![]() ![]() Lipids are the polymers of fatty acids that contain a long, non-polar hydrocarbon chain with a small polar region containing oxygen. Their main structural uses are as part of biological membranes both internal and external, such as the cell membrane. Lipids are the most diverse group of biochemicals. These biochemicals can be joined to make polymers such as DNA and proteins, essential macromolecules of life. As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or on breaking them down and using them to obtain energy, by their digestion. Most of the structures that make up animals, plants and microbes are made from four basic classes of molecules: amino acids, carbohydrates, nucleic acid and lipids (often called fats). Key biochemicals įurther information: Biomolecule, Cell (biology), and Biochemistry Structure of a triacylglycerol lipid This is a diagram depicting a large set of human metabolic pathways. The metabolism of cancer cells is also different from the metabolism of normal cells, and these differences can be used to find targets for therapeutic intervention in cancer. In various diseases, such as type II diabetes, metabolic syndrome, and cancer, normal metabolism is disrupted. These similarities in metabolic pathways are likely due to their early appearance in evolutionary history, and their retention is likely due to their efficacy. For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all known organisms, being found in species as diverse as the unicellular bacterium Escherichia coli and huge multicellular organisms like elephants. The basal metabolic rate of an organism is the measure of the amount of energy consumed by all of these chemical reactions.Ī striking feature of metabolism is the similarity of the basic metabolic pathways among vastly different species. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous. Enzymes act as catalysts – they allow a reaction to proceed more rapidly – and they also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell's environment or to signals from other cells. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release 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. Usually, catabolism releases energy, and anabolism consumes energy. 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 ( synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). ![]() The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transportation of substances into and between different cells, in which case the above described set of reactions within the cells is called intermediary (or intermediate) metabolism. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes the conversion of food to building blocks for proteins, lipids, nucleic acids, and some carbohydrates and the elimination of metabolic wastes. Metabolism ( / m ə ˈ t æ b ə l ɪ z ə m/, from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical reactions in organisms.
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