One way of categorizing metabolic processes, whether at the cellular, organ or organism level, is as "anabolic" or as "catabolic", which is the opposite and thus the separation of a macromolecule. Anabolism operates with separate enzymes from catalysis, which undergo irreversible steps at some point in their pathways. This allows the cell to regulate the rate of production and prevent an infinite loop from forming with catabolism. Endocrinologists have traditionally classified hormones as anabolic or catabolic, depending on which part of metabolism they stimulate.

Pathway
Macromolecules are created from smaller molecules using enzymes and cofactors. The starting materials, called the precursor molecules, can be joined together using chemical energy from the energetically favorable dephosphorylation of ATP, the reductive energy of the cofactors NADH, NADPH, and FADH2, or other favorable side reactions. Anabolism usually involves reduction and decreases entropy, making it unfavorable without energy input. Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the hydrolysis of adenosine triphosphate (ATP). The reducing agents NADH, NADPH, and FADH2, as well as metal ions, also act as cofactors at various steps in the anabolic pathways like fatty acid synthesis and photosynthesis. Anabolism can also be driven by enthalpy without energy input in cases like the formation of the phospholipid bilayer of a cell, where hydrophobic interactions aggregate the molecules.

Photosynthesis
Photosynthesis in plants and certain bacteria is an anabolic process that produces the monomer glucose from CO2 and H2O. Polymerization, an anabolic pathway used to build macromolecules such as nucleic acids, proteins, and polysaccharides, uses condensation reactions to join monomers.

In Humans
Anabolic processes also tend toward building up organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules. Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass. The classic anabolic hormones are the anabolic steroids, which stimulate protein synthesis and muscle growth, and insulin.

Gluconeogenesis
Glucagon is traditionally a catabolic hormone, but also stimulates the anabolic process of gluconeogenesis by the liver, and to a lesser extent the kidney cortex and intestines, during starvation to prevent hypoglycemia.

Regulation
The balance between anabolism and catabolism is also regulated by circadian rhythms, with processes such as glucose metabolism fluctuating to match an animal's normal periods of activity throughout the day.