Metabolism

Image:SantoriosMeal.jpg

Metabolism (from μεταβολισμος ("metabolismos")) is the biochemicalmodification of chemical compoundsin livingorganismsand cells. This includes the biosynthesisof complex organicmolecules(anabolism) and their breakdown (catabolism). Metabolism usually consists of sequences of enzymaticsteps, also called metabolic pathways. The total metabolismare all biochemical processes of an organism. The cell metabolismincludes all chemical processes in a cell. Without metabolism we would not be able to survive.

The term is derived from the Greekword for "change", or "overthrow" (Etymonline)).

Metabolic pathways

Important metabolic pathways are:

General pathways

• Carbohydrate metabolism
• Fatty acid metabolism
• Protein metabolism
• Nucleic Acid metabolism

Catabolism

Catabolicpathways that breakdown complex molecules into simple compounds:

• Cellular respiration, metabolic pathways that create energy (ATPand NADPH) from fuel molecules. These pathways are also involved in the digestionof food.
  • Carbohydrate catabolism
    • Glycogenolysis, the conversion of glycogeninto glucose.
    • Glycolysis, the conversion of glucose into pyruvateand ATP, does not require oxygen.
      • Embden-Meyerhof pathway, the common glycolysis pathway.
      • Entner-Doudoroff Pathway, an alternative glycolysis pathway in few bacteria.
    • Pentose phosphate pathway(hexose monophosphate shunt), generation of NADPH from glucose.
  • Protein catabolism, the hydrolysisof proteins into amino acids.
• Aerobic respiration
  • Electron transfer chain
  • Oxidative phosphorylation
• Anaerobic respiration,
  • Cori cycle
  • Lactic acid fermentation
  • Fermentation
  • Ethanol fermentation

Anabolism

Anabolicpathways that create building blocks and compounds from simple precursors:

• Glycogenesis
• Gluconeogenesis
• Porphyrinsynthesis pathway
• HMG-CoA reductase pathway, leading to cholesteroland isoprenoids.
• Secondary metabolism, metabolic pathways that are not essential for growth, development or reproduction, but that usually have ecologicalfunction.
• Photosynthesis
  • Light-dependent reaction(light reaction)
  • Light-independent reaction(dark reaction)
• Calvin cycle
• Carbon fixation

Drug metabolism

Drug metabolismpathways, the modification or degradation of drugsand other xenobioticcompounds through specialized enzyme systems:

• Cytochrome P450 oxidasesystem
• Flavin-containing monooxygenase system
• Alcohol metabolism

Nitrogen metabolism

Nitrogenmetabolism includes the pathways for turnover and excretionof nitrogen in organisms as well as the biological processes of the biogeochemicalnitrogen cycle:

• Urea cycle, important for excretion of nitrogen as urea.
• Biological nitrogen fixation
• Nitrogen assimilation
• Nitrification
• Denitrification

Other

• Human iron metabolism

History

The first controlled experiments in human metabolism were published by Santorio Santorioin 1614in 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

• Metabolomics
• Metabolome
• Metabolite
• Basal metabolic rate
• Thermic effect of food
• Iron-sulfur world theory, a "metabolism first" theory of the origin of life.
• Biodegradation

External links

• Interactive Flow Chart of the Major Metabolic Pathways
• Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology
• Boost Metabolism[Articles, information, exercise and diet tips to speed-up metabolism]
• 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 Genomesca:Metabolisme

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Metabolism Wikipedia article Metabolism.