Editing Metabolic pathway (section)

{{Short description|Linked series of chemical reactions occurring within a cell}}
{{Biochemistry sidebar}}
In [[biochemistry]], a '''metabolic pathway''' is a linked series of [[chemical reaction]]s occurring within a [[cell (biology)|cell]].  The [[reactant]]s, products, and [[Metabolic intermediate|intermediates]] of an [[enzymatic reaction]] are known as [[metabolites]], which are modified by a sequence of chemical reactions [[catalyze]]d by [[enzyme]]s.<ref name="Nelson">{{cite book| vauthors = Nelson DL, Cox MM |title=Lehninger principles of biochemistry|date=2008|publisher=W.H. Freeman|location=New York|isbn=978-0-7167-7108-1|edition=5th|url=https://archive.org/details/lehningerprincip00lehn_1}}</ref>{{rp|26}} In most cases of a metabolic pathway, the [[product (chemistry)|product]] of one enzyme acts as the [[substrate (chemistry)|substrate]] for the next. However, side products are considered waste and removed from the cell.<ref>{{Cite book|title=Biochemistry and molecular biology| vauthors = Alison S, Papachristodoulou DK, Despo K, Elliott WH, Elliott DC |isbn=978-0-19-960949-9 |edition=Fifth|location=Oxford|oclc=862091499|year = 2014}}</ref>

Different metabolic pathways function in the position within a [[Eukaryotic Cell|eukaryotic cell]] and the significance of the pathway in the given compartment of the cell.<ref>{{cite book|title=An Introduction to Metabolic Pathways by S. DAGLEY|date=March 1971|publisher=Sigma Xi, The Scientific Research Society|edition=Vol. 59, No. 2|page=266| vauthors = Nicholson DE }}</ref> For instance, the [[electron transport chain]] and [[oxidative phosphorylation]] all take place in the [[mitochondrial membrane]].<ref name="Harvey">{{cite book| vauthors = Harvey RA |title=Biochemistry|date=2011|publisher=Wolters Kluwer|location=Baltimore, MD |isbn=978-1-60831-412-6|edition=5th}}</ref>{{rp|73, 74 & 109}} In contrast, [[glycolysis]], [[pentose phosphate pathway]], and [[Fatty acid synthesis|fatty acid biosynthesis]] all occur in the [[cytosol]] of a cell.<ref name="Voet, Voet, Pratt">{{cite book| vauthors = Voet D, Voet JD, Pratt CW |title=Fundamentals of Biochemistry: Life at the Molecular Level|date=2013|publisher=Wiley|location=Hoboken, NJ|isbn=978-0470-54784-7|edition=4th|title-link=Fundamentals of Biochemistry: Life at the Molecular Level}}</ref>{{rp|441–442}}

There are two types of metabolic pathways that are characterized by their ability to either synthesize molecules with the utilization of energy ([[Anabolism|anabolic pathway]]), or break down complex molecules and release energy in the process ([[Catabolism|catabolic pathway]]).<ref name="Campbell">{{cite book | vauthors = Reece JB, Campbell NA |title=Campbell Biology |date=2011 |publisher=Benjamin Cummings / Pearson |location=Boston |isbn=978-0-321-55823-7 |edition=9th |pages=[https://archive.org/details/campbellbiologyj00reec/page/143 143] }}</ref>

The two pathways complement each other in that the energy released from one is used up by the other. The degradative process of a catabolic pathway provides the energy required to conduct the [[biosynthesis]] of an anabolic pathway.<ref name="Campbell"/> In addition to the two distinct metabolic pathways is the [[amphibolic]] pathway, which can be either catabolic or anabolic based on the need for or the availability of energy.<ref>{{cite book| vauthors = Berg JM, Tymoczko JL, Stryer L, Gatto GJ |title=Biochemistry|date=2012|publisher=W.H. Freeman|location=New York|isbn=978-1-4292-2936-4 |page=429|edition=7th}}</ref>

Pathways are required for the maintenance of [[homeostasis]] within an [[organism]] and the [[Flux (metabolism)|flux]] of metabolites through a pathway is regulated depending on the needs of the cell and the availability of the substrate. The end product of a pathway may be used immediately, initiate another metabolic pathway or be stored for later use. The [[metabolism]] of a cell consists of an elaborate [[metabolic network|network]] of interconnected pathways that enable the synthesis and breakdown of molecules (anabolism and catabolism).