{{Short description|Study of chemical processes of living organisms}}
{{redir2|Biological chemistry|Physiological chemistry|the journals|Biochemistry (journal){{!}}''Biochemistry'' (journal)|and|Biological Chemistry (journal){{!}}''Biological Chemistry'' (journal)}}
{{for|the textbook by Lubert Stryer|Biochemistry (book){{!}}''Biochemistry'' (book)}}
{{Biochemistry sidebar}}
{{refimprove|date=August 2025}}
'''Biochemistry''', or '''biological chemistry''' (distinct from [[chemical biology]]), is the study of [[chemical process]]es within and relating to living [[organism]]s.<ref>{{cite web|url=http://www.acs.org/content/acs/en/careers/college-to-career/areas-of-chemistry/biological-biochemistry.html.html|title=Biological/Biochemistry|work=acs.org|access-date=2016-01-04|archive-date=2019-08-21|archive-url=https://web.archive.org/web/20190821192332/https://www.acs.org/content/acs/en/careers/college-to-career/areas-of-chemistry/biological-biochemistry.html.html|url-status=live}}</ref>  A sub-discipline of both [[chemistry]] and [[biology]], biochemistry may be divided into three fields: [[structural biology]], [[enzymology]], and [[metabolism]]. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines.  Almost all [[List of life sciences|areas of the life sciences]] are being uncovered and developed through biochemical methodology and research.<ref name="Voet_2005">[[#Voet|Voet]] (2005), p. 3.</ref>  

Biochemistry focuses on understanding the chemical basis that allows [[biomolecule|biological molecules]] to give rise to the processes that occur within living [[Cell (biology)|cells]] and between cells,<ref name="Karp2009">[[#Karp|Karp]] (2009), p. 2.</ref> in turn relating greatly to the understanding of [[tissue (biology)|tissues]] and [[organ (anatomy)|organs]] as well as organism structure and function.<ref name="MillerSpoolman2012">[[#Miller|Miller]] (2012). p. 62.</ref> Biochemistry is closely related to [[molecular biology]], the study of the [[molecule|molecular]] mechanisms of biological phenomena.<ref name="fn_1">[[#Astbury|Astbury]] (1961), p. 1124.</ref>

Much of biochemistry deals with the structures, functions, and interactions of biological [[macromolecule]]s such as [[protein]]s, [[nucleic acid]]s, [[carbohydrate]]s, and [[lipid]]s. They provide the structure of cells and perform many of the functions associated with life.<ref name="Biology">[[#Eldra|Eldra]] (2007), p. 45.</ref> The [[chemistry]] of the cell also depends upon the reactions of small [[molecule]]s and [[ion]]s.  These can be [[inorganic]] (for example, [[water]] and [[metal]] ions) or [[Organic compound|organic]] (for example, the [[amino acid]]s, which are used to [[Protein biosynthesis|synthesize proteins]]).<ref name="Marks">[[#Marks|Marks]] (2012), Chapter 14.</ref> The mechanisms used by [[Cell energy|cells to harness energy]] from their environment via [[chemical reaction]]s are known as [[metabolism]].

The findings of biochemistry are applied primarily in [[medicine]], [[nutrition]], and [[agriculture]]. In medicine, [[biochemist]]s investigate the causes and [[Pharmaceutical drug|cures]] of [[disease]]s.<ref>[[#Finkel|Finkel]] (2009), pp. 1–4.</ref> Nutrition studies how to maintain health and wellness and also the effects of [[nutritional deficiencies]].<ref name="FFL2010">[[#UNICEF|UNICEF]] (2010), pp. 61, 75.</ref> In agriculture, biochemists investigate [[soil]] and [[fertilizer]]s with the goal of improving crop cultivation, crop storage, and [[pest control]]. In recent decades, biochemical principles and methods have been combined with problem-solving approaches from [[engineering]] to manipulate living systems in order to produce useful tools for research, industrial processes, and diagnosis and control of disease{{mdash}}the discipline of [[biotechnology]].

==History==
{{Main| History of biochemistry}}
[[File:Gerty Theresa Radnitz Cori (1896-1957) and Carl Ferdinand Cori - restoration1.jpg|thumb|upright|[[Gerty Cori]] and [[Carl Cori]] jointly won the [[Nobel Prize in Physiology or Medicine|Nobel Prize]] in 1947 for their discovery of the [[Cori cycle]] at RPMI.]]

At its most comprehensive definition, biochemistry can be seen as a study of the components and composition of living things and how they come together to become life. In this sense, the history of biochemistry may therefore go back as far as the [[Ancient Greece|ancient Greeks]].<ref name="history of science">[[#Helvoort|Helvoort]] (2000), p. 81.</ref> However, biochemistry as a specific [[scientific discipline]] began sometime in the 19th century, or a little earlier, depending on which aspect of biochemistry is being focused on. Some argued that the beginning of biochemistry may have been the discovery of the first [[enzyme]], [[diastase]] (now called [[amylase]]), in 1833 by [[Anselme Payen]],<ref>[[#Hunter|Hunter]] (2000), p. 75.</ref> while others considered [[Eduard Buchner]]'s first demonstration of a complex biochemical process [[Ethanol fermentation|alcoholic fermentation]] in cell-free extracts in 1897 to be the birth of biochemistry.<ref>[[#Hamblin|Hamblin]] (2005), p. 26.</ref><ref>[[#Hunter|Hunter]] (2000), pp. 96–98.</ref>  Some might also point as its beginning to the influential 1842 work by [[Justus von Liebig]], ''Animal chemistry, or, [[Organic chemistry]] in its applications to [[physiology]] and [[pathology]]'', which presented a chemical theory of metabolism,<ref name="history of science" /> or even earlier to the 18th century studies on [[fermentation]] and [[Cellular respiration|respiration]] by [[Antoine Lavoisier]].<ref>[[#Berg|Berg]] (1980), pp. 1–2.</ref><ref>[[#Holmes|Holmes]] (1987), p. xv.</ref> Many other pioneers in the field who helped to uncover the layers of complexity of biochemistry have been proclaimed founders of modern biochemistry. [[Hermann Emil Fischer|Emil Fischer]], who studied the chemistry of [[proteins]],<ref>[[#Feldman|Feldman]] (2001), p. 206.</ref> and [[Frederick Gowland Hopkins|F. Gowland Hopkins]], who studied [[enzymes]] and the dynamic nature of biochemistry, represent two examples of early biochemists.<ref>[[#Rayner|Rayner-Canham]] (2005), p. 136.</ref>

The term "biochemistry" was first used when Vinzenz Kletzinsky (1826–1882) had his "Compendium der Biochemie" printed in Vienna in 1858; it derived from a combination of [[biology]] and [[chemistry]]. In 1877, [[Felix Hoppe-Seyler]] used the term ({{Lang|de|biochemie}} in German) as a synonym for [[physiological chemistry]] in the foreword to the first issue of ''[[Zeitschrift für Physiologische Chemie]]'' (Journal of Physiological Chemistry) where he argued for the setting up of institutes dedicated to this field of study.<ref>[[#Ziesak|Ziesak]] (1999), p. 169.</ref><ref>[[#Kleinkauf|Kleinkauf]] (1988), p. 116.</ref> The German [[chemist]] [[Carl Neuberg]] however is often cited to have coined the word in 1903,<ref name="Ben-Menahem 2009">[[#Ben|Ben-Menahem]] (2009), p. 2982.</ref><ref>[[#Amsler|Amsler]] (1986), p. 55.</ref><ref>[[#Horton|Horton]] (2013), p. 36.</ref> while some credited it to [[Franz Hofmeister]].<ref>[[#Kleinkauf|Kleinkauf]] (1988), p. 43.</ref>

[[File:DNA orbit animated.gif|thumb|left|upright|DNA structure ({{PDB2|1D65}})<ref>[[#Edwards|Edwards]] (1992), pp. 1161–1173.</ref>]]
It was once generally believed that life and its materials had some essential property or substance (often referred to as the "[[vital principle]]") distinct from any found in non-living matter, and it was thought that only living beings could produce the molecules of life.<ref>[[#Fiske|Fiske]] (1890), pp. 419–20.</ref> In 1828, [[Friedrich Wöhler]] published a paper on his [[serendipitous]] [[urea]] [[Wöhler synthesis|synthesis]] from [[potassium cyanate]] and [[ammonium sulfate]]; some regarded that as a direct overthrow of vitalism and the establishment of [[organic chemistry]].<ref>{{Cite journal|last=Wöhler|first=F.|date=1828|title=Ueber künstliche Bildung des Harnstoffs|journal=Annalen der Physik und Chemie|volume=88|issue=2|pages=253–256|doi=10.1002/andp.18280880206|bibcode=1828AnP....88..253W|issn=0003-3804}}</ref><ref name="Kauffman 20012">[[#Kauffman|Kauffman]] (2001), pp. 121–133.</ref>  However, the Wöhler synthesis has sparked controversy as some reject the death of vitalism at his hands.<ref>{{Cite journal|last=Lipman|first=Timothy O.|date=August 1964|title=Wohler's preparation of urea and the fate of vitalism|journal=Journal of Chemical Education|volume=41|issue=8|page=452|doi=10.1021/ed041p452|bibcode=1964JChEd..41..452L|issn=0021-9584}}</ref>  Since then, biochemistry has advanced, especially since the mid-20th century, with the development of new techniques such as [[chromatography]], [[X-ray diffraction]], [[dual polarisation interferometry]], [[protein nuclear magnetic resonance spectroscopy|NMR spectroscopy]], [[radioisotopic labeling]], [[electron microscope|electron microscopy]] and [[molecular dynamics]] simulations. These techniques allowed for the discovery and detailed analysis of many molecules and [[metabolic pathway]]s of the [[cell (biology)|cell]], such as [[glycolysis]] and the [[Krebs cycle]] (citric acid cycle), and led to an understanding of biochemistry on a molecular level.<ref>{{Cite journal |last1=Krebs |first1=H. A. |last2=Johnson |first2=W. A. |date=April 1937 |title=Metabolism of ketonic acids in animal tissues |journal=The Biochemical Journal |volume=31 |issue=4 |pages=645–660 |doi=10.1042/bj0310645 |issn=0264-6021 |pmc=1266984 |pmid=16746382}}</ref><ref>{{Cite journal |last1=Grüning |first1=Nana-Maria |last2=Ralser |first2=Markus |date=December 2021 |title=Glycolysis: How a 300yr long research journey that started with the desire to improve alcoholic beverages kept revolutionizing biochemistry |url=https://www.sciencedirect.com/science/article/pii/S2452310021000743#sec6 |journal=Current Opinion in Systems Biology |volume=28 |article-number=100380 |doi=10.1016/j.coisb.2021.100380 |via=Elsevier Science Direct}}</ref>

Another significant historic event in biochemistry is the discovery of the [[gene]], and its role in the transfer of information in the cell. In the 1950s, [[James D. Watson]], [[Francis Crick]], [[Rosalind Franklin]] and [[Maurice Wilkins]] were instrumental in solving [[DNA structure]] and suggesting its relationship with the genetic transfer of information.<ref>[[#Tropp|Tropp]] (2012), pp. 19–20.</ref> In 1958, [[George Beadle]] and [[Edward Tatum]] received the [[Nobel Prize]] for work in fungi showing that [[one gene–one enzyme hypothesis|one gene produces one enzyme]].<ref name="Krebs 2012">[[#Krebs|Krebs]] (2012), p. 32.</ref> In 1988, [[Colin Pitchfork]] was the first person convicted of murder with [[DNA]] evidence, which led to the growth of [[forensic science]].<ref name="Butler 2009">[[#Butler|Butler]] (2009), p. 5.</ref> More recently, [[Andrew Z. Fire]] and [[Craig C. Mello]] received the [[Nobel Prize in Physiology or Medicine|2006 Nobel Prize]] for discovering the role of [[RNA interference]] (RNAi) in the silencing of [[gene expression]].<ref name="Sen 2007">[[#Chandan|Chandan]] (2007), pp. 193–194.</ref>

== <span class="anchor" id="CHNOPS"></span> The chemical elements of life ==
[[Image:201 Elements of the Human Body.02.svg|thumb|upright|The main elements that compose the human body shown from most abundant (by mass) to least abundant]]
{{Main|Composition of the human body|Dietary mineral}}
{{Redirect|CHON||Chon (disambiguation)}}

Around two dozen [[chemical elements]] are essential to various kinds of [[life|biological life]]. Most rare elements on Earth are not needed by life (exceptions being  [[selenium]] and [[iodine]]),<ref>{{cite book |last1=Cox |first1=Michael M. |last2=Nelson |first2=David L. |last3=Lehninger |first3=Albert L. |title=Lehninger Principles of Biochemistry |date=2008 |publisher=Macmillan |ISBN=978-0716771081
}}</ref> while a few common ones ([[aluminium]] and [[titanium]]) are not used. Most organisms share element needs, but there are a few differences between [[plants]] and [[animals]]. For example, ocean algae use [[bromine]],<ref>{{Cite journal |last1=Liu |first1=Ming |last2=Hansen |first2=Poul Erik |last3=Lin |first3=Xiukun |date=2011 |title=Bromophenols in marine algae and their bioactivities |journal=Marine Drugs |volume=9 |issue=7 |pages=1273–1292 |doi=10.3390/md9071273  |doi-access=free|issn=1660-3397 |pmc=3148503 |pmid=21822416}}</ref> and land animals incorporate ionic bromide in their connective tissue,<ref>{{Cite journal |last1=McCall |first1=A. Scott |last2=Cummings |first2=Christopher F. |last3=Bhave |first3=Gautam |last4=Vanacore |first4=Roberto |last5=Page-McCaw |first5=Andrea |last6=Hudson |first6=Billy G. |date=2014-06-05 |title=Bromine is an essential trace element for assembly of collagen IV scaffolds in tissue development and architecture |journal=Cell |volume=157 |issue=6 |pages=1380–1392 |doi=10.1016/j.cell.2014.05.009 |issn=1097-4172 |pmc=4144415 |pmid=24906154 |bibcode=2014Cell..157.1380M }}</ref> but it is non-essential for land plants and can even be problematic at high quantities.<ref>{{Cite journal |last1=Leri |first1=Alessandra C. |last2=Hettithanthri |first2=Oshadi |last3=Bolan |first3=Shiv |last4=Zhang |first4=Tao |last5=Unrine |first5=Jason |last6=Myneni |first6=Satish |last7=Nachman |first7=Danielle R. |last8=Tran |first8=Huu Tuan |last9=Phillips |first9=Ankur J. |last10=Hou |first10=Deyi |last11=Wang |first11=Yidong |last12=Vithanage |first12=Meththika |last13=Padhye |first13=Lokesh P. |last14=Jasemi Zad |first14=Tahereh |last15=Heitz |first15=Anna |date=2024-05-05 |title=Bromine contamination and risk management in terrestrial and aquatic ecosystems |journal=Journal of Hazardous Materials |volume=469 |article-number=133881 |doi=10.1016/j.jhazmat.2024.133881 |issn=1873-3336 |pmc=11380803 |pmid=38422740 |bibcode=2024JHzM..46933881L }}</ref> All animals require [[sodium]],<ref>{{Cite journal |last1=Kaushik |first1=Shivam |last2=Kumar |first2=Rahul |last3=Kain |first3=Pinky |date=2018 |title=Salt an Essential Nutrient: Advances in Understanding Salt Taste Detection Using Drosophila as a Model System |journal=Journal of Experimental Neuroscience |volume=12 |article-number=1179069518806894 |doi=10.1177/1179069518806894 |issn=1179-0695 |pmc=6249657 |pmid=30479487}}</ref> but it is only an essential element for a small subset of plants, although many others do grow better in its presence (see [[sodium in biology]] for more).<ref>{{Cite journal |last1=Subbarao |first1=G. V. |last2=Ito |first2=O. |last3=Berry |first3=W. L. |last4=Wheeler |first4=R. M. |date=2003-09-01 |title=Sodium—A Functional Plant Nutrient |url=https://doi.org/10.1080/07352680390243495 |journal=Critical Reviews in Plant Sciences |publisher=Taylor & Francis |volume=22 |issue=5 |pages=391–416 |doi=10.1080/07352680390243495 |bibcode=2003CRvPS..22..391S |issn=0735-2689}}</ref> Plants need [[boron]] and [[silicon]], but animals may not (or may need ultra-small amounts).<ref>{{Cite journal |last1=Sheng |first1=Huachun |last2=Lei |first2=Yuyan |last3=Wei |first3=Jing |last4=Yang |first4=Zhengming |last5=Peng |first5=Lianxin |last6=Li |first6=Wenbing |last7=Liu |first7=Yuan |date=2024 |title=Analogy of silicon and boron in plant nutrition |journal=Frontiers in Plant Science |volume=15 |article-number=1353706 |doi=10.3389/fpls.2024.1353706 |doi-access=free |issn=1664-462X |pmc=10877001 |pmid=38379945|bibcode=2024FrPS...1553706S }}</ref>

Biomolecules are constructed from just six bulk macronutrients, abbreviated '''CHNOPS''' ([[carbon]], [[hydrogen]], [[nitrogen]], [[oxygen]], [[phosphorus]], and [[sulfur]]), and these six make up >99% of the mass of all of our cells.<ref>{{Cite web |title=CHNOPS: Elements of Life |url=https://www.socratica.com/pages/chnops-elements-of-life |access-date=2026-06-26 |website=Socratica |language=en}}</ref><ref>{{Cite journal |last1=Remick |first1=Kaleigh A. |last2=Helmann |first2=John D. |date=2023 |title=The elements of life: A biocentric tour of the periodic table |journal=Advances in Microbial Physiology |volume=82 |pages=1–127 |doi=10.1016/bs.ampbs.2022.11.001 |issn=2162-5468 |pmc=10727122 |pmid=36948652}}</ref> Humans further require significant quantities of four key ions ([[magnesium]], [[potassium]], [[sodium]], and [[calcium]]) and smaller amounts of some other elements and ions, termed [[Micronutrient|micronutrients]].<ref>{{Cite journal |last1=Remick |first1=Kaleigh A. |last2=Helmann |first2=John D. |date=2023 |title=The elements of life: A biocentric tour of the periodic table |journal=Advances in Microbial Physiology |volume=82 |pages=1–127 |doi=10.1016/bs.ampbs.2022.11.001 |issn=2162-5468 |pmc=10727122 |pmid=36948652}}</ref> In addition to the six major elements that compose most of the human body, humans require smaller amounts of possibly 18 more (see [[composition of the human body]] for a complete list).<ref>[[#Nielsen|Nielsen]] (1999), pp. 283–303.</ref>

==Biomolecules==
{{Main|Biomolecule}}
The four main classes of molecules in biochemistry (often called [[biomolecule]]s) are [[carbohydrate]]s, [[lipid]]s, [[protein]]s, and [[nucleic acid]]s.<ref name="slabaugh">[[#Slabaugh|Slabaugh]] (2007), pp. 3–6.</ref> Many biological molecules are [[polymer]]s: chains of smaller repeating units called [[monomer]]s. When monomers are linked together to synthesize a [[biopolymer|biological polymer]], they undergo a process called [[Dehydration reaction|dehydration synthesis]].<ref>{{Cite journal |last1=Runnels |first1=Calvin M. |last2=Lanier |first2=Kathryn A. |last3=Williams |first3=Justin Krish |last4=Bowman |first4=Jessica C. |last5=Petrov |first5=Anton S. |last6=Hud |first6=Nicholas V. |last7=Williams |first7=Loren Dean |date=2018-12-01 |title=Folding, Assembly, and Persistence: The Essential Nature and Origins of Biopolymers |url=https://doi.org/10.1007/s00239-018-9876-2 |journal=Journal of Molecular Evolution |volume=86 |issue=9 |pages=598–610 |doi=10.1007/s00239-018-9876-2 |issn=1432-1432 |pmc=6267704 |pmid=30456440 |bibcode=2018JMolE..86..598R }}</ref> Macromolecules can assemble in larger complexes with other molecules of the same or different type, often required for [[biological activity]].

===Carbohydrates===
{{Main|Carbohydrate|Monosaccharide|Disaccharide|Polysaccharide}}
<div class='skin-invert-image'>{{multiple image
| align     = right
| direction = vertical
| header    = [[Carbohydrates]]
| image1    = Beta-D-Glucose.svg
| width1    = 220
| caption1 = Glucose, a [[monosaccharide]]
| image2   = Saccharose2.svg
| width2   = 220
| caption2 = A molecule of [[sucrose]] ([[glucose]] + [[fructose]]), a [[disaccharide]]
| image3   = Amylose 3Dprojection.svg
| width3   = 220
| caption3 =[[Amylose]],  a [[polysaccharide]] made up of several thousand [[glucose]] units
}}</div>
Two of the main functions of carbohydrates are energy storage and providing structure. The term 'sugar' typically refers to mono- and disaccharides (defined below), which fall into the former category and taste sweet.<ref>{{Cite web |title=A Background on Carbohydrates and Sugars |url=https://ific.org/insights/background_on_carbohydrates_sugars/ |access-date=2026-09-04 |website=IFIC |language=en-US}}</ref> There are more carbohydrates on Earth than any other known type of biomolecule; they are used to store energy and [[Deoxyribose|genetic information]], as well as play important roles in cell to [[Cell–cell interaction|cell interactions]] and [[Cell signaling|communications]].<ref>{{cite journal |last=Chandel |first=Navdeep S. |title=Carbohydrate Metabolism | journal=Cold Spring Harbor Perspectives in Biology |date=2021 |volume=13 |issue=1 |article-number=a040568 | doi=10.1101/cshperspect.a040568 |pmid=33397651 | url=https://cshperspectives.cshlp.org/content/13/1/a040568 |access-date=8 January 2026|pmc=7778149 }}</ref> Carbohydrates generally have ratios of carbon:hydrogen:oxygen of 1:2:1, meaning a 1:1 ratio of carbon atoms to water (H<sub>2</sub>O), from which the term "carbohydrate" derives. 

The simplest type of carbohydrate is a [[monosaccharide]], which have the chemical formula C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> but vary in their precise structures<sub>.</sub><ref>{{Citation |last1=Holesh |first1=Julie E. |title=Physiology, Carbohydrates |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK459280/ |access-date=2026-09-04 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29083823 |last2=Aslam |first2=Sanah |last3=Martin |first3=Andrew}}</ref> [[Glucose]], [[fructose]], and [[galactose]] are [[Hexose|hexoses]], i.e. 6-carbon sugar, sharing the formula C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>, but varying in precise structure.<ref name=":0">{{Cite book |last1=Cox |first1=Michael |url=https://www.researchgate.net/publication/48376766 |title=Lehninger Principles of Biochemistry |last2=Nelson |first2=David |date=2000-01-01 |isbn=978-3-662-08290-4 |volume=5 |doi=10.1007/978-3-662-08289-8 |doi-broken-date=4 September 2026 }}</ref> A well-known [[pentose]], or 5-carbon sugar, is [[deoxyribose]] (C<sub>5</sub>H<sub>10</sub>O<sub>4</sub>), a component of [[DNA]].  A monosaccharide can switch between [[Open-chain compound|acyclic (open-chain) form]] and [[cyclic compound|cyclic]] form.<ref name=":0" /> This occurs through reaction of one of the [[Hydroxy group|hydroxyl groups]] with the [[carbonyl group]] on the end of the linear form, bridging them with an oxygen atom and releasing a water molecule in the process.<ref name=":0" /> The cyclic molecule has a [[hemiacetal]] or [[hemiketal]] group, depending on whether the linear form was an [[aldose]] or a [[ketose]], which describe the position of the carbonyl group to begin with.<ref>[[#Voet|Voet]] (2005), pp. 358–359.</ref>

In these cyclic forms, the ring usually has '''5''' or '''6''' atoms. These forms are called [[furanose]]s and [[pyranose]]s, respectively—by analogy with [[furan]] and [[pyran]], the simplest compounds with the same carbon-oxygen ring (although they lack the carbon-carbon [[double bond]]s of these two molecules).<ref name=":0" /> For example, the aldohexose [[glucose]] may form a hemiacetal linkage between the hydroxyl on carbon 1 and the oxygen on carbon 4, yielding a molecule with a 5-membered ring, called [[glucofuranose]].  The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called [[glucopyranose]]. Notice that this means that pentoses/furanoses, and hexoses/pyranoses, are not interchangeable pairs: the number of carbons in the molecule can be different from the number of atoms in the ring, as not all carbons are necessarily included in the ring backbone.<ref name=":0" />

Two monosaccharides can be joined by a [[Glycosidic bond|glycosidic]] or [[ester bond]] into a ''[[disaccharide]]'' through a [[dehydration reaction]] during which a molecule of water is released. The reverse reaction in which the glycosidic bond of a disaccharide is broken into two monosaccharides is termed ''[[hydrolysis]]''.<ref name=":0" /> The best-known disaccharide is [[sucrose]] or ordinary [[sugar]], which consists of a [[glucose]] molecule and a [[fructose]] molecule joined.<ref>{{Cite web |last=PubChem |title=Sucrose |url=https://pubchem.ncbi.nlm.nih.gov/compound/5988 |access-date=2026-09-04 |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref> Another important disaccharide is [[lactose]], found in milk, consisting of a glucose molecule and a [[galactose]] molecule.<ref name=":1">{{Cite web |last=PubChem |title=(+)-Lactose |url=https://pubchem.ncbi.nlm.nih.gov/compound/440995 |access-date=2026-09-04 |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref> Lactose may be hydrolysed by [[lactase]], and deficiency in this enzyme results in [[lactose intolerance]].

When a few (around three to six) monosaccharides are joined, it is called an ''[[oligosaccharide]]'' (''oligo-'' meaning "few"). These molecules tend to be used as markers and [[Cell signaling|signals]], as well as having some other uses.<ref name="Varki_1999">[[#Varki|Varki]] (1999), p. 17.</ref> When larger groups are joined, this is called a [[polysaccharide]]. They can be joined in one long linear chain, or they may be [[Branching (polymer chemistry)|branched]].<ref name=":0" /> Two of the most common polysaccharides are [[cellulose]] and [[glycogen]], both consisting of repeating glucose [[monomer]]s. ''Cellulose'' is an important structural component of plant's [[cell wall]]s and ''[[glycogen]]'' is used as a form of energy storage in animals. The energy storage polysaccharide in plants is called [[starch]]. 

[[Sugar]] can be characterized by having [[Reducing sugar|reducing]] or non-reducing ends. A [[reducing end]] of a carbohydrate is a carbon atom that can be in equilibrium with the open-chain [[aldehyde]] ([[aldose]]) or keto form ([[ketose]]). If the joining of monomers takes place at such a carbon atom, the free [[hydroxy group]] of the [[pyranose]] or [[furanose]] form is exchanged with an OH-side-chain of another sugar, yielding a full [[acetal]]. This prevents opening of the chain to the aldehyde or keto form and renders the modified residue non-reducing.<ref name=":0" /> Lactose contains a reducing end at its glucose moiety, whereas the galactose moiety forms a full acetal with the C4-OH group of glucose.<ref name=":1" /> [[Saccharose]] does not have a reducing end because of full acetal formation between the aldehyde carbon of glucose (C1) and the keto carbon of fructose (C2).

===Lipids===
{{Main|Lipid|Glycerol|Fatty acid}}

[[File:Common lipid types.svg|class=skin-invert-image|thumb|Structures of some common lipids. At the top are [[cholesterol]] and [[oleic acid]].<ref>[[#Stryer|Stryer]] (2007), p. 328.</ref> The middle structure is a [[triglyceride]] composed of [[oleate|oleoyl]], [[stearic acid|stearoyl]], and [[palmitate|palmitoyl]] chains attached to a [[glycerol]] backbone. At the bottom is the common [[phospholipid]], [[phosphatidylcholine]].<ref>[[#Voet|Voet]] (2005), Ch. 12 Lipids and Membranes.</ref>]]

[[Lipid|'''Lipids''']] comprise a diverse range of [[molecules]] defined by being relatively water-insoluble or [[nonpolar]] compounds of biological origin, including [[wax]]es, [[fatty acid]]s, fatty-acid derived [[phospholipid]]s, [[sphingolipid]]s, [[glycolipid]]s, and [[terpenoid]]s (e.g., [[retinoid]]s and [[steroid]]s). This makes them unique from the other groups of biomolecules as they are defined by a property, rather than structure.<ref name=":0" /> This makes them a diverse group. Some lipids are linear, open-chain [[aliphatic]] molecules, while others have ring structures. Some are [[aromatic]] (with a cyclic [ring] and planar [flat] structure) while others are not. Some are flexible, while others are rigid.<ref>{{Citation |last1=Ahmed |first1=Saba |title=Biochemistry, Lipids |date=2023 |url=https://www.ncbi.nlm.nih.gov/books/NBK525952/ |work=StatPearls |access-date=2023-11-30 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30247827 |last2=Shah |first2=Parini |last3=Ahmed |first3=Owais}}</ref>

Lipids are extremely structurally diverse. Some commonly encountered lipids, such as [[triglyceride]]s, the main group of bulk lipids, and [[Phospholipid|phospholipids]], a major component of [[Cell membrane|cell membranes]], are comprised of a [[glycerol]] backbone bound to [[Fatty acid|fatty acids]] (3 for the former, 2 for the latter). Fatty acids may be [[Saturated and unsaturated compounds|saturated]] (no [[double bond]]s in the carbon chain) or unsaturated (one or more double bonds in the carbon chain).<ref name=":0" /> Fatty acids are often considered the simplest lipids, and the smallest fatty acids, short chain fatty acids (SCFAs), are noted for their health benefits.<ref>{{Cite journal |last1=Mukhopadhya |first1=Indrani |last2=Louis |first2=Petra |date=October 2025 |title=Gut microbiota-derived short-chain fatty acids and their role in human health and disease |url=https://www.nature.com/articles/s41579-025-01183-w |journal=Nature Reviews Microbiology |language=en |publisher=Nature Publishing Group |volume=23 |issue=10 |pages=635–651 |doi=10.1038/s41579-025-01183-w |pmid=40360779 |issn=1740-1534}}</ref> However, many more lipids exist that do not follow this pattern, hence they are not considered polymers since there is no one repeating molecule found across all lipids.<ref>{{Citation |title=4.4 Lipids |date=2025-03-05 |work=Biology and Chemistry for Human Biosciences |url=https://rmit.pressbooks.pub/biologyandchemistryhumanbiosciences/chapter/lipids/ |access-date=2026-09-04 |archive-url=http://web.archive.org/web/20260518034557/https://rmit.pressbooks.pub/biologyandchemistryhumanbiosciences/chapter/lipids/ |archive-date=2026-05-18 |publisher=RMIT Open Press |language=en}}</ref> Consequently, components like fatty acids, glycerol, and in other lipid types, [[Sphingosine|sphingosines]], are not monomers. Consider, for example, cholesterol: a lipid without any of these "building block" molecules, instead consisting of a few nonpolar rings fused together and some functional groups extending off.<ref>{{Cite web |title=Cholesterol (C27H46O) |url=http://pubchemlite.lcsb.uni.lu/e/compound/5997 |access-date=2026-09-04 |website=pubchemlite.lcsb.uni.lu |language=en}}</ref>

Most lipids are largely nonpolar but may have some [[Polar molecule|polar]] character. In general, the bulk of their structure is nonpolar or [[hydrophobic]] ("water-fearing"), meaning that it does not interact well with polar solvents like [[water]]. Some lipids, such as fatty acids and membrane-forming phospholipids, have a polar or [[hydrophilic]] ("water-loving") head group which will tend to associate with polar solvents like water. This makes them [[amphiphilic]] molecules (having both hydrophobic and hydrophilic portions). In the case of [[cholesterol]], the polar group is a mere –OH (hydroxyl or alcohol).<ref>{{Cite web |last=PhD |first=Chris Masterjohn |date=2008-11-09 |title=Cholesterol's Hydroxyl Group |url=https://chrismasterjohnphd.substack.com/p/cholesterols-hydroxyl-group |access-date=2025-08-29 |website=Harnessing the Power of Nutrients}}</ref> Phospholipids often have larger and more diverse polar head groups.<ref name=":0" /> 

Lipids are an integral part of our daily diet. Most [[oil]]s and [[milk product]]s that we use for cooking and eating like [[butter]], [[cheese]], [[ghee]] etc. are composed of [[fat]]s, which can refer to a broader class of lipids, but in nutrition and food science refers to the triglycerides we eat.<ref>{{Cite web |title=Dietary fat and your health {{!}} HealthLink BC |url=https://www.healthlinkbc.ca/healthlinkbc-files/dietary-fat-and-your-health |access-date=2026-09-04 |website=www.healthlinkbc.ca}}</ref><ref name=":2">{{Cite journal |last1=Petersen |first1=Kristina S. |last2=Maki |first2=Kevin C. |last3=Calder |first3=Philip C. |last4=Belury |first4=Martha A. |last5=Messina |first5=Mark |last6=Kirkpatrick |first6=Carol F. |last7=Harris |first7=William S. |date=2024-10-28 |title=Perspective on the health effects of unsaturated fatty acids and commonly consumed plant oils high in unsaturated fat |journal=The British Journal of Nutrition |volume=132 |issue=8 |pages=1039–1050 |doi=10.1017/S0007114524002459 |issn=1475-2662 |pmc=11600290 |pmid=39475012}}</ref> [[Vegetable oil]]s are rich in various [[polyunsaturated fatty acid]]s (PUFA) which may exert cardioprotective effects, although evidence is still inconclusive as to their overall impact on health.<ref name=":2" /> Lipid-containing foods undergo digestion within the body and are broken into fatty acids and glycerol, the final degradation products of triglycerides. Lipids, especially [[phospholipid]]s, are also used in various [[pharmaceutical product]]s, either as co-solubilizers (e.g. in parenteral infusions) or else as [[drug carrier]] components (e.g. in a [[liposome]] or [[transfersome]]).<ref>{{Cite web |title=View of Lipids in pharmaceutical and cosmetic preparations |url=https://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/view/409/412 |archive-url=http://web.archive.org/web/20240130180012/https://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/view/409/412 |archive-date=2024-01-30 |access-date=2026-09-04 |website=grasasyaceites.revistas.csic.es |language=en-US}}</ref><ref>{{Cite journal |last1=Antonara |first1=Lefkothea |last2=Triantafyllopoulou |first2=Efstathia |last3=Chountoulesi |first3=Maria |last4=Pippa |first4=Natassa |last5=Dallas |first5=Paraskevas P. |last6=Rekkas |first6=Dimitrios M. |date=2025-08-28 |title=Lipid-Based Drug Delivery Systems: Concepts and Recent Advances in Transdermal Applications |journal=Nanomaterials |location=Basel, Switzerland |volume=15 |issue=17 |pages=1326 |doi=10.3390/nano15171326  |doi-access=free|issn=2079-4991 |pmc=12430098 |pmid=40938004}}</ref>

===Proteins===
{{Main|Protein|Amino acid}}

[[File:AminoAcidball.svg|thumbnail|The general structure of an α-amino acid, with the [[amine|amino]] group on the left and the [[carboxyl]] group on the right]]

[[Protein]]s are polymers made from monomers called [[amino acid]]s. An amino acid consists of an alpha carbon atom attached to an [[amino]] group, –NH<sub>2</sub>, a [[carboxylic acid]] group, –COOH (although these exist as –NH<sub>3</sub><sup>+</sup> and –COO<sup>−</sup> under physiologic conditions), a simple [[hydrogen atom]], and a side chain commonly denoted as "–R". The side chain  "R" is different for each amino acid of which there are 20 [[proteinogenic amino acid|standard ones]].  It is this "R" group that makes each amino acid different, and the properties of the side chains greatly influence the overall [[Protein tertiary structure|three-dimensional conformation]] of a protein.<ref name=":0" /> Some amino acids have functions by themselves or in a modified form; for instance, [[glutamate]] functions as an important [[neurotransmitter]].<ref>{{Cite journal |last=Pal |first=Mia Michaela |date=2021 |title=Glutamate: The Master Neurotransmitter and Its Implications in Chronic Stress and Mood Disorders |journal=Frontiers in Human Neuroscience |volume=15 |article-number=722323 |doi=10.3389/fnhum.2021.722323  |doi-access=free|issn=1662-5161 |pmc=8586693 |pmid=34776901}}</ref> To form proteins, they react via [[Dehydration reaction|dehydration]] synthesis which removes a [[water molecule]] and forms a [[peptide bond]] between the [[nitrogen]] of one amino acid's amino group and the carbon of the other's carboxylic acid group. The resulting molecule is called a ''[[dipeptide]]'', and short stretches of amino acids (usually, fewer than thirty) are called ''[[peptides]]'' or [[polypeptides]]. Longer stretches merit the title ''proteins''. As an example, the important blood [[blood plasma|serum]] protein [[human serum albumin|albumin]] contains 585 [[Protein structure|amino acid residues]].<ref name="Metzler 2001">[[#Metzler|Metzler]] (2001), p. 58.</ref>
[[File:Amino acids 1.png|thumb|left|Generic amino acids (1) in neutral form, (2) as they exist physiologically, and (3) joined as a dipeptide]]

[[File:1GZX Haemoglobin.png|thumb|A schematic of [[hemoglobin]]. The red and blue ribbons represent the protein [[globin]]; the green structures are the [[heme]] groups.]]
Proteins can have structural and/or functional roles. For instance, movements of the proteins [[actin]] and [[myosin]] ultimately are responsible for the contraction of skeletal muscle.<ref>{{Cite journal |last=Squire |first=John |date=2019-11-14 |title=Special Issue: The Actin-Myosin Interaction in Muscle: Background and Overview |journal=International Journal of Molecular Sciences |volume=20 |issue=22 |pages=5715 |doi=10.3390/ijms20225715  |doi-access=free|issn=1422-0067 |pmc=6887992 |pmid=31739584}}</ref> One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be ''extremely'' selective in what they bind. [[Antibody|Antibodies]] are an example of proteins that attach to one specific type of molecule. Antibodies are composed of two heavy and two light chains which are linked by [[disulfide linkage]]s between specific cysteine residues. Antibodies are specific through variation based on differences in the N-terminal domain, which allows them to bind immunological antigens strongly.<ref>{{cite journal |doi=10.1016/j.tibs.2009.11.005 |pmid=20022755 |pmc=4716677 |title=How antibodies fold |journal=Trends in Biochemical Sciences |volume=35 |issue=4 |pages=189–198 |year=2010 |last1=Feige |first1=Matthias J. |last2=Hendershot |first2=Linda M. |last3=Buchner |first3=Johannes }}</ref><ref>{{Cite book |last1=Jr |first1=Charles A. Janeway |url=https://www.ncbi.nlm.nih.gov/books/NBK10757/ |title=Immunobiology |last2=Travers |first2=Paul |last3=Walport |first3=Mark |last4=Shlomchik |first4=Mark J. |last5=Jr |first5=Charles A. Janeway |last6=Travers |first6=Paul |last7=Walport |first7=Mark |last8=Shlomchik |first8=Mark J. |date=2001 |publisher=Garland Science |isbn=978-0-8153-3642-6 |edition=5th}}</ref> The [[enzyme-linked immunosorbent assay]] (ELISA), which uses antibodies, is one of the most sensitive tests modern medicine uses to detect various biomolecules. 

Probably the most important proteins, however, are the [[enzyme]]s. Virtually every reaction in a living cell requires an enzyme to lower the [[activation energy]] of the reaction. These molecules recognize specific reactant molecules called ''[[substrate (biochemistry)|substrates]]''; they then [[Catalysis|catalyze]] the reaction between them. By lowering the [[activation energy]], the enzyme speeds up that reaction by a rate of 10<sup>11</sup> or more; a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process and is free to catalyze the same reaction with a new set of substrates. Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.<ref name=":0" />

The structure of proteins is traditionally described in a hierarchy of four levels. The [[primary structure]] of a protein consists of its linear sequence of amino acids; for instance, "alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-lysine-...". [[Secondary structure]] is concerned with local morphology (morphology being the study of structure). Some combinations of amino acids will tend to curl up in a coil called an [[alpha helix|α-helix]] or into a sheet called a [[Beta sheet|β-sheet]]; some α-helixes can be seen in the hemoglobin schematic above. [[Tertiary structure]] is the entire three-dimensional shape of the protein. This shape is determined by the sequence of amino acids. In fact, a single change can change the entire structure. For example, the beta chain of hemoglobin contains 146 amino acid residues; substitution of the [[glutamate]] residue at position 6 with a [[valine]] residue changes the behavior of hemoglobin so much that it results in [[sickle-cell disease]].<ref>{{Cite journal |last1=Inusa |first1=Baba P. D. |last2=Hsu |first2=Lewis L. |last3=Kohli |first3=Neeraj |last4=Patel |first4=Anissa |last5=Ominu-Evbota |first5=Kilali |last6=Anie |first6=Kofi A. |last7=Atoyebi |first7=Wale |date=May 2019 |title=Sickle Cell Disease-Genetics, Pathophysiology, Clinical Presentation and Treatment |journal=International Journal of Neonatal Screening |volume=5 |issue=2 |pages=20 |doi=10.3390/ijns5020020  |doi-access=free|issn=2409-515X |pmc=7510211 |pmid=33072979}}</ref> Finally, [[quaternary structure]] is how separately polypeptide chains interact with one another to form the final protein. This only applied to proteins comprised of multiple chains, such as hemoglobin with its four subunits, whereas many others have only one chain.<ref>[[#Fromm|Fromm and Hargrove]] (2012), pp. 35–51.</ref>

[[File:Protein structure examples.png|thumb|Examples of protein structures from the [[Protein Data Bank]]]]
[[File:Structural coverage of the human cyclophilin family.png|thumb|Members of a protein family, as represented by the structures of the [[isomerase]] [[protein domain|domains]]]]
Ingested proteins are usually broken up into single amino acids or dipeptides in the [[small intestine]] and then absorbed. They can then be joined to form new proteins. Intermediate products of glycolysis, the citric acid cycle, and the [[pentose phosphate pathway]] can be used to form all twenty amino acids, and most bacteria and plants possess all the necessary enzymes to synthesize them (see more in [[amino acid synthesis]]). Humans and other mammals, however, can synthesize only half of them. They cannot synthesize [[isoleucine]], [[leucine]], [[lysine]], [[methionine]], [[phenylalanine]], [[threonine]], [[tryptophan]], [[histidine]], and [[valine]]. Because they must be ingested, these are the [[essential amino acid]]s.<ref>{{Citation |last1=Lopez |first1=Michael J. |title=Biochemistry, Essential Amino Acids |date=2024-04-30 |work=StatPearls [Internet] |url=https://www.ncbi.nlm.nih.gov/sites/books/NBK557845/ |access-date=2026-09-04 |publisher=StatPearls Publishing |language=en |pmid=32496725 |last2=Mohiuddin |first2=Shamim S.}}</ref> Mammals do possess the enzymes to synthesize [[alanine]], [[asparagine]], [[aspartate]], [[cysteine]], [[glutamate]], [[glutamine]], [[glycine]], [[proline]], [[serine]], and [[tyrosine]], the nonessential amino acids. While they can synthesize [[arginine]], they cannot produce it in sufficient amounts for young, growing animals, and so these are often considered essential amino acids as well.<ref>{{Cite journal |last1=Wu |first1=Guoyao |last2=Bazer |first2=Fuller W. |last3=Davis |first3=Teresa A. |last4=Kim |first4=Sung Woo |last5=Li |first5=Peng |last6=Marc Rhoads |first6=J. |last7=Carey Satterfield |first7=M. |last8=Smith |first8=Stephen B. |last9=Spencer |first9=Thomas E. |last10=Yin |first10=Yulong |date=May 2009 |title=Arginine metabolism and nutrition in growth, health and disease |journal=Amino Acids |volume=37 |issue=1 |pages=153–168 |doi=10.1007/s00726-008-0210-y |issn=1438-2199 |pmc=2677116 |pmid=19030957}}</ref>

If the amino group is removed from an amino acid, it leaves behind a carbon skeleton called an α-[[keto acid]]. Enzymes called [[transaminase]]s can easily transfer the amino group from one amino acid (making it an α-keto acid) to another α-keto acid (making it an amino acid). This is important in the biosynthesis of amino acids, as for many of the pathways, intermediates from other biochemical pathways are converted to the α-keto acid skeleton, and then an amino group is added, often via [[transamination]]. The amino acids may then be linked together to form a protein.<ref>{{Citation |last1=Sánchez López de Nava |first1=Arturo |title=Physiology, Metabolism |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK546690/ |access-date=2026-09-04 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31536296 |last2=Raja |first2=Avais}}</ref>

Proteins are broken down by first hydrolyzing them into their component amino acids.<ref>{{Citation |last1=Gurina |first1=Tatyana S. |title=Biochemistry, Protein Catabolism |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK556047/ |access-date=2026-09-04 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32310507 |last2=Mohiuddin |first2=Shamim S.}}</ref> Further breakdown of these amino acids releases free [[ammonia]] (NH<sub>3</sub>), existing as the [[ammonium]] ion (NH<sub>4</sub><sup>+</sup>) in blood, which is toxic to life forms. A suitable method for excreting it must therefore exist. Different tactics have evolved in different animals, depending on the animals' needs. [[Unicellular]] organisms release the ammonia into the environment. Likewise, [[Osteichthyes|bony fish]] can release ammonia into the water where it is quickly diluted. In general, mammals convert ammonia into urea, via the [[urea cycle]].<ref>{{Cite book |last1=Molnar |first1=Charles |title=Concepts of Biology – 1st Canadian Edition |last2=Gair |first2=Jane |date=2015 |publisher=BCcampus |isbn=978-1-989623-99-2 |edition=1st |chapter=22.4. Nitrogenous Wastes}}</ref>

In order to determine whether two proteins are related, or in other words to decide whether they are homologous or not, scientists use sequence-comparison methods. Methods like [[sequence alignment]]s and [[structural alignment]]s are powerful tools that help scientists identify [[Sequence homology|homologies]] between related molecules.<ref>{{Cite web |title=Homology - Site Guide - NCBI |url=https://www.ncbi.nlm.nih.gov/guide/homology/ |access-date=2026-09-04 |website=www.ncbi.nlm.nih.gov}}</ref><ref>{{Cite journal |last=Pearson |first=William R. |date=June 2013 |title=An introduction to sequence similarity ("homology") searching |journal=Current Protocols in Bioinformatics |volume=Chapter 3 |pages=3.1.1–3.1.8 |doi=10.1002/0471250953.bi0301s42 |issn=1934-340X |pmc=3820096 |pmid=23749753}}</ref> Homology helps scientists understand the evolutionary relationships between proteins and extend understanding of their structure and thus their function.<ref>{{Cite journal |last=Gabaldón |first=Toni |date=2007-02-24 |title=Evolution of proteins and proteomes: a phylogenetics approach |journal=Evolutionary Bioinformatics Online |volume=1 |pages=51–61 |issn=1176-9343 |pmc=2658874 |pmid=19325853}}</ref><ref>{{Cite journal |last1=Hamp |first1=Tobias |last2=Kassner |first2=Rebecca |last3=Seemayer |first3=Stefan |last4=Vicedo |first4=Esmeralda |last5=Schaefer |first5=Christian |last6=Achten |first6=Dominik |last7=Auer |first7=Florian |last8=Boehm |first8=Ariane |last9=Braun |first9=Tatjana |last10=Hecht |first10=Maximilian |last11=Heron |first11=Mark |last12=Hönigschmid |first12=Peter |last13=Hopf |first13=Thomas A. |last14=Kaufmann |first14=Stefanie |last15=Kiening |first15=Michael |date=2013 |title=Homology-based inference sets the bar high for protein function prediction |journal=BMC Bioinformatics |volume=14 Suppl 3 |issue=Suppl 3 |pages=S7 |doi=10.1186/1471-2105-14-S3-S7  |doi-access=free|issn=1471-2105 |pmc=3584931 |pmid=23514582}}</ref>

===Nucleic acids===
{{Main|Nucleic acid|DNA|RNA|Nucleotide}}
[[File:0322 DNA Nucleotides.jpg|thumbnail|The structure of [[deoxyribonucleic acid]] (DNA); the picture shows the monomers being put together.]]

[[Nucleic acids]], so-called because of their prevalence in cellular [[cell nucleus|nuclei]], is the generic name of this family of [[biopolymer]]s. They are complex, high-molecular-weight biochemical macromolecules that encode [[genetic information]] in all living cells and viruses.<ref name="Voet_2005"/> Their monomers are called [[nucleotide]]s, and each consists of three components: a nitrogenous heterocyclic [[base (chemistry)|base]] (either a [[purine]] or a [[pyrimidine]]), a pentose sugar, and a [[phosphate]] group.<ref>[[#Saenger|Saenger]] (1984), p. 84.</ref>

[[File:Nucleotides 1.svg|class=skin-invert-image|thumb|Structural elements of common nucleic acid constituents. Because they contain at least one phosphate group, the compounds marked ''nucleoside monophosphate'', ''nucleoside diphosphate'' and ''nucleoside triphosphate'' are all nucleotides (not phosphate-lacking [[nucleoside]]s).]]

The most common nucleic acids are [[deoxyribonucleic acid]] (DNA) and [[ribonucleic acid]] (RNA). The [[phosphate group]] and the sugar of each form nucleotide bonds to form the backbone of the nucleic acid, while the sequence of nitrogenous bases stores the information. The most common nitrogenous bases are [[adenine]], [[cytosine]], [[guanine]], [[thymine]], and [[uracil]]. The [[nitrogenous base]]s of each strand of a nucleic acid will form [[hydrogen bonds]] with a specific partner base in a complementary strand of nucleic acid. Adenine binds with thymine or uracil, and cytosine and guanine bind one another. Adenine, thymine, and uracil form two hydrogen bonds, while cytosine and guanine form three.<ref name=":0" />

Aside from the genetic material of the cell, nucleic acids often play a role as [[second messenger]]s, as well as forming the base molecule for [[adenosine triphosphate]] (ATP), the primary energy-carrier molecule found in all living organisms. Other nucleotides besides adenosine can also be found forming other, less common, energy-carrying molecules such as guanosine in [[Guanosine triphosphate|GTP]] or uracil in UTP. Also, while adenine, cytosine, and guanine occur in both RNA and DNA, thymine occurs only in DNA and uracil occurs in RNA.<ref name=":0" />

==Metabolism==

===Carbohydrates as energy source===
{{Main|Carbohydrate metabolism|Carbon cycle}}
Glucose is an energy source in most life forms. For instance, polysaccharides are broken down into their monomers by [[enzyme]]s ([[glycogen phosphorylase]] removes glucose residues from glycogen, a polysaccharide). Disaccharides like lactose or sucrose are cleaved into their two component monosaccharides.<ref>{{cite web |title=Disaccharide |url=https://www.britannica.com/science/disaccharide |access-date=14 October 2023 |website=Encyclopedia Britannica |archive-date=19 October 2023 |archive-url=https://web.archive.org/web/20231019212527/https://www.britannica.com/science/disaccharide |url-status=live }}</ref>

====Glycolysis (anaerobic)====
{{Glycolysis summary}}
Glucose is mainly metabolized by a very important ten-step [[Metabolic pathway|pathway]] called [[glycolysis]], the net result of which is to break down one molecule of glucose into two molecules of [[pyruvate]]. This also produces a net two molecules of [[Adenosine triphosphate|ATP]], the energy currency of cells, along with two reducing equivalents of converting [[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]] (nicotinamide adenine dinucleotide: oxidized form) to NADH (nicotinamide adenine dinucleotide: reduced form). This does not require oxygen; if no oxygen is available (or the cell cannot use oxygen), the NAD is restored by converting the pyruvate to [[lactic acid|lactate (lactic acid)]] (e.g. in humans) or to [[ethanol]] plus carbon dioxide (e.g. in [[yeast]]). Other monosaccharides like galactose and fructose can be converted into intermediates of the glycolytic pathway.<ref>[[#Fromm|Fromm and Hargrove]] (2012), pp. 163–180.</ref>

====Aerobic====
In [[aerobic glycolysis|aerobic]] cells with sufficient [[oxygen]], as in most human cells, the pyruvate is further metabolized. It is irreversibly converted to [[acetyl-CoA]], giving off one carbon atom as the waste product [[carbon dioxide]], generating another reducing equivalent as [[NADH]]. The two molecules acetyl-CoA (from one molecule of glucose) then enter the [[citric acid cycle]], producing two molecules of ATP, six more NADH molecules and two reduced (ubi)quinones (via [[FADH2|FADH<sub>2</sub>]] as enzyme-bound cofactor), and releasing the remaining carbon atoms as carbon dioxide. The produced NADH and quinol molecules then feed into the enzyme complexes of the respiratory chain, an [[electron transport system]] transferring the electrons ultimately to oxygen and conserving the released energy in the form of a proton gradient over a membrane ([[inner mitochondrial membrane]] in eukaryotes). Thus, oxygen is reduced to water and the original electron acceptors NAD<sup>+</sup> and [[quinone]] are regenerated. This is why humans breathe in oxygen and breathe out carbon dioxide. The energy released from transferring the electrons from high-energy states in NADH and quinol is conserved first as proton gradient and converted to ATP via ATP synthase. This generates an additional ''28'' molecules of ATP (24 from the 8 NADH + 4 from the 2 quinols), totaling to 32 molecules of ATP conserved per degraded glucose (two from glycolysis + two from the citrate cycle).<ref>[[#Voet|Voet]] (2005), Ch. 17 Glycolysis.</ref> It is clear that using oxygen to completely oxidize glucose provides an organism with far more energy than any oxygen-independent metabolic feature, and this is thought to be the reason why complex life appeared only after Earth's atmosphere accumulated large amounts of oxygen.

====Gluconeogenesis====
{{Main|Gluconeogenesis}}
In [[vertebrate]]s, vigorously contracting [[skeletal muscle]]s (during weightlifting or sprinting, for example) do not receive enough oxygen to meet the energy demand, and so they shift to [[Fermentation (biochemistry)|anaerobic metabolism]], converting glucose to lactate.
The combination of glucose from noncarbohydrates origin, such as fat and proteins. This only happens when [[glycogen]] supplies in the liver are worn out. The pathway is a crucial reversal of [[glycolysis]] from pyruvate to glucose and can use many sources like amino acids, glycerol and [[Krebs Cycle]]. Large scale protein and fat [[catabolism]] usually occur when those suffer from starvation or certain endocrine disorders.<ref>{{Cite book| editor-first1=Robert| editor-first2=Elizabeth| editor-last1=Hine| editor-last2=Martin| url=https://www.oxfordreference.com/view/10.1093/acref/9780198714378.001.0001/acref-9780198714378| isbn=978-0-19-871437-8| title=A Dictionary of Biology| date=17 September 2015| publisher=Oxford University Press| doi=10.1093/acref/9780198714378.001.0001| access-date=29 April 2020| archive-date=10 July 2020| archive-url=https://web.archive.org/web/20200710005409/https://www.oxfordreference.com/view/10.1093/acref/9780198714378.001.0001/acref-9780198714378| url-status=live}}</ref> The [[liver]] regenerates the glucose, using a process called [[gluconeogenesis]]. This process is not quite the opposite of glycolysis, and actually requires three times the amount of energy gained from glycolysis (six molecules of ATP are used, compared to the two gained in glycolysis). Analogous to the above reactions, the glucose produced can then undergo glycolysis in tissues that need energy, be stored as glycogen (or [[starch]] in plants), or be converted to other monosaccharides or joined into di- or oligosaccharides. The combined pathways of glycolysis during exercise, lactate's crossing via the bloodstream to the liver, subsequent gluconeogenesis and release of glucose into the bloodstream is called the [[Cori cycle]].<ref>[[#Fromm|Fromm and Hargrove]] (2012), pp. 183–194.</ref>

==Relationship to other "molecular-scale" biological sciences==
{{Multiple issues|section=y|
{{Unreferenced section|date=August 2023}}
{{Original research|section|reason=Section defines relationships between disciplines without citing any sources from those disciplines.|date=August 2023}}
}}
[[File:Schematic relationship between biochemistry, genetics and molecular biology.svg|thumb|Schematic relationship between biochemistry, [[genetics]], and [[molecular biology]]]]

Researchers in biochemistry use specific techniques native to biochemistry (for instance, [[enzyme kinetics]] or [[subcellular fractionation]]), but increasingly combine these with techniques and ideas developed in the fields of [[genetics]], [[molecular biology]], and [[biophysics]]. There is not a defined line between these disciplines. Biochemistry studies the [[chemistry]] required for biological activity of molecules, [[molecular biology]] studies those molecules' biological activity, and [[genetics]] studies their heredity, which happens to be carried by their [[genome]]. This is shown in the following schematic that depicts one possible view of the relationships between the fields:
* '''''Biochemistry''''' is the study of the chemical substances and vital processes occurring in live [[organism]]s. [[Biochemist]]s focus heavily on the role, function, and structure of [[Biomolecule|bio-molecules]]. The study of the chemistry behind biological processes and the synthesis of biologically active molecules are applications of biochemistry. Biochemistry studies life at the atomic and molecular level.
* '''''Genetics''''' is the study of the effect of genetic differences in organisms. This can often be inferred by the absence of a normal component (e.g. one [[gene]]). The study of "[[mutant]]s" – organisms that lack one or more functional components with respect to the so-called "[[wild type]]" or normal [[phenotype]]. Genetic interactions ([[epistasis]]) can often confound simple interpretations of such "[[Gene knockout|knockout]]" studies.
* '''''Molecular biology''''' is the study of molecular underpinnings of the biological phenomena, focusing on molecular synthesis, modification, mechanisms and interactions. The [[central dogma of molecular biology]], where genetic material is transcribed into [[RNA]] and then translated into [[protein]], despite being oversimplified, still provides a good starting point for understanding the field. This concept has been revised in light of emerging novel roles for RNA.
* '''''[[Chemical biology]]''''' seeks to develop new tools based on [[small molecule]]s that allow minimal perturbation of biological systems while providing detailed information about their function. Further, chemical biology employs biological systems to create non-natural hybrids between biomolecules and synthetic devices (for example, emptied [[viral capsid]]s that can deliver [[gene therapy]] or [[Pharmaceutical drug|drug molecules]]).

==See also==
{{Main|Outline of biochemistry}}

=== Lists ===
{{div col|colwidth=22em}}
* [[List of important publications in chemistry#Biochemistry|Important publications in biochemistry (chemistry)]]
* [[List of biochemistry topics]]
* [[List of biochemists]]
* [[List of biomolecules]]
{{div col end}}

=== See also ===
{{div col|colwidth=22em}}
* [[Astrobiology]]
* [[Biochemistry (journal)]]
* [[Biological Chemistry (journal)]]
* [[Biophysics]]
* [[Chemical ecology]]
* [[Computational biomodeling]]
* [[Dedicated bio-based chemical]]
* [[Enzyme Commission number|EC number]]
* [[Hypothetical types of biochemistry]]
* [[International Union of Biochemistry and Molecular Biology]]
* [[Metabolome]]
* [[Metabolomics]]
* [[Molecular biology]]
* [[Molecular medicine]]
* [[Plant biochemistry]]
* [[Proteolysis]]
* [[Small molecule]]
* [[Structural biology]]
* [[TCA cycle]]
{{div col end}}

==Notes==
{{Notelist}}

==References==
{{Reflist}}

=== Cited literature ===
{{refbegin|30em}}
* {{cite book |ref=Amsler |author=Amsler, Mark |url=https://books.google.com/books?id=I-X-ijtoD9QC&pg=PA55 |title=The Languages of Creativity: Models, Problem-solving, Discourse |publisher=University of Delaware Press |year=1986 |isbn=978-0-87413-280-9 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028023637/https://books.google.com/books?id=I-X-ijtoD9QC&pg=PA55#v=onepage&q&f=false |url-status=live }}
* {{cite journal |ref=Astbury |doi=10.1038/1901124a0 |pmid=13684868 |title=Molecular Biology or Ultrastructural Biology ? |journal=Nature |volume=190 |issue=4781 |page=1124 |year=1961 |last1=Astbury |first1=W.T. |bibcode=1961Natur.190.1124A |s2cid=4172248 |doi-access=free }}
* {{cite book |ref=Ben |author=Ben-Menahem, Ari |title=Historical Encyclopedia of Natural and Mathematical Sciences |url=https://books.google.com/books?id=9tUrarQYhKMC&pg=PA2982 |year=2009 |publisher=Springer |isbn=978-3-540-68831-0 |page=2982 |bibcode=2009henm.book.....B }}
* {{cite book |ref = Burton |author = Burton, Feldman |url = https://books.google.com/books?id=xnckeeTICn0C&pg=PA206 |title = The Nobel Prize: A History of Genius, Controversy, and Prestige |publisher = Arcade Publishing |year = 2001 |isbn = 978-1-55970-592-9 }}
* {{cite book |ref=Butler |author=Butler, John M. |title=Fundamentals of Forensic DNA Typing |url=https://books.google.com/books?id=-OZeEmqzE4oC&pg=PA5 |year=2009 |publisher=Academic Press |isbn=978-0-08-096176-7 }}
* {{cite journal |ref=Chandan |doi=10.1089/dna.2006.0567 |pmid=17465885 |title=MiRNA: Licensed to Kill the Messenger |journal=DNA and Cell Biology |volume=26 |issue=4 |pages=193–194 |year=2007 |last1=Sen |first1=Chandan K. |last2=Roy |first2=Sashwati |s2cid=10665411 }}
* {{cite book |ref=Clarence |author=Clarence, Peter Berg |title=The University of Iowa and Biochemistry from Their Beginnings |url=https://books.google.com/books?id=XwQhAQAAIAAJ&pg=PA1 |year=1980 |publisher=University of Iowa |isbn=978-0-87414-014-9 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028023637/https://books.google.com/books?id=XwQhAQAAIAAJ&pg=PA1 |url-status=live }}
* {{Cite journal |ref=Edwards |doi=10.1016/0022-2836(92)91059-x |pmid=1518049 |title=Molecular structure of the B-DNA dodecamer d(CGCAAATTTGCG)2 an examination of propeller twist and minor-groove water structure at 2·2Åresolution |journal=Journal of Molecular Biology |volume=226 |issue=4 |pages=1161–1173 |year=1992 |last1=Edwards |first1=Karen J. |last2=Brown |first2=David G. |last3=Spink |first3=Neil |last4=Skelly |first4=Jane V. |last5=Neidle |first5=Stephen }}
* {{cite book |ref = Eldra |author1 = Eldra P. Solomon |author2 = Linda R. Berg |author3 = Diana W. Martin |title = Biology, 8th Edition, International Student Edition |publisher = Thomson Brooks/Cole |isbn = 978-0-495-31714-2 |url = http://www.slideshare.net/nicolledb05/biology-solomon-berg-martin-8th-edition |year = 2007 |archive-url = https://web.archive.org/web/20160304064412/http://www.slideshare.net/nicolledb05/biology-solomon-berg-martin-8th-edition |archive-date = 2016-03-04 }}
* {{cite journal |ref=Fariselli |doi=10.1093/bib/bbl032 |pmid=17003074 |title=The WWWH of remote homolog detection: The state of the art |journal=Briefings in Bioinformatics |volume=8 |issue=2 |pages=78–87 |year=2006 |last1=Fariselli |first1=P. |last2=Rossi |first2=I. |last3=Capriotti |first3=E. |last4=Casadio |first4=R. |doi-access=free }}
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* {{cite book |ref=Hamblin |author=Hamblin, Jacob Darwin |url=https://books.google.com/books?id=mpiZRAiE0JwC&pg=PA26 |title=Science in the Early Twentieth Century: An Encyclopedia |publisher=ABC-CLIO |year=2005 |isbn=978-1-85109-665-7 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028023638/https://books.google.com/books?id=mpiZRAiE0JwC&pg=PA26 |url-status=live }}
* {{cite book |ref=Helvoort |author=Helvoort, Ton van |url=https://books.google.com/books?id=fjhdAgAAQBAJ&pg=PA81 |title=Reader's Guide to the History of Science |editor=Arne Hessenbruch |publisher=Fitzroy Dearborn Publishing |year=2000 |isbn=978-1-884964-29-9 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024114/https://books.google.com/books?id=fjhdAgAAQBAJ&pg=PA81#v=onepage&q&f=false |url-status=live }}
* {{cite book |ref=Holmes |author=Holmes, Frederic Lawrence |url=https://books.google.com/books?id=MLY-x9a393QC&pg=PR15 |title=Lavoisier and the Chemistry of Life: An Exploration of Scientific Creativity |publisher=University of Wisconsin Press |year=1987 |isbn=978-0-299-09984-8 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024115/https://books.google.com/books?id=MLY-x9a393QC&pg=PR15#v=onepage&q&f=false |url-status=live }}
* {{cite book |ref=Horton |editor=Horton, Derek |url=https://books.google.com/books?id=JQluAAAAQBAJ&pg=PA36 |title=Advances in Carbohydrate Chemistry and Biochemistry, Volume 70 |publisher=Academic Press |year=2013 |isbn=978-0-12-408112-3 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024115/https://books.google.com/books?id=JQluAAAAQBAJ&pg=PA36#v=onepage&q&f=false |url-status=live }}
* {{cite book |ref=Hunter |author=Hunter, Graeme K. |title=Vital Forces: The Discovery of the Molecular Basis of Life |year=2000 |publisher=Academic Press |isbn=978-0-12-361811-5 |url=https://books.google.com/books?id=VdHV5ET4usoC |access-date=2020-06-05 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024115/https://books.google.com/books?id=VdHV5ET4usoC |url-status=live }}
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* {{cite journal |ref=Kauffman |doi=10.1007/s00897010444a |title=Friedrich Wöhler (1800–1882), on the Bicentennial of His Birth |journal=The Chemical Educator |volume=6 |issue=2 |pages=121–133 |year=2001 |last1=Kauffman |first1=George B. |last2=Chooljian |first2=Steven H. |s2cid=93425404 }}
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* {{cite journal |ref=Knowles |doi=10.1146/annurev.bi.49.070180.004305 |pmid=6250450 |title=Enzyme-Catalyzed Phosphoryl Transfer Reactions |journal=Annual Review of Biochemistry |volume=49 |pages=877–919 |year=1980 |last1=Knowles |first1=J.R. |issue=1 |bibcode=1980ARBio..49..877K |s2cid=7452392 }}
* {{cite book |ref=Metzler |author1=Metzler, David Everett |author2=Metzler, Carol M. |title=Biochemistry: The Chemical Reactions of Living Cells |volume=1 |url=https://books.google.com/books?id=1R_a_D6SSJEC&pg=PA58 |year=2001 |publisher=Academic Press |isbn=978-0-12-492540-3 }}
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* {{cite journal |ref=Rojas |doi=10.3390/molecules16032672 |pmid=21441869 |pmc=6259834 |title=Challenges and Perspectives of Chemical Biology, a Successful Multidisciplinary Field of Natural Sciences |journal=Molecules |volume=16 |issue=3 |pages=2672–2687 |year=2011 |last1=Rojas-Ruiz |first1=Fernando A. |last2=Vargas-Méndez |first2=Leonor Y. |last3=Kouznetsov |first3=Vladimir V. |doi-access=free }}
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* {{cite book |ref=Slabaugh |author1=Slabaugh, Michael R. |author2=Seager, Spencer L. |title=Organic and Biochemistry for Today |publisher=Brooks Cole |location=Pacific Grove |year=2013 |isbn=978-1-133-60514-0 |edition=6th |url=https://books.google.com/books?id=K-MBTrn3ZDQC |access-date=2020-06-05 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024617/https://books.google.com/books?id=K-MBTrn3ZDQC |url-status=live }}
* {{cite book |ref=Sherwood |author1=Sherwood, Lauralee |author2=Klandorf, Hillar |author3=Yancey, Paul H. |title=Animal Physiology: From Genes to Organisms |url=https://books.google.com/books?id=I6X8G8YPdv4C&pg=PA558 |year=2012 |publisher=Cengage Learning |isbn=978-0-8400-6865-1 }}
* {{cite book |ref=Stryer |vauthors=Stryer L, Berg JM, Tymoczko JL |title=Biochemistry |publisher=W.H. Freeman |location=San Francisco |edition=6th |year=2007 |isbn=978-0-7167-8724-2 |url=https://archive.org/details/biochemistry0006berg |url-access=registration }}
* {{cite book |ref=Tropp |author=Tropp, Burton E. |title=Molecular Biology |edition=4th |year=2012 |publisher=Jones & Bartlett Learning |isbn=978-1-4496-0091-4 |url=https://books.google.com/books?id=CCQYtlufUIAC |access-date=2020-06-05 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024617/https://books.google.com/books?id=CCQYtlufUIAC |url-status=live }}
* {{cite book |ref=UNICEF |author=UNICEF |title=Facts for life |date=2010 |publisher=United Nations Children's Fund |location=New York |isbn=978-92-806-4466-1 |edition=4th |url=http://www.unicef.org/nutrition/files/Facts_for_Life_EN_010810.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.unicef.org/nutrition/files/Facts_for_Life_EN_010810.pdf |archive-date=2022-10-09 |url-status=live }}
* {{cite journal |ref=Ulveling |doi=10.1016/j.biochi.2010.11.004 |pmid=21111023 |title=When one is better than two: RNA with dual functions |journal=Biochimie |volume=93 |issue=4 |pages=633–644 |year=2011 |last1=Ulveling |first1=Damien |last2=Francastel |first2=Claire |last3=Hubé |first3=Florent |s2cid=22165949 |url=https://hal-univ-diderot.archives-ouvertes.fr/hal-02127323/file/Ulveling%20Review%20revised.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal-univ-diderot.archives-ouvertes.fr/hal-02127323/file/Ulveling%20Review%20revised.pdf |archive-date=2022-10-09 |url-status=live }}
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* {{cite book |ref=Ziesak |author1=Ziesak, Anne-Katrin |author2=Cram Hans-Robert |url=https://books.google.com/books?id=ulN4rKWA8c4C&pg=PA169 |title=Walter de Gruyter Publishers, 1749–1999 |publisher=Walter de Gruyter & Co |year=1999 |isbn=978-3-11-016741-2 |access-date=2015-07-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028024618/https://books.google.com/books?id=ulN4rKWA8c4C&pg=PA169 |url-status=live }}
* {{cite news |last1=Ashcroft |first1=Steve |title=Professor Sir Philip Randle; Researcher into metabolism: [1st Edition] |newspaper=Independent |id={{ProQuest|311080685}} }}
{{refend}}

== Further reading ==
{{refbegin|30em}}
* Fruton, Joseph S.  ''[[iarchive:proteinsenzymesg0000frut|Proteins, Enzymes, Genes: The Interplay of Chemistry and Biology]]''.  Yale University Press: New Haven, 1999.  {{ISBN|0-300-07608-8}}
* Keith Roberts, Martin Raff, Bruce Alberts, Peter Walter, Julian Lewis and Alexander Johnson, ''Molecular Biology of the Cell''
** 4th Edition, Routledge, March, 2002, hardcover, 1616 pp. {{ISBN|0-8153-3218-1}}
** 3rd Edition, Garland, 1994, {{ISBN|0-8153-1620-8}}
** 2nd Edition, Garland, 1989, {{ISBN|0-8240-3695-6}}
* Kohler, Robert.  ''From Medical Chemistry to Biochemistry: The Making of a Biomedical Discipline''. Cambridge University Press, 1982.
* {{cite journal |doi=10.1371/journal.pone.0190046 |pmid=29267345 |pmc=5739466 |title=Wikipedia as a gateway to biomedical research: The relative distribution and use of citations in the English Wikipedia |journal=PLOS ONE |volume=12 |issue=12 |article-number=e0190046 |year=2017 |last1=Maggio |first1=Lauren A. |last2=Willinsky |first2=John M. |last3=Steinberg |first3=Ryan M. |last4=Mietchen |first4=Daniel |last5=Wass |first5=Joseph L. |last6=Dong |first6=Ting |bibcode=2017PLoSO..1290046M |doi-access=free }}
{{refend}}

== External links ==
{{Library resources box}}
{{wikibooks}}
{{commons category|Biochemistry}}
{{WVD}}
* {{cite web |url= http://www.biochemistry.org/ |title = Biochemical Society}}
* [http://biochemweb.fenteany.com/ The Virtual Library of Biochemistry, Molecular Biology and Cell Biology]
* [https://web.archive.org/web/20040220230345/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=stryer.TOC&depth=2 Biochemistry, 5th ed.] Full text of Berg, Tymoczko, and Stryer, courtesy of [[National Center for Biotechnology Information|NCBI]].
* [http://www.systemsX.ch/ SystemsX.ch – The Swiss Initiative in Systems Biology] {{Webarchive|url=https://web.archive.org/web/20170119082115/http://www.systemsx.ch/ |date=2017-01-19 }}
* [http://biochem.science.oregonstate.edu/content/biochemistry-free-and-easy Full text of Biochemistry] by Kevin and Indira, an introductory biochemistry textbook.

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