Glycogenesis: How to Synthesize Glycogen?

Glycogenesis is the metabolic pathway in which glucose (a simple sugar) is converted into glycogen, which stores energy in muscle cells. Glycogen is also found in the liver and brain tissue. The body uses glycogen whenever it has enough energy stored from food or exercise.

Glycogen is a carbohydrate that is formed from glucose during periods of high metabolism. To store glycogen, the body breaks down protein into amino acids, which then combine with glucose to form glycogen.
Glycogen storage is regulated by insulin, which increases after a meal and decreases after exercise.

Insulin causes the liver to release fatty acids, which are then broken down into ketones. Ketones are released into the bloodstream through the kidneys and muscles. When blood levels of ketones rise, they signal the brain to stop storing fat. This helps burn fat instead of carbohydrates.

“The Synthesis of Glycogen from Glucose is called Glycogenesis.” It takes place in the cytosol and requires ATP and UTP, besides glucose. ”

The goal of glycolysis, glycogenolysis, and the citric acid cycle is to conserve energy as ATP from the catabolism of carbohydrates.

Glycogenesis

If the cells have sufficient supplies of ATP, then these pathways and cycles are inhibited.

Under these conditions of excess ATP, the liver will attempt to convert a variety of excess molecules into glucose and/or glycogen.

What is the function of glycogenesis?

The function of glycogenesis is to synthesize glucose from other nutrients in the body. The process of glycogenesis is the reverse of gluconeogenesis which synthesizes glucose from other amino acids.

In addition to generating energy for normal metabolism, this also allows certain cells and organelles in our body to store large amounts of glucose that can be used during periods where fat cannot supply enough fuel.

What happens during glycogenesis?

Glycogenesis is the process by which glucose is produced from glycogen. Glycogen is a storage form of glucose that is found in the liver and muscle cells.

When the body needs energy, glycogen is broken down into glucose and water. Glucose is used by the body to provide fuel for activities like muscle contraction or nerve impulse transmission.

What is the function of glycogenesis?

The function of glycogenesis is to synthesize glucose from other nutrients in the body. The process of glycogenesis is the reverse of gluconeogenesis which synthesizes glucose from other amino acids.

In addition to generating energy for normal metabolism, this also allows certain cells and organelles in our body to store large amounts of glucose that can be used during periods where fat cannot supply enough fuel.

What are the steps of glycogenolysis?


There are six major steps that are involved in Glycogenolysis:

Glycogenesis mechanism

What are the key enzymes of glycogenesis?

The key enzymes of glycogenesis are Hexokinase, Pyruvate Kinase, and Phosphofructokinase.

Step 1: Glucose Phosphorylation

Glucose is phosphorylated into Glucose-6-Phosphate, a reaction that is common to the first reaction in the pathway of glycolysis from Glucose.

This reaction is catalyzed by Hexokinase in Muscle and Glucokinase in the Liver.

Glucose + ATP –> Glucose-6-P 

(Enzyme: Glucokinase or Hexokinase)


Step 2: Glc-6-P to Glc-1-P conversion

Glucose-6-P is converted to Glc-1-Phosphate in a reaction catalyzed by the enzyme “Phosphoglucomutase”.

Glucose-6-P + Enz-P      <—>     Glucose-1,6-bis Phosphate + Enz    <—>      Glucose-1-Phosphate + Enzyme-P

(Enzyme: Phosphoglucomutase)


Step 3: Attachment of UTP to Glc-1-P

Glucose-1-P reacts with Uridine triphosphate (UTP) to form the active nucleotide Uridine diphosphate Glucose (UDP-Glc). The reaction is catalyzed by the enzyme “UDPGlc Pyrophosphorylase”.

UTP + Glucose-1-P  <—> UDPGlc + PPi

(Enzyme: UDPGlc Pyrophosphorylase)

Glycogenesis mechanism

Step 4: Attachment of UDP-Glc to Glycogen Primer

A small fragment of pre-existing glycogen must act as a “Primer” (also called GLYCOGENIN) to initiate glycogen synthesis. The Glycogenin can accept glucose from UDP-Glc.

The hydroxyl group of the amino acid tyrosine of Glycogenin is the site at which the initial glucose unit is attached. The enzyme Glycogen initiator synthase transfers the first molecule of glucose to Glycogenin.

Then glycogenin itself takes up glucose residues to form a fragment of primer which serves as an acceptor for the rest of the glucose molecules.

glycogen primer

Step 5: Glycogen synthesis by Glycogen synthase

Glycogen synthase, the enzyme transfers the Glucose from UDP-Glc to the non-reducing end of Glycogen to form alpha 1,4-linkages.

Glycogen synthase catalyzes the synthesis of a linear unbranched molecule with alpha-1,4-glycosidic linkages.


Step 6: Glycogen Branches formation

In this step, the formation of branches is brought about by the action of a branching enzyme, namely branching enzyme (amylo-[1—>4]—>[1—>6]-transglucosidase).

This enzyme transfers a small fragment of five to eight glucose residues from the non-reducing end of the glycogen chain. to another glucose residue where it is linked by the alpha-1,6 bond.

It leads to the formation of a new non-reducing end, besides the existing one. The glycogen chain will be elongated and branched.

The overall reaction of Glycogenesis,

(Glucose)n  +  Glucose   + 2 ATP  –> (Glucose) n+1  + 2 ADP   + Pi

Two ATP molecules will be utilized in this process. One is required for the phosphorylation of Glucose and the other is needed for the conversion of UDP to UTP.

How does glycogenesis regulate tissue glucose consumption and blood sugar levels?

When the amount of stored forms of starch reaches a certain point, it begins being degraded into its components: glucose and water. The breakdown is controlled by both enzymes that break down the existing chains (glycogenolysis) and new cells that are not programmed to use nutrients just yet, thus becoming “flexible enough” to break down the new chains (glycogen synthesis). Hence, this acts as a feedback mechanism to maintain stable tissue glucose levels.

The amount of glycogen accumulated in excess is stored in muscles and the liver in the part of their supplies for energy conversion/respiration when needed throughout life, but not all cells can produce enough reserves upfront to continuously support such intense use.

The mechanism by which it persists long enough to develop into a muscle cell is not well known. One interesting hypothesis is that the glycogen storage cells in muscles may contain an enzyme called alpha-1,6-glycosidase (previously named glucoamylase), while other types of cells, like nerves, do with another type: beta 1,3/4 or starch-14 glucose aminohydrolases.

What are the benefits of increasing glycogen stores?

There are many benefits to increasing glycogen stores. Glycogen is a form of energy storage that can be used by the body during exercise. When glycogen stores are increased, the body has more energy available to it, which can help to improve performance.

Additionally, increasing glycogen stores can help to delay fatigue, as glycogen is broken down during exercise to provide energy. This can allow for longer and more intense workouts. Finally, increasing glycogen stores can help to improve recovery after exercise, as glycogen is used to replenish energy stores in the muscles.

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