User:Samia fayal/Glycogen

Glycogen, or glycogen (glycogen), is a multi-unit polymer. Glucose is the basic building block in this molecule that acts as an energy store in animals and fungi. [1] [2] [3] Each unit of glucose is linked to the next by an A linkage (4,1), while the branches consist of links (6,1). When blood glucose is low, the process of breaking down glycogen into its main component, glucose, begins. Whereas, the reverse process of converting glucose molecules into glycogen occurs when the level of glucose in the blood rises. Insulin is the hormone responsible for creating glycogen in the human body, while the liver and muscles are the two organs responsible for storing it.

Glycogenesis
It is a manufacturing process that takes place inside cells in which glycogen is built from glucose.

whereabouts

The main site for this process is the cytosol of the liver and muscle cells. Liver cells make up 8-10% of the weight of glycogen formed, and muscles make up 1-2% of its weight. As for the rest of the other cells, they manufacture minute and small amounts of glycogen.

Steps of glycogenogenesis
The process of glycogenesis of uridine glucose diphosphate (UDPG) begins with the presence of 2 enzymes:

1- Glycogen Synthase: This enzyme is the primary enzyme in the synthesis of glycogen. Where it stimulates the transfer of glucose units from uridine glucose diphosphate to what is called a glycogen primer, and thus leads to the attachment of the first carbon atom of the transferred glucose to the fourth carbon atom of the last glucose in the primary glycogen chain and linked by its "alpha-4.1 glycoside link ". This process can be repeated more than once, leading to elongation of the primary glycogen until it reaches a minimum of 11 glucose units, and the chain is called the immature glycogen chain, and then comes the role of the branched enzyme.

2- Branching enzyme: This enzyme carries out the transfer of part of the immature glycogen chain (the transported part consists of a minimum consisting of 6 glucose units) to link it to the nearest chain with an "alpha-6.1 glycosidic link" to form another branching point. It serves as a starting point for replication of the glycogen-synthesized enzyme.

And so the glycogen synthesis process continues

Regulating glycogenesis
This is done in several ways, including:

1- Modification of the covalent bond by hormones: The glycogen synthase exists in two forms, the first being active (in the form of alpha), which is called the insulin effect. Or in an inactive form (in the form of beta), which is called the effect of glucagon on the liver and the effect of adrenaline on the liver and muscles.

2- Dissociation regulation: This is done either by glycogen itself or by glucose hexophosphate.

Significance of glycogen
1- Liver glycogen: It acts as a reserve of glucose that helps maintain blood sugar, especially between meals, and after 12-18 hours of food abstinence, the liver glycogen is depleted and exhausted.

2- Muscle glycogen: It acts as a fuel reserve for the manufacture of adenosine triphosphate (ATP) within the same muscle, especially during contraction, and this glycogen is depleted after prolonged muscle exercise.