MBBS Nutrition: Glycogen Synthesis and Degradation

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Questions and Answers

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

100-120g (correct)

300-350g

200-250g

50-60g

What is the primary function of glycogen in muscle cells?

To maintain blood glucose levels

To store excess glucose for liver metabolism

To provide energy for muscle contraction (correct)

To regulate insulin and glucagon secretion

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

Glycogen synthetase (correct)

Insulin

Glycogen phosphorylase

Glucagon

What is the significance of glycogen's branched structure?

It allows for more efficient storage of glucose Signup and view all the answers

What is the primary hormone responsible for regulating glycogen synthesis in the liver?

Insulin Signup and view all the answers

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

250-300g Signup and view all the answers

What is the result of glycogen breakdown by phosphorylase?

Production of glucose-1-phosphate Signup and view all the answers

What is the role of calcium ions in glycogen phosphorylase activation?

Bind to calmodulin domain of glycogen phosphorylase kinase and activate the enzyme Signup and view all the answers

What is the effect of insulin on glycogen phosphorylase?

Inhibit glycogen phosphorylase Signup and view all the answers

What is the function of debranching enzyme in glycogen breakdown?

Hydrolyze 1,6 glycosidic bonds Signup and view all the answers

What is the effect of adrenaline on glycogen phosphorylase?

Activate glycogen phosphorylase Signup and view all the answers

What is the role of AMP in glycogen phosphorylase activation?

Activate glycogen phosphorylase Signup and view all the answers

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

Inhibit glycogen synthase Signup and view all the answers

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

Inhibit glycogen phosphorylase Signup and view all the answers

What type of linkages are present in glycogen?

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

What is the function of UDP glucose in glycogen synthesis?

It donates glucose units to the growing glycogen chain Signup and view all the answers

What is the role of glycogenin in glycogen synthesis?

It is the protein primer for glycogen synthesis Signup and view all the answers

What is the net result of the action of branching enzyme?

It introduces branch points in glycogen Signup and view all the answers

What is the function of ATP/UTP/GTP in glycogen synthesis?

They are the energy source for glycogen synthesis Signup and view all the answers

What is the role of the reducing end of glycogen?

It is the site of glycogen breakdown Signup and view all the answers

What type of reaction is the formation of UDP glucose?

Transferase reaction Signup and view all the answers

What is the purpose of tightly regulated enzyme reactions in glycogen synthesis?

To allow for alternative enzymes to be used in the opposite direction Signup and view all the answers

Study Notes

Glycogen Synthesis and Degradation

Glycogen is a branched polysaccharide with α-1,6 and α-1,4 glycosidic links, and its structure has physiological significance.
The liver contains 100-120g of glycogen, which is sensitive to blood glucose concentration and plays a crucial role in maintaining constant levels of glucose in the blood.
Muscle contains 250-300g of glycogen, which is sensitive to energy needs and is used as a rapid source of glucose for muscle contraction.

Features of Biosynthetic Pathways

ATP, UTP, or GTP are required 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

Glycogen synthesis involves the conversion of glucose to glycogen, with glycogen synthetase as the key enzyme.
The first stage of glycogen synthesis involves the formation of UDP glucose from glucose-1-P and UTP.
UDP glucose is then added to a protein primer, glycogenin, to form a glycogen chain.
Glycogen synthase and branching enzyme work together to produce the branched structure of glycogen.

Regulation of Glycogen Synthesis

Glycogen synthase is regulated by phosphorylation, which inactivates the enzyme.
Protein kinase and protein phosphatase play a crucial role in the regulation of glycogen synthase.

Glycogen Breakdown

Glycogen breakdown involves the conversion of glycogen to glucose, with glycogen phosphorylase as the key enzyme.
Glycogen phosphorylase breaks down glycogen into glucose-1-phosphate, which is then converted to glucose-6-phosphate.
Glucose-6-phosphate is then converted to glucose in the liver.

Regulation of Glycogen Breakdown

Glycogen phosphorylase is regulated by phosphorylation, which activates the enzyme.
Protein kinase and protein phosphatase play a crucial role in the regulation of glycogen phosphorylase.
Additional controls include insulin and glucagon, which regulate glycogen phosphorylase in the liver, and adrenaline, calcium, and AMP, which regulate glycogen phosphorylase in muscle.

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Description

Assess your knowledge of glycogen synthesis and degradation, including its structure, importance in maintaining blood glucose levels, and regulation. Ideal for MBBS Stage one students.