Editing Enzyme (section)

===Metabolism===

[[Image:Glycolysis metabolic pathway.svg|thumb|upright=2|alt=Schematic diagram of the glycolytic metabolic pathway starting with glucose and ending with pyruvate via several intermediate chemicals. Each step in the pathway is catalyzed by a unique enzyme.|The [[metabolic pathway]] of [[glycolysis]] releases energy by converting [[glucose]] to [[pyruvate]] via a series of intermediate metabolites. Each chemical modification (red box) is performed by a different enzyme.]]

Several enzymes can work together in a specific order, creating [[metabolic pathway]]s.<ref name = "Stryer_2002" />{{rp|30.1}} In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. Sometimes more than one enzyme can catalyze the same reaction in parallel; this can allow more complex regulation: with, for example, a low constant activity provided by one enzyme but an inducible high activity from a second enzyme.<ref name="Rouzer_2009">{{cite journal | vauthors = Rouzer CA, Marnett LJ | title = Cyclooxygenases: structural and functional insights | journal = Journal of Lipid Research | volume = 50 | issue = Suppl | pages = S29–S34 | date = April 2009 | pmid = 18952571 | pmc = 2674713 | doi = 10.1194/jlr.R800042-JLR200  |doi-access=free }}</ref>

Enzymes determine what steps occur in these pathways. Without enzymes, metabolism would neither progress through the same steps and could not be regulated to serve the needs of the cell. Most central metabolic pathways are regulated at a few key steps, typically through enzymes whose activity involves the hydrolysis of ATP. Because this reaction releases so much energy, other reactions that are [[endothermic|thermodynamically unfavorable]] can be coupled to ATP hydrolysis, driving the overall series of linked metabolic reactions.<ref name = "Stryer_2002" />{{rp|30.1}}