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6: Metabolism

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    • 6.1: Metabolism - Sugars
    • 6.2: Citric Acid Cycle & Related Pathways
      The primary catabolic pathway in the body is the citric acid cycle because it is here that oxidation to carbon dioxide occurs for breakdown products of the cell’s major building blocks - sugars, fatty acids, and amino acids. The pathway is cyclic and thus, does not really have a starting or ending point. All of the reactions occur in mitochondria, though one enzyme is embedded in the organelle’s inner membrane. Cells may use a subset of the reactions of the cycle to produce a desired molecule.
    • 6.3: Fats and Fatty Acids
      There is a tremendous amount of interest in the metabolism of fat and fatty acids. Fat is the most important energy storage form of animals, storing considerably more energy per carbon than carbohydrates, but its insolubility in water requires the body to package it specially for transport. Surprisingly, fat/fatty acid metabolism is not nearly as tightly regulated as that of carbohydrates. Neither are the metabolic pathways of breakdown and synthesis particularly complicated, either.
    • 6.4: Other Lipids
      Sugars are the building blocks of carbohydrates, amino acids are the building blocks of proteins and nucleotides are the building blocks of the nucleic acids - DNA and RNA. Another crucial building block is acetyl-CoA, which is used to build many lipid substances, including fatty acids, cholesterol, fat soluble vitamins, steroid hormones, prostaglandins, endocannabinoids, and the bile acids. Indeed, acetyl-CoA goes into more different classes of molecule than any other building block.
    • 6.5: Amino Acids and the Urea Cycle
      In contrast to some of the metabolic pathways described to this point, amino acid metabolism is not a single pathway. The 20 amino acids have some parts of their metabolism that overlap with each other, but others are very different from the rest. In discussing amino acid metabolism, we will group metabolic pathways according to common metabolic features they possess (where possible).
    • 6.6: Nucleotides
      Nucleotides are most often thought of as the building blocks of the nucleic acids, DNA and RNA. While this, is, of course, a vital function, nucleotides also play other important roles in cells. Ribonucleoside triphosphates like ATP, CTP, GTP and UTP are necessary, not just for the synthesis of RNA, but as part of activated intermediates like UDP-glucose in biosynthetic pathways. ATP is also the universal “energy currency” of cells.

    Thumbnail: Metabolic Metro Map. Image used with permission (CC BY-SA 4.0; Chakazul).​​​​​

    6: Metabolism is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Kevin Ahern, Indira Rajagopal, & Taralyn Tan.

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