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, 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.