Metabolism
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Metabolism (from μεταβολισμος ("metabolismos")) is the biochemical modification of chemical compounds in living organisms and cells. This includes the biosynthesis of complex organic molecules (anabolism) and their breakdown (catabolism). Metabolism usually consists of sequences of enzymatic steps, also called metabolic pathways. The total metabolism are all biochemical processes of an organism. The cell metabolism includes all chemical processes in a cell.The Dynamic Energy Budget theory aims to quantify the metabolic organisation of individual organisms; many species are unicellular.
The term is derived from the Greek word for "change", or "overthrow" ([Etymonline])).
Metabolic pathways
Important metabolic pathways are:General pathways
- Carbohydrate metabolism
- Fatty acid metabolism
- Protein metabolism
- Nucleic Acid metabolism
Anabolism
Anabolic pathways that create building blocks and compounds from simple precursors:- 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
Catabolism
Drug metabolism
Drug metabolism pathways, the modification or degradation of drugs and other xenobiotic compounds through specialized enzyme systems:Nitrogen metabolism
Nitrogen metabolism includes the pathways for turnover and excretion of nitrogen in organisms as well as the biological processes of the biogeochemical nitrogen cycle:- Urea cycle, important for excretion of nitrogen as urea.
- Biological nitrogen fixation
- Nitrogen assimilation
- Nitrification
- Denitrification
Other
History
The first controlled experiments in human metabolism were published by Santorio Santorio in 1614 in his book Ars de statica medecina that made him famous throughout Europe. He describes his long series of experiments in which he weighed himself in a chair suspended from a steelyard balance (see image), before and after eating, sleeping, working, sex, fasting, depriving from drinking, and excreting. He found that by far the greatest part of the food he took in was lost from the body through perspiratio insensibilis (insensible perspiration).
See also
- Cell metabolism
- Metabolomics
- Metabolome
- Metabolite
- Basal metabolic rate
- Thermic effect of food
- Iron-sulfur world theory, a "metabolism first" theory of the origin of life.
- Biodegradation
- Calorimetry
- Respirometry
- Microbial metabolism
External links
- [Interactive Flow Chart of the Major Metabolic Pathways]
- [Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology]
- [The Biochemistry of Metabolism at Rensselaer Polytechnic Institute]
- [Flow Chart of Metabolic Pathways at ExPASy]
- [Santorio Santorio's experiments]
- [KEGG: Kyoto Encyclopedia of Genes and Genomes]
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