Science Fair Project Encyclopedia
Metabolism (from μεταβολισμος (metabolismos), the Greek word for "change"), 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.
Important metabolic pathways are:
- Carbohydrate metabolism
- Fatty acid metabolism
- Citric acid cycle (Krebs cycle, tricarboxylic acid cycle)
Catabolic pathways that breakdown complex molecules into simple compounds:
- Cellular respiration, metabolic pathways that create energy (ATP and NADPH) from fuel molecules. These pathways are also involved in the digestion of food.
- Carbohydrate catabolism
- Glycogenolysis, the conversion of glycogen into glucose.
- Glycolysis, the conversion of glucose into pyruvate and ATP, does not require oxygen.
- Pentose phosphate pathway (hexose monophosphate shunt), generation of NADPH from glucose.
- Protein catabolism, the hydrolysis of proteins into amino acids.
- Aerobic respiration
- Anaerobic respiration,
- Carbohydrate catabolism
Anabolic pathways that create building blocks and compounds from simple precursors:
- 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.
- Urea cycle, important for excretion of nitrogen as urea.
- Biological nitrogen fixation
- Nitrogen assimilation
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, making love, 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).
- Basal metabolic rate
- Thermic effect of food
- Iron-sulfur world theory, a "metabolism first" theory of the origin of life.
- Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology
- Santorio Santorio's experiments
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