Metabolism
Metabolism encompasses all chemical reactions sustaining life.
Metabolism refers to the set of life-sustaining chemical reactions that occur within living organisms. The three main functions of metabolism are the conversion of energy in food into a usable form for cellular processes; the conversion of food to building blocks of macromolecules such as proteins, lipids, nucleic acids, and some carbohydrates; and the excretion of metabolic wastes. These enzyme-catalyzed reactions allow organisms to grow, reproduce, maintain their structures, and respond to their environments.
- field
- Biochemistry
- known_for
- Set of life-sustaining chemical reactions in organisms
- key_functions
- Energy conversion, biosynthesis of macromolecules, waste excretion
- types
- Catabolism (breaking down) and anabolism (building up)
- key_molecules
- Amino acids, carbohydrates, nucleic acids, lipids
- central_coenzyme
- Adenosine triphosphate (ATP)
Lore & Background
Metabolic reactions may be categorized as catabolic—the breaking down of compounds (for example, of glucose to pyruvate by cellular respiration); or anabolic—the building up (biosynthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy, and anabolism consumes energy. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. Enzymes are crucial to metabolism because they allow organisms to drive reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release energy.
Reader's Guide
Metabolism is fundamental to all living organisms, determining which substances are nutritious and which are poisonous. A notable feature is the similarity of basic metabolic pathways among vastly different species, such as the citric acid cycle intermediates found in both the bacterium Escherichia coli and elephants. These similarities are likely due to their early appearance in evolutionary history and retention due to efficacy. In various diseases, such as type II diabetes, metabolic syndrome, and cancer, normal metabolism is disrupted. The metabolism of cancer cells differs from normal cells, and these differences can be used to find targets for therapeutic intervention. The basal metabolic rate measures the amount of energy consumed by all chemical reactions in an organism. Coenzymes like ATP and NAD+ are central to transferring energy and chemical groups between reactions, with vitamins often functioning as coenzymes after modification.
Did You Know?
- The word metabolism comes from Greek μεταβολή (metabolē) meaning 'change'.
- Some prokaryotes use hydrogen sulfide (H₂S) as a nutrient, though it is poisonous to some animals.
- The human body can use about its own weight in ATP per day, as it is continuously regenerated.
- All water-soluble vitamins are phosphorylated or coupled to nucleotides when used in cells.
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