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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 desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. 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.

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 desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. 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.

新陈代谢的化学反应被组织成代谢途径，在代谢途径中，一种化学物质通过一系列步骤转化为另一种化学物质，每一步都由特定的’’’<font color=’’#ff8000’’>酶 enzyme </font>’’’来推动。酶对新陈代谢至关重要，因为它们通过将生物体与释放能量的自发反应耦合，使生物体能够驱动需要能量的理想反应，而这些反应本身不会发生。酶起催化剂的作用——它们使反应进行得更快——它们还可以调节代谢反应的速率，例如对细胞环境的变化或其他细胞发出的信号作出反应。

新陈代谢的化学反应被组织成代谢途径，在代谢途径中，一种化学物质通过一系列步骤转化为另一种化学物质，每一步都由特定的[[酶]]来推动。酶对新陈代谢至关重要，因为它们通过将生物体与释放能量的自发反应耦合，使生物体能够驱动需要能量的理想反应，而这些反应本身不会发生。酶起催化剂的作用——它们使反应进行得更快——它们还可以调节代谢反应的速率，例如对细胞环境的变化或其他细胞发出的信号作出反应。

The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The basal metabolic rate of an organism is the measure of the amount of energy consumed by all of these chemical reactions.

The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The basal metabolic rate of an organism is the measure of the amount of energy consumed by all of these chemical reactions.

A striking feature of metabolism is the similarity of the basic metabolic pathways among vastly different species. 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. These similarities in metabolic pathways are likely due to their early appearance in evolutionary history, and their retention because of their efficacy. 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.

A striking feature of metabolism is the similarity of the basic metabolic pathways among vastly different species. 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. These similarities in metabolic pathways are likely due to their early appearance in evolutionary history, and their retention because of their efficacy. 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.

新陈代谢的一个显著特征是，不同物种之间的基本新陈代谢途径具有相似性。例如，作为’’’<font color=’’#ff8000’’>三羧酸循环 citric acid cycle</font>’’’中的中间体，最著名的一组羧酸存在于所有已知的生物体中，它们在单细胞细菌’’’<font color=’’#ff8000’’>大肠杆菌 Escherichia coli</font>’’’和巨大的多细胞生物（如大象）中都能被找到。 这些代谢途径的相似性很可能是由于它们在演化史的早期出现，然后又因为它们的功效而保留下来。癌细胞的代谢也不同于正常细胞的代谢，这些差异可以用来寻找癌细胞治疗的靶点。

新陈代谢的一个显著特征是，不同物种之间的基本新陈代谢途径具有相似性。例如，作为[[三羧酸循环]]中的中间体，最著名的一组羧酸存在于所有已知的生物体中，它们在单细胞细菌[[大肠杆菌]]和巨大的多细胞生物（如大象）中都能被找到。 这些代谢途径的相似性很可能是由于它们在演化史的早期出现，然后又因为它们的功效而保留下来。癌细胞的代谢也不同于正常细胞的代谢，这些差异可以用来寻找癌细胞治疗的靶点。

Most of the structures that make up animals, plants and microbes are made from four basic classes of molecule: amino acids, carbohydrates , nucleic acid and lipids (often called fats). As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or by breaking them down and using them as a source of energy, by their digestion. These biochemicals can be joined together to make polymers such as DNA and proteins, essential macromolecules of life.

Most of the structures that make up animals, plants and microbes are made from four basic classes of molecule: amino acids, carbohydrates , nucleic acid and lipids (often called fats). As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or by breaking them down and using them as a source of energy, by their digestion. These biochemicals can be joined together to make polymers such as DNA and proteins, essential macromolecules of life.

构成动物、植物和微生物的大部分结构由四种基本分子组成: 氨基酸、糖类化合物、核酸和脂类(通常称为脂肪)。由于这些分子对生命至关重要，新陈代谢反应要么专注于在构建细胞和组织的过程中制造这些分子，要么将这些分子作为能量来源并将其消化分解。这些生化物质可以结合在一起形成DNA和蛋白质之类的聚合物，它们都是生命必不可少的’’’<font color=’’#ff8000’’> 大分子聚合物macromolecules</font>’’’。

构成动物、植物和微生物的大部分结构由四种基本分子组成: 氨基酸、糖类化合物、核酸和脂类(通常称为脂肪)。由于这些分子对生命至关重要，新陈代谢反应要么专注于在构建细胞和组织的过程中制造这些分子，要么将这些分子作为能量来源并将其消化分解。这些生化物质可以结合在一起形成DNA和蛋白质之类的聚合物，它们都是生命必不可少的[[大分子聚合物]]。

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Proteins are made of amino acids arranged in a linear chain joined together by peptide bonds. Many proteins are enzymes that catalyze the chemical reactions in metabolism. Other proteins have structural or mechanical functions, such as those that form the cytoskeleton, a system of scaffolding that maintains the cell shape. Proteins are also important in cell signaling, immune responses, cell adhesion, active transport across membranes, and the cell cycle. Amino acids also contribute to cellular energy metabolism by providing a carbon source for entry into the citric acid cycle (tricarboxylic acid cycle), especially when a primary source of energy, such as glucose, is scarce, or when cells undergo metabolic stress.

Proteins are made of amino acids arranged in a linear chain joined together by peptide bonds. Many proteins are enzymes that catalyze the chemical reactions in metabolism. Other proteins have structural or mechanical functions, such as those that form the cytoskeleton, a system of scaffolding that maintains the cell shape. Proteins are also important in cell signaling, immune responses, cell adhesion, active transport across membranes, and the cell cycle. Amino acids also contribute to cellular energy metabolism by providing a carbon source for entry into the citric acid cycle (tricarboxylic acid cycle), especially when a primary source of energy, such as glucose, is scarce, or when cells undergo metabolic stress.

蛋白质是由氨基酸组成的线性链，它们通过’’’<font color=’’#ff8000’’>肽键 peptide bonds</font>’’’连接在一起。许多蛋白质是在新陈代谢中催化化学反应的酶。其他蛋白质具有结构或机械功能，例如那些形成’’’<font color=’’#ff8000’’> 细胞骨架cytoskeleton</font>’’’的蛋白质（细胞骨架是维持细胞形状的支架系统）。蛋白质在’’’<font color=’’#ff8000’’>细胞信号传导 cell signaling</font>’’’、’’’<font color=’’#ff8000’’> 免疫反应immune responses</font>’’’、’’’<font color=’’#ff8000’’> 细胞粘附cell adhesion</font>’’’、主动跨膜转运和’’’<font color=’’#ff8000’’>细胞周期 cell cycle</font>’’’中也很重要。氨基酸还通过提供碳源进入细胞三羧酸循环，促进细胞的能量代谢，尤其是在’’’<font color=’’#ff8000’’>葡萄糖 glucose</font>’’’等主要能量来源匮乏或细胞发生代谢应激时。

蛋白质是由氨基酸组成的线性链，它们通过[[肽键]]连接在一起。许多蛋白质是在新陈代谢中催化化学反应的酶。其他蛋白质具有结构或机械功能，例如那些形成[[细胞骨架]]的蛋白质（细胞骨架是维持细胞形状的支架系统）。蛋白质在[[细胞信号传导]]、[[免疫反应]]、[[细胞粘附]]、主动跨膜转运和[[细胞周期]]中也很重要。氨基酸还通过提供碳源进入细胞三羧酸循环，促进细胞的能量代谢，尤其是在[[葡萄糖]]等主要能量来源匮乏或细胞发生代谢应激时。

Lipids are the most diverse group of biochemicals. Their main structural uses are as part of biological membranes both internal and external, such as the cell membrane, or as a source of energy. Lipids are usually defined as hydrophobic or amphipathic biological molecules but will dissolve in organic solvents such as alcohol, benzene or chloroform. The fats are a large group of compounds that contain fatty acids and glycerol; a glycerol molecule attached to three fatty acid esters is called a triacylglyceride. Several variations on this basic structure exist, including backbones such as sphingosine in the sphingomyelin, and hydrophilic groups such as phosphate as in phospholipids. Steroids such as sterol are another major class of lipids.

Lipids are the most diverse group of biochemicals. Their main structural uses are as part of biological membranes both internal and external, such as the cell membrane, or as a source of energy. Lipids are usually defined as hydrophobic or amphipathic biological molecules but will dissolve in organic solvents such as alcohol, benzene or chloroform. The fats are a large group of compounds that contain fatty acids and glycerol; a glycerol molecule attached to three fatty acid esters is called a triacylglyceride. Several variations on this basic structure exist, including backbones such as sphingosine in the sphingomyelin, and hydrophilic groups such as phosphate as in phospholipids. Steroids such as sterol are another major class of lipids.

脂类是最多样化的生物化学物质。它们的主要结构用途是作为’’’<font color=’’#ff8000’’> 生物膜biological membranes</font>’’’内部和外部的一部分，如’’’<font color=’’#ff8000’’> 细胞膜cell membrane</font>’’’，或作为能量来源。脂类通常被定义为疏水性或两亲性的生物分子，但会溶解在有机溶剂中，如酒精、苯或氯仿。脂肪是一大类含有脂肪酸和甘油的化合物，一个甘油分子连接到三个脂肪酸酯即称为三酰甘油酯。这种基本结构存在一些变异，包括主骨(如鞘磷脂中到鞘氨醇)和亲水基(如磷脂中的磷酸盐)。’’’<font color=’’#ff8000’’> 类固醇Steroids</font>’’’，如’’’<font color=’’#ff8000’’>固醇sterol </font>’’’，是另一类主要的脂类。

脂类是最多样化的生物化学物质。它们的主要结构用途是作为[[生物膜]]内部和外部的一部分，如[[细胞膜]]，或作为能量来源。脂类通常被定义为疏水性或两亲性的生物分子，但会溶解在有机溶剂中，如酒精、苯或氯仿。脂肪是一大类含有脂肪酸和甘油的化合物，一个甘油分子连接到三个脂肪酸酯即称为三酰甘油酯。这种基本结构存在一些变异，包括主骨(如鞘磷脂中到鞘氨醇)和亲水基(如磷脂中的磷酸盐)。[[类固醇]]，如[[固醇]]，是另一类主要的脂类。

The two nucleic acids, DNA and RNA, are polymers of nucleotides. Each nucleotide is composed of a phosphate attached to a ribose or deoxyribose sugar group which is attached to a nitrogenous base. Nucleic acids are critical for the storage and use of genetic information, and its interpretation through the processes of transcription and protein biosynthesis.This information is protected by DNA repair mechanisms and propagated through DNA replication. Many viruses have an RNA genome, such as HIV, which uses reverse transcription to create a DNA template from its viral RNA genome.RNA in ribozymes such as spliceosomes and ribosomes is similar to enzymes as it can catalyze chemical reactions. Individual nucleosides are made by attaching a nucleobase to a ribose sugar. These bases are heterocyclic rings containing nitrogen, classified as purines or pyrimidines. Nucleotides also act as coenzymes in metabolic-group-transfer reactions.

The two nucleic acids, DNA and RNA, are polymers of nucleotides. Each nucleotide is composed of a phosphate attached to a ribose or deoxyribose sugar group which is attached to a nitrogenous base. Nucleic acids are critical for the storage and use of genetic information, and its interpretation through the processes of transcription and protein biosynthesis.This information is protected by DNA repair mechanisms and propagated through DNA replication. Many viruses have an RNA genome, such as HIV, which uses reverse transcription to create a DNA template from its viral RNA genome.RNA in ribozymes such as spliceosomes and ribosomes is similar to enzymes as it can catalyze chemical reactions. Individual nucleosides are made by attaching a nucleobase to a ribose sugar. These bases are heterocyclic rings containing nitrogen, classified as purines or pyrimidines. Nucleotides also act as coenzymes in metabolic-group-transfer reactions.

A vitamin is an organic compound needed in small quantities that cannot be made in cells. In human nutrition, most vitamins function as coenzymes after modification; for example, all water-soluble vitamins are phosphorylated or are coupled to nucleotides when they are used in cells. Nicotinamide adenine dinucleotide (NAD⁺), a derivative of vitamin B₃ (niacin), is an important coenzyme that acts as a hydrogen acceptor. Hundreds of separate types of dehydrogenases remove electrons from their substrates and reduce NAD⁺ into NADH. This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to reduce their substrates. Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. The NAD⁺/NADH form is more important in catabolic reactions, while NADP⁺/NADPH is used in anabolic reactions.

A vitamin is an organic compound needed in small quantities that cannot be made in cells. In human nutrition, most vitamins function as coenzymes after modification; for example, all water-soluble vitamins are phosphorylated or are coupled to nucleotides when they are used in cells. Nicotinamide adenine dinucleotide (NAD⁺), a derivative of vitamin B₃ (niacin), is an important coenzyme that acts as a hydrogen acceptor. Hundreds of separate types of dehydrogenases remove electrons from their substrates and reduce NAD⁺ into NADH. This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to reduce their substrates. Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. The NAD⁺/NADH form is more important in catabolic reactions, while NADP⁺/NADPH is used in anabolic reactions.

’’’<font color=’’#ff8000’’>维生素 vitamin </font>’’’是一类细胞不能合成的微量有机化合物。在人体营养中，大多数维生素经过修饰后都具有辅酶的功能，例如，所有水溶性维生素在细胞中使用时都会被磷酸化或与核苷酸偶联。’’’<font color=’’#ff8000’’>烟酰胺腺嘌呤二核苷酸 Nicotinamide adenine dinucleotide</font>’’’(NAD⁺)是维生素B₃(烟酸)的衍生物，它是一种重要的辅酶，起着氢接受器的作用。数百种不同类型的脱氢酶从其底物中去除电子，并将NAD<sub>+</sup>还原成NADH。这种还原形式的辅酶是细胞中任何需要还原其底物的还原酶的底物。烟酰胺腺嘌呤二核苷酸在细胞中以两种相关形式存在，即NADH和NADPH。NAD < sup > + </sup >/NADH 形式在分解代谢反应中起重要作用，而 NADP < sup > + </sup >/NADPH 形式在分解代谢反应中起重要作用。

[[维生素]]是一类细胞不能合成的微量有机化合物。在人体营养中，大多数维生素经过修饰后都具有辅酶的功能，例如，所有水溶性维生素在细胞中使用时都会被磷酸化或与核苷酸偶联。[[烟酰胺腺嘌呤二核苷酸]](NAD⁺)是维生素B₃(烟酸)的衍生物，它是一种重要的辅酶，起着氢接受器的作用。数百种不同类型的脱氢酶从其底物中去除电子，并将NAD<sub>+</sup>还原成NADH。这种还原形式的辅酶是细胞中任何需要还原其底物的还原酶的底物。烟酰胺腺嘌呤二核苷酸在细胞中以两种相关形式存在，即NADH和NADPH。NAD < sup > + </sup >/NADH 形式在分解代谢反应中起重要作用，而 NADP < sup > + </sup >/NADPH 形式在分解代谢反应中起重要作用。

The structure of iron-containing [[hemoglobin. The protein subunits are in red and blue, and the iron-containing heme groups in green. From .]]

The structure of iron-containing [[hemoglobin. The protein subunits are in red and blue, and the iron-containing heme groups in green. From .]]

含铁’’’<font color=’’#ff8000’’>血红蛋白 hemoglobin</font>’’’的结构。蛋白质亚基为红色和蓝色，含铁血红素基为绿色。

含铁[[血红蛋白]]的结构。蛋白质亚基为红色和蓝色，含铁血红素基为绿色。

The abundant inorganic elements act as electrolytes. The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate and the organic ion bicarbonate. The maintenance of precise ion gradients across cell membranes maintains osmotic pressure and pH. Ions are also critical for nerve and muscle function, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cell's fluid, the cytosol. Electrolytes enter and leave cells through proteins in the cell membrane called ion channels. For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules.

The abundant inorganic elements act as electrolytes. The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate and the organic ion bicarbonate. The maintenance of precise ion gradients across cell membranes maintains osmotic pressure and pH. Ions are also critical for nerve and muscle function, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cell's fluid, the cytosol. Electrolytes enter and leave cells through proteins in the cell membrane called ion channels. For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules.

丰富的无机元用作电解质。最重要的离子是钠、钾、钙、镁、氯化物、磷酸盐和有机离子重碳酸盐。维持细胞膜上精确的离子梯度可以维持’’’<font color=’’#ff8000’’>渗透压 osmotic pressure</font>’’’和 ph 值。离子对于神经和肌肉功能也是至关重要的，因为这些组织中的动作电位是由细胞外液和细胞液之间的电解质交换产生的。电解质通过细胞膜上称为离子通道的蛋白质进入和离开细胞。例如，肌肉收缩依赖于钙、钠和钾通过细胞膜和T管中的离子通道的运动。

丰富的无机元用作电解质。最重要的离子是钠、钾、钙、镁、氯化物、磷酸盐和有机离子重碳酸盐。维持细胞膜上精确的离子梯度可以维持[[渗透压]]和 ph 值。离子对于神经和肌肉功能也是至关重要的，因为这些组织中的动作电位是由细胞外液和细胞液之间的电解质交换产生的。电解质通过细胞膜上称为离子通道的蛋白质进入和离开细胞。例如，肌肉收缩依赖于钙、钠和钾通过细胞膜和T管中的离子通道的运动。

Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. Carbohydrates are usually taken into cells once they have been digested into monosaccharides. Once inside, the major route of breakdown is glycolysis, where sugars such as glucose and fructose are converted into pyruvate and some ATP is generated. Pyruvate is an intermediate in several metabolic pathways, but the majority is converted to acetyl-CoA through aerobic (with oxygen) glycolysis and fed into the citric acid cycle. Although some more ATP is generated in the citric acid cycle, the most important product is NADH, which is made from NAD⁺ as the acetyl-CoA is oxidized. This oxidation releases carbon dioxide as a waste product. In anaerobic conditions, glycolysis produces lactate, through the enzyme lactate dehydrogenase re-oxidizing NADH to NAD+ for re-use in glycolysis. An alternative route for glucose breakdown is the pentose phosphate pathway, which reduces the coenzyme NADPH and produces pentose sugars such as ribose, the sugar component of nucleic acids.

Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. Carbohydrates are usually taken into cells once they have been digested into monosaccharides. Once inside, the major route of breakdown is glycolysis, where sugars such as glucose and fructose are converted into pyruvate and some ATP is generated. Pyruvate is an intermediate in several metabolic pathways, but the majority is converted to acetyl-CoA through aerobic (with oxygen) glycolysis and fed into the citric acid cycle. Although some more ATP is generated in the citric acid cycle, the most important product is NADH, which is made from NAD⁺ as the acetyl-CoA is oxidized. This oxidation releases carbon dioxide as a waste product. In anaerobic conditions, glycolysis produces lactate, through the enzyme lactate dehydrogenase re-oxidizing NADH to NAD+ for re-use in glycolysis. An alternative route for glucose breakdown is the pentose phosphate pathway, which reduces the coenzyme NADPH and produces pentose sugars such as ribose, the sugar component of nucleic acids.

碳水化合物分解代谢是将碳水化合物分解成较小的单位的过程。碳水化合物一旦被消化成单糖，通常就被带入细胞。一旦进入细胞内，分解的主要途径就是糖酵解，其中糖（例如葡萄糖和果糖）被转化为丙酮酸并生成一些ATP。丙酮酸是几种代谢途径中的中间体，但大多数通过有氧（含氧）糖酵解转化为乙酰辅酶 a 并进入三羧酸循环。尽管在三羧酸循环中会产生更多的ATP，但最重要的产物是NADH，它是由 NAD < sup > + </sup > 在乙酰辅酶A被氧化后制成的。这种氧化释放出作为废物的二氧化碳。在厌氧条件下，糖酵解产生乳酸盐，即由乳酸脱氢酶将丙酮酸盐转化为乳酸盐，同时将NADH重新氧化为NAD < sup > + </sup > 再用于糖酵解。葡萄糖分解的另一种途径是磷酸戊糖途径，它还原辅酶NADPH并产生戊糖，如核糖（核酸的糖成分）。

碳水化合物分解代谢是将碳水化合物分解成较小的单位的过程。碳水化合物一旦被消化成单糖，通常就被带入细胞。一旦进入细胞内，分解的主要途径就是糖酵解，其中糖（例如葡萄糖和果糖）被转化为丙酮酸并生成一些ATP。丙酮酸是几种代谢途径中的中间体，但大多数通过有氧（含氧）糖酵解转化为乙酰辅酶A并进入三羧酸循环。尽管在三羧酸循环中会产生更多的ATP，但最重要的产物是NADH，它是由 NAD < sup > + </sup > 在乙酰辅酶A被氧化后制成的。这种氧化释放出作为废物的二氧化碳。在厌氧条件下，糖酵解产生乳酸盐，即由乳酸脱氢酶将丙酮酸盐转化为乳酸盐，同时将NADH重新氧化为NAD < sup > + </sup > 再用于糖酵解。葡萄糖分解的另一种途径是磷酸戊糖途径，它还原辅酶NADPH并产生戊糖，如核糖（核酸的糖成分）。

Fats are catabolised by [[hydrolysis]] to free fatty acids and glycerol. The glycerol enters glycolysis and the fatty acids are broken down by [[beta oxidation]] to release acetyl-CoA, which then is fed into the citric acid cycle. Fatty acids release more energy upon oxidation than carbohydrates because carbohydrates contain more oxygen in their structures. Steroids are also broken down by some bacteria in a process similar to beta oxidation, and this breakdown process involves the release of significant amounts of acetyl-CoA, propionyl-CoA, and pyruvate, which can all be used by the cell for energy. ''M. tuberculosis'' can also grow on the lipid [[cholesterol]] as a sole source of carbon, and genes involved in the cholesterol use pathway(s) have been validated as important during various stages of the infection lifecycle of ''M. tuberculosis''.<ref>{{cite journal | vauthors = Wipperman MF, Sampson NS, Thomas ST | title = Pathogen roid rage: cholesterol utilization by Mycobacterium tuberculosis | journal = Critical Reviews in Biochemistry and Molecular Biology | volume = 49 | issue = 4 | pages = 269–93 | date = 2014 | pmid = 24611808 | pmc = 4255906 | doi = 10.3109/10409238.2014.895700 }}</ref>

Fats are catabolised by [[hydrolysis]] to free fatty acids and glycerol. The glycerol enters glycolysis and the fatty acids are broken down by [[beta oxidation]] to release acetyl-CoA, which then is fed into the citric acid cycle. Fatty acids release more energy upon oxidation than carbohydrates because carbohydrates contain more oxygen in their structures. Steroids are also broken down by some bacteria in a process similar to beta oxidation, and this breakdown process involves the release of significant amounts of acetyl-CoA, propionyl-CoA, and pyruvate, which can all be used by the cell for energy. ''M. tuberculosis'' can also grow on the lipid [[cholesterol]] as a sole source of carbon, and genes involved in the cholesterol use pathway(s) have been validated as important during various stages of the infection lifecycle of ''M. tuberculosis''.<ref>{{cite journal | vauthors = Wipperman MF, Sampson NS, Thomas ST | title = Pathogen roid rage: cholesterol utilization by Mycobacterium tuberculosis | journal = Critical Reviews in Biochemistry and Molecular Biology | volume = 49 | issue = 4 | pages = 269–93 | date = 2014 | pmid = 24611808 | pmc = 4255906 | doi = 10.3109/10409238.2014.895700 }}</ref>

In plants, algae, and cyanobacteria, photosystem II uses light energy to remove electrons from water, releasing oxygen as a waste product. The electrons then flow to the cytochrome b6f complex, which uses their energy to pump protons across the thylakoid membrane in the chloroplast. These protons move back through the membrane as they drive the ATP synthase, as before. The electrons then flow through photosystem I and can then either be used to reduce the coenzyme NADP< sup > + </sup > .fThese cooenzyme can be used in the Calvin cycle, which is discussed below, or recycled for further ATP generation.

In plants, algae, and cyanobacteria, photosystem II uses light energy to remove electrons from water, releasing oxygen as a waste product. The electrons then flow to the cytochrome b6f complex, which uses their energy to pump protons across the thylakoid membrane in the chloroplast. These protons move back through the membrane as they drive the ATP synthase, as before. The electrons then flow through photosystem I and can then either be used to reduce the coenzyme NADP< sup > + </sup > .fThese cooenzyme can be used in the Calvin cycle, which is discussed below, or recycled for further ATP generation.

在植物、藻类和蓝藻中，光系统 II 利用光能将电子从水中移走，释放出氧气。然后电子流向细胞色素b6f蛋白复合体，后者利用它们的能量穿过叶绿体中的类囊体膜，泵入质子。这些质子在驱动ATP合成酶时通过膜向后移动，就像之前一样。然后电子流经光系统I，可以用来减少辅酶NADP< sup > + </sup >。这些辅酶可用于’’’<font color=’’#ff8000’’> 卡尔文循环Calvin cycle</font>’’’(下文将对此进行讨论)，或被循环用于进一步生成ATP。

在植物、藻类和蓝藻中，光系统 II 利用光能将电子从水中移走，释放出氧气。然后电子流向细胞色素b6f蛋白复合体，后者利用它们的能量穿过叶绿体中的类囊体膜，泵入质子。这些质子在驱动ATP合成酶时通过膜向后移动，就像之前一样。然后电子流经光系统I，可以用来减少辅酶NADP< sup > + </sup >。这些辅酶可用于[[卡尔文循环]](下文将对此进行讨论)，或被循环用于进一步生成ATP。

==Anabolism==

==Anabolism==