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Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage.
Glycogenesis occurs in liver and muscle cells when glucose and ATP are present in relatively high amounts to store glucose molecules by adding simultaneously together to form glycogen molecules. 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, for example after a carbohydrate-containing meal.
This process is energetically unfavorable without free energy input. This pathway is activated by insulin when the body senses high glucose levels normally after a carbohydrate-rich diet.&nbsp;
<h2 style="text-align: justify;">1. Steps of Glycogenesis -</h2>
<h3>1.1 Activation of glucose Monomers :</h3>
Glucose is converted into glucose-6-phosphate by the action of glucokinase or hexokinase, Glucose-6-phosphate is converted into glucose-1-phosphate by the action of Phosphoglucomutase. Now the uridine triphosphate binds with Glucose&ndash;1&ndash;Phosphate and forms the uridine diphosphate glucose which is an activated compound that can donate its glucosyl unit to extending glycogen chain.&nbsp;
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<h3>1.2 Primer formation and Extension of Glycogen Chain :</h3>
Primers for the glycogen synthesis are formed by glycogen in which acts as glucosyltransferase and has Tyr at its active site. It forms 7 residue long residues and then further reaction is carried out by glycogen synthase.
Glycogen synthase is the enzyme that transfers the glucosyl residue from the UDPG to the non-reducing end of the growing chain of glycogen and forms a 1-4 glycogen bond.&nbsp;
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The free UDP is replenished to the UTP for activation of the next glucosyl residue is done by the nucleoside diphosphate kinase. This enzyme is able to catalyze a reversible reaction which equals the utilization of UTP and ATP in the cell.&nbsp;
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Glycogen synthase is inhibited by the 1, 5-gluconolactone, which mimics the oxonium ion&rsquo;s half-chair geometry. It also inhibits glycogen phosphorylase and lysozyme.&nbsp;
<h3 style="text-align: justify;">1.3 Branching of glycogen :</h3>
Glycogen synthase is not able to form branches it forms only near chains so another enzyme is called a branching enzyme. This creates 1-6 bonds by transferring seven residue segments. Every branch point at least four residues away from another branch point. Glycogen is formed with several no reducing ends and one reducing end.&nbsp;
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://vediphlie-aws.s3.ap-south-1.amazonaws.com/Steps_of_Glycogenesis_be29c540fb.PNG" alt="Steps of Glycogenesis" />
Fig.: Steps of Glycogenesis
<h3 style="text-align: left;">1.4 Glycogen Synthase :</h3>
Glycogen Synthase is a typical allosteric enzyme. It is composed of four identical subunits (multiple subunits). The enzyme exists in two conformations named R and T. These conformations are in equilibrium R &harr; T. The substrates bind when the enzyme is in the R state. ATP, ADP, and Pi are allosterically inhibitor Glycogen synthase and bind to the T state and stabilize it shifting the equilibrium to the right.
Glucose-6-phosphate is an allosteric activator of glycogen synthase and binds to the R state and stabilizes it shifting the equilibrium to the left. Glycogen phosphorylase is activated by phosphorylation, whereas glycogen synthase is inhibited. Glycogen phosphorylase is converted from its less active "b" form to an active "a" form by the enzyme phosphorylase kinase. This latter enzyme is itself activated by protein kinase A and deactivated by phosphoprotein phosphatase-1. Like glycogen phosphorylase, allosteric controls are overridden by reversible covalent phosphorylation. In this case the phosphorylated glycogen synthesis, form b is less active than the original dephosphorylated form a. The phosphorylase kinase phosphorylates glycogen synthase. The phosphorylation is reversible. The dephosphorylation is carried out by the enzyme called phosphoprotein phosphatase 1.
Protein kinase A itself is activated by the hormone adrenaline. Epinephrine binds to a receptor protein that activates adenylate cyclase. The latter enzyme causes the formation of cyclic AMP from ATP; two molecules of cyclic AMP bind to the regulatory subunit of protein kinase A, which activates it allowing the catalytic subunit of protein kinase A to dissociate from the assembly and to phosphorylate other proteins.&nbsp;
Returning to glycogen phosphorylase, the less active "b" form can itself be activated without the conformational change. 5'AMP acts as an allosteric activator, whereas ATP is an inhibitor, as already seen with phosphofructokinase control, helping to change the rate of flux in response to energy demand.&nbsp;
Epinephrine not only activates glycogen phosphorylase but also inhibits glycogen synthase. This amplifies the effect of activating glycogen phosphorylase. This inhibition is achieved by a similar mechanism, as protein kinase A acts to phosphorylate the enzyme, which lowers activity. This is known as co-ordinate reciprocal control. &nbsp;
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://vediphlie-aws.s3.ap-south-1.amazonaws.com/Hereditary_Glycogen_Storage_Diseases_bf940dafcc.PNG" alt=" Hereditary Glycogen Storage Diseases" />
<h3>1.5 Glycogen storage disorders :</h3>
(1) Von Gierke&rsquo;s Disease &ndash; 
- Clinical manifestations are fatty liver -&gt; distended abdomen
- Many different kinds depending on the mutated enzyme
This disease is caused by a mutation in G-6-Pase.
This disease is characterized by normal glycogen levels but high levels of trapped phospho-sugars in the form of glucose 6 phosphates.
(2) McArdle&rsquo;s disease -
This is because of mutation in phosphorylase kinase in muscle however the isoenzyme present in the liver is normal. ATP availability is decreased resulted in damage of muscle.
(3) Pompe's Disease -
&ndash; caused due to a mutation in the glucosidase enzyme which is usually found in lysosomes.
&ndash; Leads to large increases in glycogen found in lysosomes in nearly every tissue in the body. Once the glycogen particles are in the lysosome they can no longer function normally. and death occurs at an early age from heart failure.&nbsp;

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Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage.

Glycogenesis - Branching of Glycogen, Glycogen Storage Disorders

Glycogenesis occurs in liver and muscle cells when glucose and ATP are present in relatively high amounts to store glucose molecules by adding simultaneously together to form glycogen molecules. Explore more details here!

Glycogenesis

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