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{{Biochemistry sidebar}}

[[File:Metabolism.png|thumb|Simplified view of the cellular metabolism]]

[[File:Metabolism.png|thumb|细胞新陈代谢的简化图]]

The metabolic system of a particular organism determines which substances it will find [[nutrition|nutritious]] and which [[poison]]ous. For example, some [[prokaryote]]s use [[hydrogen sulfide]] as a nutrient, yet this gas is poisonous to animals.<ref name="Physiology1">{{cite book |author=Friedrich C |title=Physiology and genetics of sulfur-oxidizing bacteria |journal=Adv Microb Physiol |volume=39 |issue= |pages=235–89 |year=1998 |pmid=9328649 |doi=10.1016/S0065-2911(08)60018-1 |series=Advances in Microbial Physiology |isbn=978-0-12-027739-1}}</ref> 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 [[nutrition|nutritious]] and which [[poison]]ous. For example, some [[prokaryote]]s 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.

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.

特定生物体的新陈代谢系统决定了哪些物质有营养，哪些有毒。例如，一些[[原核生物]]利用硫化氢作为营养物质，然而这种气体对动物是有毒的。生物体的[[基础代谢率]]是所有这些化学反应所消耗能量的量度。

特定生物体的新陈代谢系统决定了哪些物质有营养，哪些有毒。例如，一些[[原核生物]]利用硫化氢作为营养物质，然而这种气体对动物是有毒的<ref name="Physiology1">{{cite book |author=Friedrich C |title=Physiology and genetics of sulfur-oxidizing bacteria |journal=Adv Microb Physiol |volume=39 |issue= |pages=235–89 |year=1998 |pmid=9328649 |doi=10.1016/S0065-2911(08)60018-1 |series=Advances in Microbial Physiology |isbn=978-0-12-027739-1}}</ref>。生物体的[[基础代谢率]]是所有这些化学反应所消耗能量的量度。

更多信息：生物分子，细胞（生物学）和生物化学

更多信息：生物分子，细胞（生物学）和生物化学

[[File:Trimyristin-3D-vdW.png|right|thumb|upright=1.15|Structure of a [[triacylglycerol]] lipid]]

[[File:Trimyristin-3D-vdW.png|right|thumb|upright=1.15|[[三酰甘油脂]]的结构]]

[[File:Human Metabolism - Pathways.jpg|thumb|这张图表描绘了人体新陈代谢的一系列途径。]]

 

 

[[File:Human Metabolism - Pathways.jpg|thumb|This is a diagram depicting a large set of human metabolic pathways.]]

 

 

Most of the structures that make up animals, plants and microbes are made from four basic classes of [[molecule]]: [[amino acid]]s, [[carbohydrate]]s , [[nucleic acid]] and [[lipid]]s (often called [[fat]]s). 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 [[polymer]]s such as [[DNA]] and [[protein]]s, essential [[macromolecules]] of life.

Most of the structures that make up animals, plants and microbes are made from four basic classes of [[molecule]]: [[amino acid]]s, [[carbohydrate]]s , [[nucleic acid]] and [[lipid]]s (often called [[fat]]s). 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 [[polymer]]s such as [[DNA]] and [[protein]]s, essential [[macromolecules]] of life.

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.

[[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<ref>{{cite journal|last1=Berg|first1=Jeremy M.|last2=Tymoczko|first2=John L.|last3=Stryer|first3=Lubert | name-list-style = vanc |date=2002|title=Vitamins Are Often Precursors to Coenzymes|url=https://www.ncbi.nlm.nih.gov/books/NBK22549/|journal=Biochemistry. 5th Edition|language=en}}</ref>。[[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<ref>{{cite journal | vauthors = Pollak N, Dölle C, Ziegler M | title = The power to reduce: pyridine nucleotides--small molecules with a multitude of functions | journal = The Biochemical Journal | volume = 402 | issue = 2 | pages = 205–18 | date = March 2007 | pmid = 17295611 | pmc = 1798440 | doi = 10.1042/BJ20061638 }}</ref>，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<ref>{{cite book|last=Fatih|first=Yildiz | name-list-style = vanc |title=Advances in food biochemistry|publisher=CRC Press|year=2009|isbn=978-1-4200-0769-5|location=Boca Raton|pages=228|oclc=607553259}}</ref>。

[[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<ref>{{cite journal|last1=Berg|first1=Jeremy M.|last2=Tymoczko|first2=John L.|last3=Stryer|first3=Lubert | name-list-style = vanc |date=2002|title=Vitamins Are Often Precursors to Coenzymes|url=https://www.ncbi.nlm.nih.gov/books/NBK22549/|journal=Biochemistry. 5th Edition|language=en}}</ref>。[[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⁺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<ref>{{cite journal | vauthors = Pollak N, Dölle C, Ziegler M | title = The power to reduce: pyridine nucleotides--small molecules with a multitude of functions | journal = The Biochemical Journal | volume = 402 | issue = 2 | pages = 205–18 | date = March 2007 | pmid = 17295611 | pmc = 1798440 | doi = 10.1042/BJ20061638 }}</ref>，即NADH和NADPH。NAD ⁺/NADH 形式在分解代谢反应中起重要作用，而 NADP ⁺/NADPH 形式在分解代谢反应中起重要作用<ref>{{cite book|last=Fatih|first=Yildiz | name-list-style = vanc |title=Advances in food biochemistry|publisher=CRC Press|year=2009|isbn=978-1-4200-0769-5|location=Boca Raton|pages=228|oclc=607553259}}</ref>。

微生物简单直接地将消化酶分泌到周围环境中<ref>{{cite journal | vauthors = Häse CC, Finkelstein RA | title = Bacterial extracellular zinc-containing metalloproteases | journal = Microbiological Reviews | volume = 57 | issue = 4 | pages = 823–37 | date = December 1993 | pmid = 8302217 | pmc = 372940 | doi = 10.1128/MMBR.57.4.823-837.1993 }}</ref><ref>{{cite journal | vauthors = Gupta R, Gupta N, Rathi P | title = Bacterial lipases: an overview of production, purification and biochemical properties | journal = Applied Microbiology and Biotechnology | volume = 64 | issue = 6 | pages = 763–81 | date = June 2004 | pmid = 14966663 | doi = 10.1007/s00253-004-1568-8 | s2cid = 206934353 }}</ref>，而动物必须通过它们肠道(包括胃、胰腺和唾液腺)中的特定细胞分泌这些酶。<ref>{{cite journal | vauthors = Hoyle T | title = The digestive system: linking theory and practice | journal = British Journal of Nursing | volume = 6 | issue = 22 | pages = 1285–91 | year = 1997 | pmid = 9470654 | doi = 10.12968/bjon.1997.6.22.1285 }}</ref>这些细胞外酶释放的氨基酸或糖通过活性转运蛋白被泵入细胞内<ref>{{cite journal | vauthors = Souba WW, Pacitti AJ | title = How amino acids get into cells: mechanisms, models, menus, and mediators | journal = JPEN. Journal of Parenteral and Enteral Nutrition | volume = 16 | issue = 6 | pages = 569–78 | year = 1992 | pmid = 1494216 | doi = 10.1177/0148607192016006569 }}</ref><ref>{{cite journal | vauthors = Barrett MP, Walmsley AR, Gould GW | title = Structure and function of facilitative sugar transporters | journal = Current Opinion in Cell Biology | volume = 11 | issue = 4 | pages = 496–502 | date = August 1999 | pmid = 10449337 | doi = 10.1016/S0955-0674(99)80072-6 }}</ref>。

微生物简单直接地将消化酶分泌到周围环境中<ref>{{cite journal | vauthors = Häse CC, Finkelstein RA | title = Bacterial extracellular zinc-containing metalloproteases | journal = Microbiological Reviews | volume = 57 | issue = 4 | pages = 823–37 | date = December 1993 | pmid = 8302217 | pmc = 372940 | doi = 10.1128/MMBR.57.4.823-837.1993 }}</ref><ref>{{cite journal | vauthors = Gupta R, Gupta N, Rathi P | title = Bacterial lipases: an overview of production, purification and biochemical properties | journal = Applied Microbiology and Biotechnology | volume = 64 | issue = 6 | pages = 763–81 | date = June 2004 | pmid = 14966663 | doi = 10.1007/s00253-004-1568-8 | s2cid = 206934353 }}</ref>，而动物必须通过它们肠道(包括胃、胰腺和唾液腺)中的特定细胞分泌这些酶。<ref>{{cite journal | vauthors = Hoyle T | title = The digestive system: linking theory and practice | journal = British Journal of Nursing | volume = 6 | issue = 22 | pages = 1285–91 | year = 1997 | pmid = 9470654 | doi = 10.12968/bjon.1997.6.22.1285 }}</ref>这些细胞外酶释放的氨基酸或糖通过活性转运蛋白被泵入细胞内<ref>{{cite journal | vauthors = Souba WW, Pacitti AJ | title = How amino acids get into cells: mechanisms, models, menus, and mediators | journal = JPEN. Journal of Parenteral and Enteral Nutrition | volume = 16 | issue = 6 | pages = 569–78 | year = 1992 | pmid = 1494216 | doi = 10.1177/0148607192016006569 }}</ref><ref>{{cite journal | vauthors = Barrett MP, Walmsley AR, Gould GW | title = Structure and function of facilitative sugar transporters | journal = Current Opinion in Cell Biology | volume = 11 | issue = 4 | pages = 496–502 | date = August 1999 | pmid = 10449337 | doi = 10.1016/S0955-0674(99)80072-6 }}</ref>。

[[File:Catabolism schematic.svg|thumb|left|upright=1.35|A simplified outline of the catabolism of [[protein]]s, [[carbohydrate]]s and [[fat]]s]]

[[File:Catabolism schematic.svg|thumb|left|upright=1.35|[[蛋白质]]，[[碳水化合物]]和[[脂肪]]分解代谢的简化概述 ]]

氧化磷酸化中，通过如柠檬酸循环等代谢途径，电子从被消化吸收的食物分子上转移到氧气上，并将产生的能量以ATP的方式储存起来。在真核生物中，这一过程是通过线粒体膜上的一系列膜蛋白来完成的，被称为电子传递链。而在原核生物中，这些蛋白质存在于细胞的内膜中。<ref>{{cite journal | vauthors = Hosler JP, Ferguson-Miller S, Mills DA | title = Energy transduction: proton transfer through the respiratory complexes | journal = Annual Review of Biochemistry | volume = 75 | issue =  | pages = 165–87 | year = 2006 | pmid = 16756489 | pmc = 2659341 | doi = 10.1146/annurev.biochem.75.062003.101730 }}</ref>这些蛋白质利用电子从还原性分子(如NADH)传递到氧气所释放的能量来泵送质子穿过细胞膜<ref>{{cite journal | vauthors = Schultz BE, Chan SI | title = Structures and proton-pumping strategies of mitochondrial respiratory enzymes | journal = Annual Review of Biophysics and Biomolecular Structure | volume = 30 | issue =  | pages = 23–65 | year = 2001 | pmid = 11340051 | doi = 10.1146/annurev.biophys.30.1.23 | url = https://authors.library.caltech.edu/1623/1/SCHarbbs01.pdf }}</ref>。

氧化磷酸化中，通过如柠檬酸循环等代谢途径，电子从被消化吸收的食物分子上转移到氧气上，并将产生的能量以ATP的方式储存起来。在真核生物中，这一过程是通过线粒体膜上的一系列膜蛋白来完成的，被称为电子传递链。而在原核生物中，这些蛋白质存在于细胞的内膜中。<ref>{{cite journal | vauthors = Hosler JP, Ferguson-Miller S, Mills DA | title = Energy transduction: proton transfer through the respiratory complexes | journal = Annual Review of Biochemistry | volume = 75 | issue =  | pages = 165–87 | year = 2006 | pmid = 16756489 | pmc = 2659341 | doi = 10.1146/annurev.biochem.75.062003.101730 }}</ref>这些蛋白质利用电子从还原性分子(如NADH)传递到氧气所释放的能量来泵送质子穿过细胞膜<ref>{{cite journal | vauthors = Schultz BE, Chan SI | title = Structures and proton-pumping strategies of mitochondrial respiratory enzymes | journal = Annual Review of Biophysics and Biomolecular Structure | volume = 30 | issue =  | pages = 23–65 | year = 2001 | pmid = 11340051 | doi = 10.1146/annurev.biophys.30.1.23 | url = https://authors.library.caltech.edu/1623/1/SCHarbbs01.pdf }}</ref>。

[[File:ATPsyn.gif|thumb|right|Mechanism of [[ATP synthase]]. ATP is shown in red, ADP and phosphate in pink and the rotating stalk subunit in black.]]

[[File:ATPsyn.gif|thumb|right|[[ATP合成酶]]的作用机制。ATP 显示为红色，ADP 和磷酸显示为粉红色，转柄亚基显示为黑色]]

 

Mechanism of [[ATP synthase. ATP is shown in red, ADP and phosphate in pink and the rotating stalk subunit in black.]]

Pumping protons out of the mitochondria creates a proton [[diffusion|concentration difference]] across the membrane and generates an [[electrochemical gradient]]. This force drives protons back into the mitochondrion through the base of an enzyme called [[ATP synthase]]. The flow of protons makes the stalk subunit rotate, causing the [[active site]] of the synthase domain to change shape and phosphorylate [[adenosine diphosphate]]&nbsp;– turning it into ATP.

Pumping protons out of the mitochondria creates a proton [[diffusion|concentration difference]] across the membrane and generates an [[electrochemical gradient]]. This force drives protons back into the mitochondrion through the base of an enzyme called [[ATP synthase]]. The flow of protons makes the stalk subunit rotate, causing the [[active site]] of the synthase domain to change shape and phosphorylate [[adenosine diphosphate]]&nbsp;– turning it into ATP.

更多信息：光合作用，碳固定和化学合成

更多信息：光合作用，碳固定和化学合成

[[File:Plagiomnium affine laminazellen.jpeg|thumb|Plant cells (bounded by purple walls) filled with chloroplasts (green), which are the site of photosynthesis]]

[[File:Plagiomnium affine laminazellen.jpeg|thumb|含叶绿体（绿色）的植物细胞（以紫色壁为边界），叶绿体是光合作用的部位]]

 

Photosynthesis is the synthesis of carbohydrates from sunlight and [[carbon dioxide]] (CO₂). In plants, cyanobacteria and algae, oxygenic photosynthesis splits water, with oxygen produced as a waste product. This process uses the ATP and NADPH produced by the [[photosynthetic reaction centre]]s, as described above, to convert CO₂ into [[glycerate 3-phosphate]], which can then be converted into glucose. This carbon-fixation reaction is carried out by the enzyme [[RuBisCO]] as part of the [[Calvin cycle|Calvin&nbsp;– Benson cycle]]. Three types of photosynthesis occur in plants, [[C3 carbon fixation]], [[C4 carbon fixation]] and [[Crassulacean acid metabolism|CAM photosynthesis]]. These differ by the route that carbon dioxide takes to the Calvin cycle, with C3 plants fixing CO₂ directly, while C4 and CAM photosynthesis incorporate the CO₂ into other compounds first, as adaptations to deal with intense sunlight and dry conditions.

Photosynthesis is the synthesis of carbohydrates from sunlight and [[carbon dioxide]] (CO₂). In plants, cyanobacteria and algae, oxygenic photosynthesis splits water, with oxygen produced as a waste product. This process uses the ATP and NADPH produced by the [[photosynthetic reaction centre]]s, as described above, to convert CO₂ into [[glycerate 3-phosphate]], which can then be converted into glucose. This carbon-fixation reaction is carried out by the enzyme [[RuBisCO]] as part of the [[Calvin cycle|Calvin&nbsp;– Benson cycle]]. Three types of photosynthesis occur in plants, [[C3 carbon fixation]], [[C4 carbon fixation]] and [[Crassulacean acid metabolism|CAM photosynthesis]]. These differ by the route that carbon dioxide takes to the Calvin cycle, with C3 plants fixing CO₂ directly, while C4 and CAM photosynthesis incorporate the CO₂ into other compounds first, as adaptations to deal with intense sunlight and dry conditions.

更多信息：脂肪酸合成和类固醇代谢

更多信息：脂肪酸合成和类固醇代谢

[[File:Sterol synthesis.svg|thumb|right|upright=1.6|Simplified version of the [[steroid synthesis]] pathway with the intermediates [[isopentenyl pyrophosphate]] (IPP), [[dimethylallyl pyrophosphate]] (DMAPP), [[geranyl pyrophosphate]] (GPP) and [[squalene]] shown. Some intermediates are omitted for clarity.]]

[[File:Sterol synthesis.svg|thumb|right|upright=1.6|具有中间体[[异戊烯基焦磷酸酯]]（IPP），[[二甲基烯丙基焦磷酸酯]]（DMAPP），[[香叶基焦磷酸酯]]（GPP）和[[角鲨烯的类固醇]]合成途径的简化版本。为了清晰起见，省略了一些中间步骤。]]

 

Simplified version of the [[steroid synthesis pathway with the intermediates isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted for clarity.]]

 

Fatty acids are made by [[fatty acid synthase]]s that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acyl group, reduce it to an alcohol, [[dehydration reaction|dehydrate]] it to an [[alkene]] group and then reduce it again to an [[alkane]] group. The enzymes of fatty acid biosynthesis are divided into two groups: in animals and fungi, all these fatty acid synthase reactions are carried out by a single multifunctional type I protein, while in plant [[plastid]]s and bacteria separate type II enzymes perform each step in the pathway.

Fatty acids are made by [[fatty acid synthase]]s that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acyl group, reduce it to an alcohol, [[dehydration reaction|dehydrate]] it to an [[alkene]] group and then reduce it again to an [[alkane]] group. The enzymes of fatty acid biosynthesis are divided into two groups: in animals and fungi, all these fatty acid synthase reactions are carried out by a single multifunctional type I protein, while in plant [[plastid]]s and bacteria separate type II enzymes perform each step in the pathway.

由于大多数生物体的环境是不断变化的，因此它们必须对新陈代谢的反应进行精细的调节，以维持细胞内一系列恒定的条件，这种条件称为稳态<ref>{{cite journal | vauthors = Albert R | title = Scale-free networks in cell biology | journal = Journal of Cell Science | volume = 118 | issue = Pt 21 | pages = 4947–57 | date = November 2005 | pmid = 16254242 | doi = 10.1242/jcs.02714 | arxiv = q-bio/0510054 | s2cid = 3001195 | bibcode = 2005q.bio....10054A }}</ref><ref>{{cite journal | vauthors = Brand MD | title = Regulation analysis of energy metabolism | journal = The Journal of Experimental Biology | volume = 200 | issue = Pt 2 | pages = 193–202 | date = January 1997 | pmid = 9050227 | url = http://jeb.biologists.org/cgi/reprint/200/2/193 }}</ref>。代谢调节也使生物体能够对信号作出反应，并与环境积极互动。有两个密切相关的概念对于理解“代谢途径是如何被控制的”十分重要<ref>{{cite journal | vauthors = Soyer OS, Salathé M, Bonhoeffer S | title = Signal transduction networks: topology, response and biochemical processes | journal = Journal of Theoretical Biology | volume = 238 | issue = 2 | pages = 416–25 | date = January 2006 | pmid = 16045939 | doi = 10.1016/j.jtbi.2005.05.030 }}</ref>。首先，途径中酶的调节是指其活性如何响应信号从而增加和减少。其次，这种酶所施加的控制是指它的活性变化对通路的总体速率（通过通路的通量）的影响<ref name=Salter>{{cite journal | vauthors = Salter M, Knowles RG, Pogson CI | title = Metabolic control | journal = Essays in Biochemistry | volume = 28 | issue =  | pages = 1–12 | year = 1994 | pmid = 7925313 }}</ref>。例如，一种酶可能表现出很大的活性变化(即它是高度受控的)，但如果这些变化对某一代谢途径的通量影响不大，那么这种酶就不参与该途径的控制<ref>{{cite journal | vauthors = Westerhoff HV, Groen AK, Wanders RJ | title = Modern theories of metabolic control and their applications (review) | journal = Bioscience Reports | volume = 4 | issue = 1 | pages = 1–22 | date = January 1984 | pmid = 6365197 | doi = 10.1007/BF01120819 | s2cid = 27791605 }}</ref>。

由于大多数生物体的环境是不断变化的，因此它们必须对新陈代谢的反应进行精细的调节，以维持细胞内一系列恒定的条件，这种条件称为稳态<ref>{{cite journal | vauthors = Albert R | title = Scale-free networks in cell biology | journal = Journal of Cell Science | volume = 118 | issue = Pt 21 | pages = 4947–57 | date = November 2005 | pmid = 16254242 | doi = 10.1242/jcs.02714 | arxiv = q-bio/0510054 | s2cid = 3001195 | bibcode = 2005q.bio....10054A }}</ref><ref>{{cite journal | vauthors = Brand MD | title = Regulation analysis of energy metabolism | journal = The Journal of Experimental Biology | volume = 200 | issue = Pt 2 | pages = 193–202 | date = January 1997 | pmid = 9050227 | url = http://jeb.biologists.org/cgi/reprint/200/2/193 }}</ref>。代谢调节也使生物体能够对信号作出反应，并与环境积极互动。有两个密切相关的概念对于理解“代谢途径是如何被控制的”十分重要<ref>{{cite journal | vauthors = Soyer OS, Salathé M, Bonhoeffer S | title = Signal transduction networks: topology, response and biochemical processes | journal = Journal of Theoretical Biology | volume = 238 | issue = 2 | pages = 416–25 | date = January 2006 | pmid = 16045939 | doi = 10.1016/j.jtbi.2005.05.030 }}</ref>。首先，途径中酶的调节是指其活性如何响应信号从而增加和减少。其次，这种酶所施加的控制是指它的活性变化对通路的总体速率（通过通路的通量）的影响<ref name=Salter>{{cite journal | vauthors = Salter M, Knowles RG, Pogson CI | title = Metabolic control | journal = Essays in Biochemistry | volume = 28 | issue =  | pages = 1–12 | year = 1994 | pmid = 7925313 }}</ref>。例如，一种酶可能表现出很大的活性变化(即它是高度受控的)，但如果这些变化对某一代谢途径的通量影响不大，那么这种酶就不参与该途径的控制<ref>{{cite journal | vauthors = Westerhoff HV, Groen AK, Wanders RJ | title = Modern theories of metabolic control and their applications (review) | journal = Bioscience Reports | volume = 4 | issue = 1 | pages = 1–22 | date = January 1984 | pmid = 6365197 | doi = 10.1007/BF01120819 | s2cid = 27791605 }}</ref>。

[[File:Insulin glucose metabolism ZP.svg|thumb|right|upright=1.35|'''Effect of insulin on glucose uptake and metabolism.''' Insulin binds to its receptor (1), which in turn starts many protein activation cascades (2). These include: translocation of Glut-4 transporter to the [[plasma membrane]] and influx of glucose (3), [[glycogen]] synthesis (4), [[glycolysis]] (5) and [[fatty acid]] synthesis (6).]]

[[File:Insulin glucose metabolism ZP.svg|thumb|right|upright=1.35|胰岛素对葡萄糖摄取和代谢的影响。胰岛素与其受体（1）结合，继而启动许多蛋白质激活级联反应（2）。其中包括：Glut-4转运蛋白向[[质膜]]的转运和葡萄糖的流入（3），[[糖原]]合成（4），[[糖酵解]]（5）和[[脂肪酸]]合成（6）。]]

 

Effect of insulin on glucose uptake and metabolism. Insulin binds to its receptor (1), which in turn starts many protein activation cascades (2). These include: translocation of Glut-4 transporter to the [[plasma membrane and influx of glucose (3), glycogen synthesis (4), glycolysis (5) and fatty acid synthesis (6).]]

 

There are multiple levels of metabolic regulation. In intrinsic regulation, the metabolic pathway self-regulates to respond to changes in the levels of substrates or products; for example, a decrease in the amount of product can increase the [[flux]] through the pathway to compensate. This type of regulation often involves [[allosteric regulation]] of the activities of multiple enzymes in the pathway. Extrinsic control involves a cell in a multicellular organism changing its metabolism in response to signals from other cells. These signals are usually in the form of water soluble messengers such as [[hormone]]s and [[growth factor]]s and are detected by specific [[receptor (biochemistry)|receptors]] on the cell surface. These signals are then transmitted inside the cell by [[second messenger system]]s that often involved the [[phosphorylation]] of proteins.

There are multiple levels of metabolic regulation. In intrinsic regulation, the metabolic pathway self-regulates to respond to changes in the levels of substrates or products; for example, a decrease in the amount of product can increase the [[flux]] through the pathway to compensate. This type of regulation often involves [[allosteric regulation]] of the activities of multiple enzymes in the pathway. Extrinsic control involves a cell in a multicellular organism changing its metabolism in response to signals from other cells. These signals are usually in the form of water soluble messengers such as [[hormone]]s and [[growth factor]]s and are detected by specific [[receptor (biochemistry)|receptors]] on the cell surface. These signals are then transmitted inside the cell by [[second messenger system]]s that often involved the [[phosphorylation]] of proteins.

更多信息：分子进化与系统发育

更多信息：分子进化与系统发育

[[File:Tree of life int.svg|thumb|right|upright=1.8|[[Phylogenetic tree|Evolutionary tree]] showing the common ancestry of organisms from all three [[Domain (biology)|domains]] of life. [[Bacteria]] are colored blue, [[eukaryote]]s red, and [[archaea]] green. Relative positions of some of the [[phylum|phyla]] included are shown around the tree.]]

[[File:Tree of life int.svg|thumb|right|upright=1.8|[[演化树显示了来自全部三个生命领域的生物体的共同祖先。[[细菌]]呈蓝色，[[真核生物]]呈红色，[[古菌]]呈绿色。树木周围显示了一些门的相对位置。]]

Evolutionary tree showing the common ancestry of organisms from all three domains of life. Bacteria are colored blue, eukaryotes red, and archaea green. Relative positions of some of the phyla included are shown around the tree.]]

Evolutionary tree showing the common ancestry of organisms from all three domains of life. Bacteria are colored blue, eukaryotes red, and archaea green. Relative positions of some of the phyla included are shown around the tree.]]

The central pathways of metabolism described above, such as glycolysis and the citric acid cycle, are present in all [[Three-domain system|three domains]] of living things and were present in the [[last universal common ancestor]]. This universal ancestral cell was [[prokaryote|prokaryotic]] and probably a [[methanogen]] that had extensive amino acid, nucleotide, carbohydrate and lipid metabolism. The retention of these ancient pathways during later [[evolution]] may be the result of these reactions having been an optimal solution to their particular metabolic problems, with pathways such as glycolysis and the citric acid cycle producing their end products highly efficiently and in a minimal number of steps. The first pathways of enzyme-based metabolism may have been parts of [[purine]] nucleotide metabolism, while previous metabolic pathways were a part of the ancient [[RNA world hypothesis|RNA world]].

The central pathways of metabolism described above, such as glycolysis and the citric acid cycle, are present in all [[Three-domain system|three domains]] of living things and were present in the [[last universal common ancestor]]. This universal ancestral cell was [[prokaryote|prokaryotic]] and probably a [[methanogen]] that had extensive amino acid, nucleotide, carbohydrate and lipid metabolism. The retention of these ancient pathways during later [[evolution]] may be the result of these reactions having been an optimal solution to their particular metabolic problems, with pathways such as glycolysis and the citric acid cycle producing their end products highly efficiently and in a minimal number of steps. The first pathways of enzyme-based metabolism may have been parts of [[purine]] nucleotide metabolism, while previous metabolic pathways were a part of the ancient [[RNA world hypothesis|RNA world]].

更多信息：蛋白质方法，蛋白质组学，代谢组学和代谢网络建模

更多信息：蛋白质方法，蛋白质组学，代谢组学和代谢网络建模

[[File:A thaliana metabolic network.png|thumb|upright=1.35|right|[[Metabolic network]] of the ''[[Arabidopsis thaliana]]'' [[citric acid cycle]]. [[Enzyme]]s and [[metabolite]]s are shown as red squares and the interactions between them as black lines.]]

[[File:A thaliana metabolic network.png|thumb|upright=1.35|right|[[拟南芥]][[三羧酸循环]]的[[代谢网络]]。[[酶]]和[[代谢物]]显示为红色方块，它们之间的相互作用显示为黑线。]]

 

 

[拟南芥三羧酸循环的代谢网络。酶和代谢物显示为红色方块，它们之间的相互作用显示为黑线。]

Classically, metabolism is studied by a [[reductionism|reductionist]] approach that focuses on a single metabolic pathway. Particularly valuable is the use of [[radioactive tracer]]s at the whole-organism, tissue and cellular levels, which define the paths from precursors to final products by identifying radioactively labelled intermediates and products. The enzymes that catalyze these chemical reactions can then be [[protein purification|purified]] and their [[enzyme kinetics|kinetics]] and responses to [[enzyme inhibitor|inhibitors]] investigated. A parallel approach is to identify the small molecules in a cell or tissue; the complete set of these molecules is called the [[metabolome]]. Overall, these studies give a good view of the structure and function of simple metabolic pathways, but are inadequate when applied to more complex systems such as the metabolism of a complete cell.

Classically, metabolism is studied by a [[reductionism|reductionist]] approach that focuses on a single metabolic pathway. Particularly valuable is the use of [[radioactive tracer]]s at the whole-organism, tissue and cellular levels, which define the paths from precursors to final products by identifying radioactively labelled intermediates and products. The enzymes that catalyze these chemical reactions can then be [[protein purification|purified]] and their [[enzyme kinetics|kinetics]] and responses to [[enzyme inhibitor|inhibitors]] investigated. A parallel approach is to identify the small molecules in a cell or tissue; the complete set of these molecules is called the [[metabolome]]. Overall, these studies give a good view of the structure and function of simple metabolic pathways, but are inadequate when applied to more complex systems such as the metabolism of a complete cell.

新陈代谢这一术语源于法语“ métabolisme”或古希腊语 μταβoλλ -“Metabole”意为某种改变，它源自意为“去改变”的“ Metaballein”<ref>{{Cite web|title=metabolism {{!}} Origin and meaning of metabolism by Online Etymology Dictionary|url=https://www.etymonline.com/word/metabolism|access-date=2020-07-23|website=www.etymonline.com|language=en}}</ref>

新陈代谢这一术语源于法语“ métabolisme”或古希腊语 μταβoλλ -“Metabole”意为某种改变，它源自意为“去改变”的“ Metaballein”<ref>{{Cite web|title=metabolism {{!}} Origin and meaning of metabolism by Online Etymology Dictionary|url=https://www.etymonline.com/word/metabolism|access-date=2020-07-23|website=www.etymonline.com|language=en}}</ref>

[[File:Aristotle's metabolism.png|thumb|right|upright=1.4|[[Aristotle's biology|Aristotle's metabolism]] as an open flow model]]

[[File:Aristotle's metabolism.png|thumb|right|upright=1.4|亚里士多德Aristotle的新陈代谢是一个开放性的流动模型。]]

 

Aristotle's metabolism as an open flow model]]

===Greek philosophy===

===Greek philosophy===

新陈代谢的科学研究历史跨越了几个世纪，从早期研究中对动物整体的研究，到现代生物化学中对单个代谢反应的研究。 人类新陈代谢的第一个对照实验是由圣托里奥·桑托里奥 Santorio Santorio于1614年在他的著作《静态医学》中发表的<ref>{{cite journal | vauthors = Eknoyan G | title = Santorio Sanctorius (1561-1636) - founding father of metabolic balance studies | journal = American Journal of Nephrology | volume = 19 | issue = 2 | pages = 226–33 | year = 1999 | pmid = 10213823 | doi = 10.1159/000013455 | s2cid = 32900603 }}</ref>。他描述了自己在进食、睡觉、工作、性交、禁食、饮水和排泄前后的体重。他发现他摄入的大部分食物都是通过他所谓的“无知觉的汗液”流失的。

新陈代谢的科学研究历史跨越了几个世纪，从早期研究中对动物整体的研究，到现代生物化学中对单个代谢反应的研究。 人类新陈代谢的第一个对照实验是由圣托里奥·桑托里奥 Santorio Santorio于1614年在他的著作《静态医学》中发表的<ref>{{cite journal | vauthors = Eknoyan G | title = Santorio Sanctorius (1561-1636) - founding father of metabolic balance studies | journal = American Journal of Nephrology | volume = 19 | issue = 2 | pages = 226–33 | year = 1999 | pmid = 10213823 | doi = 10.1159/000013455 | s2cid = 32900603 }}</ref>。他描述了自己在进食、睡觉、工作、性交、禁食、饮水和排泄前后的体重。他发现他摄入的大部分食物都是通过他所谓的“无知觉的汗液”流失的。

[[File:SantoriosMeal.jpg|thumb|right|upright=0.7|[[Santorio Santorio]] in his steelyard balance, from ''Ars de statica medicina'', first published 1614]]

[[File:SantoriosMeal.jpg|thumb|right|upright=0.7|Santorio Santorio 在他的杆秤上，来自静态医学，1614年首次发表]]

 

 

In these early studies, the mechanisms of these metabolic processes had not been identified and a [[vitalism|vital force]] was thought to animate living tissue. In the 19th century, when studying the [[fermentation (food)|fermentation]] of sugar to [[ethanol|alcohol]] by [[yeast]], [[Louis Pasteur]] concluded that fermentation was catalyzed by substances within the yeast cells he called "ferments". He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells." This discovery, along with the publication by [[Friedrich Woehler|Friedrich Wöhler]] in 1828 of a paper on the chemical synthesis of [[urea]], and is notable for being the first organic compound prepared from wholly inorganic precursors. This proved that the organic compounds and chemical reactions found in cells were no different in principle than any other part of chemistry.

In these early studies, the mechanisms of these metabolic processes had not been identified and a [[vitalism|vital force]] was thought to animate living tissue. In the 19th century, when studying the [[fermentation (food)|fermentation]] of sugar to [[ethanol|alcohol]] by [[yeast]], [[Louis Pasteur]] concluded that fermentation was catalyzed by substances within the yeast cells he called "ferments". He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells." This discovery, along with the publication by [[Friedrich Woehler|Friedrich Wöhler]] in 1828 of a paper on the chemical synthesis of [[urea]], and is notable for being the first organic compound prepared from wholly inorganic precursors. This proved that the organic compounds and chemical reactions found in cells were no different in principle than any other part of chemistry.