Metabolisme dan Regulasi Glikogen: Glikogenesis & Glikogenolisis

Summary

This video explains the key processes of glycogen metabolism, focusing on glycogenesis (the formation of glycogen) and glycogenolysis (the breakdown of glycogen). Glycogenesis involves glucose phosphorylation, conversion to UDP-glucose, and its addition to glycogen chains, facilitated by enzymes like glycogen synthase. Glycogenolysis, on the other hand, breaks down glycogen into glucose-1-phosphate through the action of glycogen phosphorylase. The video also covers the regulation of these processes by hormones such as insulin, glucagon, and epinephrine, which control the activation and deactivation of enzymes, thus regulating glucose levels in the body.

Takeaways

• 😀 Glycogen is a primary storage form of carbohydrates in animals and humans, similar to starch in plants, and is highly branched for rapid breakdown and synthesis of glucose.
• 😀 Glycogenesis is the process of synthesizing glycogen from glucose, starting with glucose being converted into glucose-6-phosphate by the enzyme hexokinase.
• 😀 The enzyme phosphoglucomutase converts glucose-6-phosphate into glucose-1-phosphate, which then forms UDP-glucose with the help of UTP.
• 😀 Glycogen synthase is responsible for adding glucose molecules to the growing glycogen chain, forming 1,4-glycosidic bonds.
• 😀 Branching enzyme creates 1,6-glycosidic bonds, introducing branches into the glycogen structure for more efficient glucose storage and release.
• 😀 Glycogenolysis is the breakdown of glycogen into glucose-1-phosphate, starting with the enzyme glycogen phosphorylase, which removes glucose units from the non-reducing ends.
• 😀 The debranching enzyme plays a crucial role in removing branches in glycogenolysis, enabling the continued breakdown of the glycogen chain.
• 😀 The last glucose unit is released as free glucose after the action of glucan transferase, completing the breakdown process.
• 😀 Glycogen metabolism is hormonally regulated, with glucagon and epinephrine activating glycogenolysis and insulin promoting glycogenesis.
• 😀 Glycogen synthase and glycogen phosphorylase are regulated by phosphorylation; glycogen synthase is active when dephosphorylated, while glycogen phosphorylase is active when phosphorylated.

Q & A

What are the two main processes involved in glycogen metabolism?

The two main processes involved in glycogen metabolism are glycogenesis (the formation of glycogen) and glycogenolysis (the breakdown of glycogen).

What is the role of glycogen in cells?

Glycogen acts as a storage form of carbohydrates in animal and human cells, similar to how starch serves this function in plant cells. It provides a readily available source of glucose when needed.

How does glucose become glycogen in glycogenesis?

In glycogenesis, glucose undergoes phosphorylation by the enzyme hexokinase to form glucose-6-phosphate. This is then converted to glucose-1-phosphate and ultimately to UDP-glucose, which is added to the growing glycogen chain through the action of glycogen synthase.

Why is glycogen highly branched, and how does this benefit the cell?

Glycogen's highly branched structure allows for multiple 'ends' where glucose can be quickly released. This increases the speed at which glucose can be mobilized from glycogen when the body needs energy.

What is the role of the enzyme glycogen branching enzyme?

The glycogen branching enzyme is responsible for creating the branches in the glycogen molecule by transferring a segment of the glucose chain to form a new branch, creating additional ends for glucose release.

How is glycogen broken down during glycogenolysis?

During glycogenolysis, the enzyme glycogen phosphorylase adds a phosphate group to the glucose units at the ends of the glycogen chain, releasing glucose-1-phosphate. This process continues until only a small portion of the chain remains, which is then handled by other enzymes.

What happens when glycogen phosphorylase reaches the branch points in glycogen?

When glycogen phosphorylase reaches a branch point, the enzyme **glucan transferase** helps transfer the glucose residues to the main chain. This process allows the breakdown to continue even in branched regions.

What is the difference between the glucose released in glycogenolysis and the glucose released in glycogenesis?

In glycogenolysis, the glucose released is in the form of glucose-1-phosphate, whereas in glycogenesis, glucose is added as UDP-glucose, which then becomes part of the glycogen molecule.

How do hormones regulate glycogen metabolism?

Hormones like glucagon, epinephrine, and insulin regulate glycogen metabolism by activating or inhibiting enzymes involved in glycogenesis and glycogenolysis. For example, glucagon and epinephrine stimulate glycogen breakdown, while insulin promotes glycogen synthesis.

What is the role of protein kinase in glycogen metabolism regulation?

Protein kinase is activated by glucagon and epinephrine and plays a crucial role in glycogen metabolism by phosphorylating enzymes like glycogen synthase (inactivating it) and glycogen phosphorylase (activating it), thus promoting glycogenolysis.

How does insulin affect glycogen metabolism?

Insulin promotes glycogen synthesis by activating protein phosphatase, which dephosphorylates and activates glycogen synthase while deactivating glycogen phosphorylase, thereby reducing glycogen breakdown.