Phosphorylation
In biochemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion.[1] This process and its inverse, dephosphorylation, are common in biology.[2] Protein phosphorylation often activates (or deactivates) many enzymes.[3][4]
During respiration and photosynthesis
Phosphorylation is essential to the processes of both
Phosphorylation of glucose
Glucose metabolism
Phosphorylation of sugars is often the first stage in their catabolism. Phosphorylation allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter. Phosphorylation of glucose is a key reaction in sugar metabolism. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by:
- D-glucose + ATP → D-glucose 6-phosphate+ ADP
- ΔG° = −16.7 kJ/mol (° indicates measurement at standard condition)
Glycolysis
Glycolysis is an essential process of glucose degrading into two molecules of pyruvate, through various steps, with the help of different enzymes. It occurs in ten steps and proves that phosphorylation is a much required and necessary step to attain the end products. Phosphorylation initiates the reaction in step 1 of the preparatory step[5] (first half of glycolysis), and initiates step 6 of payoff phase (second phase of glycolysis).[6]
Glucose, by nature, is a small molecule with the ability to diffuse in and out of the cell. By phosphorylating glucose (adding a phosphoryl group in order to create a negatively charged phosphate group[7]), glucose is converted to glucose-6-phosphate, which is trapped within the cell as the cell membrane is negatively charged. This reaction occurs due to the enzyme hexokinase, an enzyme that helps phosphorylate many six-membered ring structures. Phosphorylation takes place in step 3, where fructose-6-phosphate is converted to fructose 1,6-bisphosphate. This reaction is catalyzed by phosphofructokinase.
While phosphorylation is performed by ATPs during preparatory steps, phosphorylation during payoff phase is maintained by inorganic phosphate. Each molecule of
Phosphorylation functions is an extremely vital component of glycolysis, as it helps in transport, control, and efficiency.[8]
Glycogen synthesis
High blood glucose releases insulin, stimulating the translocation of specific glucose transporters to the cell membrane; glucose is phosphorylated to glucose 6-phosphate during transport across the membrane by ATP-D-glucose 6-phosphotransferase and non-specific hexokinase (ATP-D-hexose 6-phosphotransferase).[9][10] Liver cells are freely permeable to glucose, and the initial rate of phosphorylation of glucose is the rate-limiting step in glucose metabolism by the liver.[9]
The liver's crucial role in controlling blood sugar concentrations by breaking down glucose into carbon dioxide and glycogen is characterized by the negative
The phosphorylation of glucose can be enhanced by the binding of fructose 6-phosphate (F6P), and lessened by the binding fructose 1-phosphate (F1P). Fructose consumed in the diet is converted to F1P in the liver. This negates the action of F6P on glucokinase,[11] which ultimately favors the forward reaction. The capacity of liver cells to phosphorylate fructose exceeds capacity to metabolize fructose-1-phosphate. Consuming excess fructose ultimately results in an imbalance in liver metabolism, which indirectly exhausts the liver cell's supply of ATP.[12]
Other processes
Phosphorylation of glucose is imperative in processes within the body. For example, phosphorylating glucose is necessary for insulin-dependent
Protein phosphorylation
The prominent role of protein phosphorylation in biochemistry is illustrated by the huge body of studies published on the subject (as of March 2015, the MEDLINE database returns over 240,000 articles, mostly on protein phosphorylation).
See also
References
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- S2CID 253448972. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
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- ^ Chapter 14: Glycolysis and the Catabolism of Hexoses. Archived from the original on 2021-10-17. Retrieved 2016-05-14.
- ^ Garrett R (1995). Biochemistry. Saunders College.
- ^ "Hexokinase - Reaction". www.chem.uwec.edu. Archived from the original on 2020-12-02. Retrieved 2020-07-29.
- ^ Maber J. "Introduction to Glycolysis". Archived from the original on 6 April 2017. Retrieved 18 November 2017.
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- ^ "Regulation of Glycolysis". cmgm.stanford.edu. Archived from the original on 2009-03-03. Retrieved 2017-11-18.
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