Editing Metabolic pathway (section)

==Overview==
[[File:Net reactions for glycolysis of glucose, oxidative decarboxylation of pyruvate, and Krebs cycle..png|alt=Glycolysis, Oxidative Decarboxylation of Pyruvate, and Tricarboxylic Acid (TCA) Cycle|thumb|Net reactions of common metabolic pathways|650x650px]]

Each metabolic pathway consists of a series of biochemical reactions that are connected by their intermediates: the products of one reaction are the [[Substrate (biochemistry)|substrates]] for subsequent reactions, and so on. Metabolic pathways are often considered to flow in one direction. Although all chemical reactions are technically [[Reversible Michaelis–Menten kinetics|reversible]], conditions in the cell are often such that it is [[thermodynamics|thermodynamically]] more favorable for [[flux]] to proceed in one direction of a reaction.<ref>{{Cite journal| vauthors = Cornish-Bowden A, Cárdenas M |author-link1=Athel Cornish-Bowden|date=2000|title=Irreversible reactions in metabolic simulations: how reversible is irreversible?|url=http://academic.sun.ac.za/natural/biochem/btk/book/cornish-bowden.pdf|journal=Animating the Cellular Map|pages=65–71}}</ref> For example, one pathway may be responsible for the synthesis of a particular amino acid, but the breakdown of that amino acid may occur via a separate and distinct pathway. One example of an exception to this "rule" is the metabolism of [[glucose]]. [[Glycolysis]] results in the breakdown of glucose, but several reactions in the glycolysis pathway are reversible and participate in the re-synthesis of glucose ([[gluconeogenesis]]).<ref>{{Cite web |date=2024-06-25 |title=Metabolism - Pathways, Enzymes, Reactions {{!}} Britannica |url=https://www.britannica.com/science/metabolism/The-study-of-metabolic-pathways |access-date=2024-06-28 |website=www.britannica.com |language=en}}</ref>
* [[Glycolysis]] was the first metabolic pathway discovered:
# As [[glucose]] enters a cell, it is immediately [[phosphorylated]] by [[Adenosine triphosphate|ATP]] to [[glucose 6-phosphate]] in the irreversible first step.
# In times of excess [[lipid]] or [[protein]] energy sources, certain reactions in the [[glycolysis]] pathway may run in reverse to produce [[glucose 6-phosphate]], which is then used for storage as [[glycogen]] or [[starch]].
* Metabolic pathways are often [[Control theory|regulated]] by [[feedback inhibition]].
* Some metabolic pathways flow in a 'cycle' wherein each component of the cycle is a substrate for the subsequent reaction in the cycle, such as in the [[Krebs Cycle]] (see below).
* [[Anabolism|Anabolic]] and [[catabolic]] pathways in [[eukaryotes]] often occur independently of each other, separated either physically by compartmentalization within [[organelles]] or separated biochemically by the requirement of different enzymes and co-factors.