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6: Metabolism II – Anabolic Reactions

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    As pointed out at the beginning of this book, most of the energy for life on this planet originates from the sun. In the last chapter, the discussion was on the breakdown of complex molecules such as sugars and fats that hold great, but difficult to access, potential energy to produce molecules like ATP that can act as more readily accessible sources of cellular energy. This energy is then used to synthesize the more complex biomolecules necessary to build living cells. That synthesis, the formation of sugars, fatty acids, and amino acids, is the focus of this chapter. Although technically the polymerization of nucleic acids and proteins are anabolic processes, they are not included in this chapter and are examined in detail separately.

    • 6.1: Photosynthesis
      This page covers photosynthesis, detailing how plants convert solar energy into chemical energy through sunlight absorption by pigments in chloroplasts. It explores the light-dependent reactions that produce ATP and NADPH and the light-independent reactions that synthesize sugars. Key processes, such as the role of the oxygen-evolving complex in stabilizing water and the pathways of electron flow, are explained, emphasizing their importance in powering ATP synthase.
    • 6.2: The Calvin Cycle
      This page discusses carbon fixation in plants, focusing on the Calvin cycle in C3 plants, where rubisco fixes CO2 but can incur energy costs through photorespiration. C4 plants utilize PEP carboxylase to enhance efficiency in hot climates, while desert plants employ Crassulacean Acid Metabolism (CAM) to fix CO2 at night, conserving water during daytime.
    • 6.3: The Pentose Phosphate Pathway
      This page discusses the importance of NADPH, a reducing agent in cellular metabolism found in both plants and animals. It emphasizes its role in the pentose phosphate pathway (PPP), where glucose-6-phosphate is converted to ribulose-5-phosphate, generating NADPH. Ribulose-5-phosphate is essential for nucleotide synthesis and various metabolic functions.
    • 6.4: Gluconeogenesis
      This page covers gluconeogenesis, detailing the synthesis of glucose from pyruvate and glycolytic/TCA intermediates. It explains differences in animal and plant pathways for converting acetyl-CoA to oxaloacetate, noting animals' lack of a direct route. The page highlights key glycolytic enzymes and unique regulations of gluconeogenic enzymes.
    • 6.5: Glycogen Synthesis
      This page discusses glucose as the primary energy source for cells and its inefficiency for long-term storage. To enhance storage, animals convert glucose to glycogen through specific glycosidic linkages, starting with UDP-glucose. The synthesis involves glycogenin and glycogen synthase, with branching facilitated by a specific enzyme.
    • 6.6: Fatty Acid Synthesis
      This page explains fatty acid synthesis, which occurs in the cytoplasm via fatty acid synthase, producing palmitic acid from acetyl-CoA and malonyl-CoA. It highlights the need for dietary linoleic acid in vertebrates due to their inability to perform certain desaturations. Additionally, it covers triacylglycerol synthesis, involving reactions between fatty acyl-CoA and glycerol-3-phosphate, with energy produced through ATP hydrolysis.
    • 6.7: Amino Acid Synthesis
      This page covers the synthesis of nonessential amino acids in humans, focusing on key pathways and enzymes. It highlights glutamate as a nitrogen donor for amino acids like glutamine, proline, alanine, and aspartate. Additionally, it explains serine's synthesis from 3-phosphoglycerate and its role in producing glycine and cysteine, along with tyrosine's dependence on phenylalanine.

    Thumbnail: Biochemical processes that break things down from larger to smaller are called catabolic processes. Catabolic processes are often oxidative in nature and energy releasing. Some, but not all of that energy is captured as ATP. (CC BY-SA-NC; Kevin Ahern & Indira Rajagopal).

    This page titled 6: Metabolism II – Anabolic Reactions is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by E. V. Wong via source content that was edited to the style and standards of the LibreTexts platform.