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Glycogenesis is the process of glycogen synthesis or the process of converting glucose into glycogen in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle , in the liver , and also activated by insulin in response to high glucose levels .
Glycogenolysis takes place in the cells of the muscle and liver tissues in response to hormonal and neural signals. In particular, glycogenolysis plays an important role in the fight-or-flight response and the regulation of glucose levels in the blood.
The regulation of glucose levels through Homeostasis This tight regulation is referred to as glucose homeostasis . Insulin , which lowers blood sugar, and glucagon , which raises it, are the most well known of the hormones involved, but more recent discoveries of other glucoregulatory hormones have expanded the understanding of this process.
Conversely, glycogenesis is enhanced and glycogenolysis inhibited when there are high levels of insulin in the blood. [ 15 ] The level of circulatory glucose (known informally as "blood sugar"), as well as the detection of nutrients in the Duodenum is the most important factor determining the amount of glucagon or insulin produced.
Glycogen synthase (UDP-glucose-glycogen glucosyltransferase) is a key enzyme in glycogenesis, the conversion of glucose into glycogen. It is a glycosyltransferase (EC 2.4.1.11) that catalyses the reaction of UDP-glucose and (1,4-α-D-glucosyl) n to yield UDP and (1,4-α-D-glucosyl) n+1.
Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphorylase is also studied as a model protein regulated by both reversible phosphorylation and allosteric effects.
The ratio of NADPH:NADP + is the primary mode of regulation for the enzyme and is normally about 100:1 in liver cytosol [citation needed]. This makes the cytosol a highly-reducing environment. An NADPH-utilizing pathway forms NADP +, which stimulates Glucose-6-phosphate dehydrogenase to produce more NADPH. This step is also inhibited by acetyl CoA.
Glucose-6-phosphate is the product of glycogenolysis or gluconeogenesis, where the goal is to increase free glucose in the blood due body being in catabolic state. Other cells such as muscle and brain cells do not contain glucose 6-phosphatase.