Metabolism

Metabolic processes in human cells generate energy through the oxidation of molecules consumed in the diet and mediate the synthesis of diverse essential molecules not taken in the diet as well as the inactivation and elimination of toxic ones generated endogenously or present in the extracellular environment. The processes of energy metabolism can be classified into two groups according to whether they involve carbohydrate-derived or lipid-derived molecules, and within each group it is useful to distinguish processes that mediate the breakdown and oxidation of these molecules to yield energy from ones that mediate their synthesis and storage as internal energy reserves. Synthetic reactions are conveniently grouped by the chemical nature of the end products, such as nucleotides, amino acids and related molecules, and porphyrins. Detoxification reactions (biological oxidations) are likewise conveniently classified by the chemical nature of the toxin.<p>At the same time, all of these processes are tightly integrated. Intermediates in reactions of energy generation are starting materials for biosyntheses of amino acids and other compounds, broad-specificity oxidoreductase enzymes can be involved in both detoxification reactions and biosyntheses, and hormone-mediated signaling processes function to coordinate the operation of energy-generating and energy-storing reactions and to couple these to other biosynthetic processes.

人体细胞中的代谢过程通过氧化饮食中消耗的分子产生能量，并介导合成多种非饮食摄入的必需分子，以及内源生成或存在于细胞外环境中的有毒物质的失活和清除。根据涉及的是碳水化合物来源的分子还是脂质来源的分子，能量代谢过程可分为两组。在每个组内，区分介导这些分子分解和氧化以产生能量的过程与介导其合成和储存为内部能量储备的过程是有益的。根据最终产物的化学性质，合成反应可方便地分为核苷酸、氨基酸及相关分子和卟啉等。解毒反应（生物氧化）也便于根据毒素的化学性质进行分类。与此同时，所有这些过程都紧密整合在一起。能量生成反应的中间产物是氨基酸和其他化合物生物合成的起始材料，广谱氧化还原酶可参与解毒反应和生物合成，激素介导的信号传导过程则负责协调能量生成和储存反应的运作，并将这些过程与其他生物合成过程相耦合。