Glycogenesis And Glycogenolysis

Question 1

What is the composition of glycogen?

Answer 1

Homopolysaccharide of branched α-D glucose units

Glycogen is primarily made up of glucose molecules linked together in a branched structure.

Question 2

What type of linkages are found in glycogen?

Answer 2

• α-1,4 glycosidic bonds (main chain)
• α-1,6 glycosidic bonds (branch points)

These linkages are crucial for the structure and function of glycogen.

Question 3

Where is glycogen located in the body?

Answer 3

Cytosol of liver and muscle cells

Glycogen is stored in these areas for energy mobilization.

Question 4

Define glycogenesis.

Answer 4

Formation of glycogen from glucose

Glycogenesis is the process through which glucose is converted into glycogen for storage.

Question 5

What substrates are used in glycogenesis in the liver?

Answer 5

• Blood glucose
• Hexoses (fructose, galactose)
• Gluconeogenic precursors (e.g., glycerol, lactate)

These substrates provide the necessary components for glycogen synthesis in the liver.

Question 6

What is the only substrate used in glycogenesis in muscles?

Answer 6

Blood glucose

Muscles rely solely on blood glucose for glycogen synthesis.

Question 7

What is the first step in glycogenesis?

Answer 7

Formation of UDP-Glucose

This step involves glucose-1-phosphate reacting with UTP.

Question 8

What initiates the glycogenesis process?

Answer 8

UDP-glucose reacts with glycogen primer or glycogenin

This reaction is crucial for starting the formation of glycogen.

Question 9

Which enzyme is key for the elongation step in glycogenesis?

Answer 9

Glycogen Synthase

Glycogen Synthase is essential for adding UDP-glucose to the growing glycogen chain.

Question 10

What is the role of the Branching Enzyme in glycogenesis?

Answer 10

Transfers 5-8 glucose residues to create α-1,6 linkages for branching

This enzyme is responsible for introducing branches into the glycogen molecule.

Question 11

Define glycogenolysis.

Answer 11

Breakdown of glycogen into glucose (liver) or lactate (muscles)

Glycogenolysis is the process that releases stored glucose from glycogen.

Question 12

What is the first step in glycogenolysis?

Answer 12

Phosphorylation

This involves the removal of glucose units as glucose-1-phosphate.

Question 13

What enzyme shifts glucose units during glycogenolysis?

Answer 13

Transferase

This enzyme is involved in the debranching of glycogen.

Question 14

What is the function of the Debranching Enzyme in glycogenolysis?

Answer 14

Hydrolyzes the last α-1,6 linked glucose unit

This step is necessary to fully break down glycogen into usable glucose.

Question 15

What is the conversion that occurs after glucose-1-phosphate in glycogenolysis?

Answer 15

Glucose-1-phosphate → Glucose-6-phosphate (via mutase enzyme)

This conversion is a key step in the breakdown of glycogen.

Question 16

What happens to glucose-6-phosphate in the liver?

Answer 16

Converted to glucose by glucose-6-phosphatase for blood glucose maintenance

This process is vital for regulating blood sugar levels.

Question 17

What happens to glucose-6-phosphate in muscles?

Answer 17

Enters glycolysis to produce lactate (no glucose-6-phosphatase)

Muscle cells use glucose-6-phosphate for energy production rather than for maintaining blood glucose levels.

Question 18

List the key enzymes involved in glycogenesis.

Answer 18

Question 19

List the key enzymes involved in glycogenolysis.

Answer 19

• Phosphorylase
• Debranching Enzyme

These enzymes facilitate the breakdown of glycogen into glucose.

Question 20

What is the clinical significance of liver glycogen?

Answer 20

Maintains blood glucose during fasting

Liver glycogen is essential for preventing hypoglycemia in fasting states.

Question 21

What is the clinical significance of muscle glycogen?

Answer 21

Provides energy during exercise

Muscle glycogen is crucial for sustaining physical activity.