A Futile cycle is when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than wasting energy. In Biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. [1] For example, if glycolysis and gluconeogenesis were to be active at the same time, glucose would be converted to pyruvate by glycolysis and then converted back to glucose by gluconeogenesis, with an overall consumption of ATP. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy [2] Futile cycles may have a role in metabolic regulation, where a futile cycle would be a system oscillating between two states and very sensitive to small changes in the activity of any of the enzymes involved. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins [3] The cycle does generate heat, and may be used to maintain homeostasis. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit
Glycolysis/Gluconeogenesis
This futile cycle is
example of futile cycle:
During glycolysis fructose-6-phosphate is converted to fructose-1,6-bisphosphate by the help of the enzyme phosphofructokinase(PFK).
ATP+fructose-6-phosphate---------->fructose-1,6-bisphosphate+ADP --------------(1)
But during gluconeogenesis(i. e. synthesis of glucose from pyruvate and other compounds) the revese reaction takes place being catalyzed by fructose-1,6-bisphosphatase(FBPase-1).
fructose-1,6-bisphosphate+H2O---------->fructose-6-phosphate+Pi --------------(2)
the sum total of the two above reaction is-
ATP+H2O------>ADP+Pi+Heat
that is, hydrolysis of ATP without any useful metabolic work being done. Clearly, if these two reactions were allowed to proceed simultaneously at a high rate in the same cell, a large amount of chemical energy would be dissipated as heat. This uneconomical process has been called a futile cycle.
References
- ^ Schwender J, Ohlrogge J, Shachar-Hill Y (2004). "Understanding flux in plant metabolic networks". Curr Opin Plant Biol 7 (3): 309–17. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15134752.
- ^ Boiteux A, Hess B (1981). "Design of glycolysis". Philos Trans R Soc Lond B Biol Sci 293 (1063): 5–22. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 6115423.
- ^ Samoilov M, Plyasunov S, Arkin A (2005). "Stochastic amplification and signaling in enzymatic futile cycles through noise-induced bistability with oscillations". Proc Natl Acad Sci U S A 102 (7): 2310–5. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15701703.
Lehninger Principles of Biochemistry (Nelson, W[1]. H. , Freeman, 4th Ed, 2004)
External links
Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and booksDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic