MBBS Stage 1: Glycogen Synthesis and Degradation

Questions and Answers

What is the primary function of liver glycogen?

To maintain constant levels of glucose in the blood (correct)

To act as a fuel source for the liver tissue

To provide a rapid source of glucose for muscle contraction

To regulate the activity of glycogen synthetase

What is the approximate amount of glycogen stored in the liver?

100-120g (correct)

150-180g

300-350g

200-250g

What is the primary function of muscle glycogen?

To provide a rapid source of glucose for muscle contraction (correct)

To act as a fuel source for the liver tissue

To regulate the activity of glycogen phosphorylase

To maintain constant levels of glucose in the blood

What is the approximate amount of glycogen stored in the muscle?

250-300g Signup and view all the answers

What is the key enzyme responsible for the conversion of glucose to glycogen?

Glycogen synthetase Signup and view all the answers

What is the characteristic structure of glycogen?

Branched structure Signup and view all the answers

What type of linkages are present in glycogen?

α-1,4 and α-1,6 Signup and view all the answers

What is the role of ATP or UTP or GTP in biosynthetic pathways?

To drive the reactions forward Signup and view all the answers

What is the characteristic of the enzyme reactions at the beginning or end of a biosynthetic pathway?

They are tightly regulated Signup and view all the answers

What is the product of the reaction between glucose-1-P and UTP?

UDP glucose Signup and view all the answers

What is the role of glycogen synthase in glycogen synthesis?

It extends the straight chains Signup and view all the answers

What is the approximate number of units introduced by the branching enzyme?

8-10 Signup and view all the answers

What is the site of action of the branching enzyme?

Site of new chain formation Signup and view all the answers

What is the role of glycogenin in glycogen synthesis?

It acts as a primer Signup and view all the answers

What is the product of glycogen breakdown by phosphorylase?

Glucose-1-phosphate Signup and view all the answers

What is the function of the debranching enzyme in glycogen breakdown?

To remove glucose units from branched regions Signup and view all the answers

What is the effect of adrenaline on glycogen phosphorylase?

It activates the enzyme Signup and view all the answers

What is the role of calcium ions in muscle glycogen breakdown?

They activate glycogen phosphorylase kinase Signup and view all the answers

What is the effect of high glucose levels on liver glycogen phosphorylase?

It inhibits the enzyme Signup and view all the answers

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

It inhibits glycogen synthase Signup and view all the answers

What is the effect of AMP on glycogen phosphorylase?

It activates the enzyme Signup and view all the answers

What is the site of action of glycogen phosphorylase?

1,4 glycoside links Signup and view all the answers

Study Notes

Glycogen Synthesis and Regulation

Glycogen is a branched polymer with α-1,4 and α-1,6 glycoside links.
The liver stores 100-120g of glycogen, while muscles store 250-300g.
Liver glycogen is sensitive to blood glucose concentration and regulates it under insulin and glucagon control.
Muscle glycogen is sensitive to energy needs and responds to adrenaline, calcium, AMP, and ATP.

Structure of Glycogen

Glycogen has a branched structure, with α-1,6 links at the terminal residues.
The branched structure is important for its physiological function.

Biosynthetic Pathways

ATP, UTP, or GTP are needed as cofactors to drive reactions forward.
One or more enzyme reactions are irreversible, and alternative enzymes are used for the opposite direction.
Enzyme reactions at the beginning or end of the pathway are tightly regulated.

Glycogen Synthesis from Glucose

Glucose-1-P is converted to UDP-glucose in the presence of UTP and pyrophosphatase.
UDP-glucose is then added to a protein primer (glycogenin) by glycogen synthase.
Glycogen synthase and branching enzyme produce the branched structure of glycogen.

Regulation of Glycogen Synthesis

Glycogen synthase is regulated by phosphorylation, which inactivates the enzyme.
Regulation of glycogen synthase is controlled by protein kinase and protein phosphatase.

Glycogen Breakdown

Glycogen breakdown is initiated by glycogen phosphorylase, which removes glucose units from branched regions.
The breakdown of straight chain regions requires glycogen phosphorylase acting on 1,4 links.
Release of free glucose occurs through the production of glucose-1-phosphate, which is then converted to glucose-6-phosphate.

Regulation of Glycogen Phosphorylase

Glycogen phosphorylase is regulated by protein kinase and protein phosphatase.
Additional controls: liver responds to insulin/glucagon, and muscle responds to adrenaline, calcium, AMP, and ATP.

Additional Controls

In the liver, insulin inactivates glycogen phosphorylase, while glucagon activates it.
In muscle, calcium ions released during contraction bind to calmodulin, activating glycogen phosphorylase kinase, which in turn activates phosphorylase.
In prolonged exercise, AMP is an allosteric activator of glycogen phosphorylase.

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Description

This quiz covers the synthesis and regulation of glycogen, its importance in maintaining blood glucose levels, and its relevance to nutrition and metabolism. It is suitable for MBBS students in their first stage.