Everything about Catabolism totally explained
» For the related metabolic process, see anabolism.
Catabolism is the set of
metabolic pathways which break down molecules into smaller units and release
energy. In catabolism, large molecules such as
polysaccharides,
fatty acids,
nucleic acids and
proteins are broken down into smaller units such as
monosaccharides,
fatty acids,
nucleotides and
amino acids, respectively. As molecules such as polysaccharides, proteins and nucleic acids are made from long chains of these small
monomer units, the large molecules are called
polymers.
Cells use the
monomers released from breaking down polymers to either construct new polymer molecules, or degrade the monomers further to simple waste products, releasing energy. Cellular wastes include
lactic acid,
acetic acid,
carbon dioxide,
ammonia, and
urea. The creation of these wastes is usually an
oxidation process involving a release of chemical free energy, some of which is lost as
heat, but the rest is used to drive the synthesis of
adenosine triphosphate (ATP). This molecule acts as a way for the cell to transfer the energy released by catabolism to the energy-requiring reactions which make up
anabolism. Catabolism therefore provides the chemical energy necessary for the maintenance and growth of cells. Examples of catabolic processes include
glycolysis, the
citric acid cycle, the breakdown of muscle protein in order to use amino acids as
substrates for
gluconeogenesis and breakdown of
fat in
adipose tissue to
fatty acids.
There are many signals which control catabolism. 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, depending on which part of metabolism they stimulate. The "classic" catabolic hormones known since the early 20th century are
cortisol,
glucagon, and
adrenaline (and other
catecholamines). In recent decades, many more hormones with at least some catabolic effects have been discovered, including
cytokines,
orexin and
hypocretin (a hormone pair), and
melatonin.
Further Information
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