Glycogenesis and Carbohydrate Metabolism

Flashcards based on the lecture notes about glycogenesis and carbohydrate metabolism, covering definitions, processes, and regulatory mechanisms.

What is glycogen and where in the body is it stored?

Glycogen is a polysaccharide of D-glucose stored mainly in muscle (~400 g) and liver (~100 g).

What are the key steps in glycogenesis?

1. Glucose-6-P is converted to Glucose-1-P. 2. Glucose-1-P is incorporated into glycogen as UDP-glucose, catalyzed by pyrophosphorylase.

What is the role of glycogenin in glycogenesis?

Glycogenin serves as the primer for glycogen synthesis, initiating the formation of a glucose chain.

Why is glycogen branched?

Branching allows for a highly soluble polysaccharide with larger size and accelerates the rate of synthesis by increasing the number of nonreducing ends.

What drives glycogenesis forward?

The hydrolysis of pyrophosphate (PPi) by pyrophosphatase, which is highly exergonic.

How does insulin regulate glycogenesis?

Insulin promotes glycogen storage by activating phosphatases that dephosphorylate glycogen synthase, making it more active.

How does glucagon regulate glycogenesis?

Glucagon inhibits glycogenesis by activating kinases that phosphorylate glycogen synthase, rendering it inactive.

What is the significance of the conversion of glucose to UDP-glucose during glycogenesis?

UDP-glucose is the activated form of glucose that is used for glycosylation during glycogen synthesis.

What enzymes are involved in glycogenesis?

Key enzymes include glycogenin, pyrophosphorylase, glycogen synthase, and branching enzyme (4:6 transferase).

What is the metabolic fate of excess glucose in the body?

Excess glucose is stored as glycogen or converted to fatty acids for long-term energy storage.

What is glycogen and where in the body is it stored?

Glycogen is a polysaccharide of D-glucose stored mainly in muscle (~400 g) and liver (~100 g).

What are the key steps in glycogenesis?

1. Glucose-6-P is converted to Glucose-1-P. 2. Glucose-1-P is incorporated into glycogen as UDP-glucose, catalyzed by pyrophosphorylase.

What is the role of glycogenin in glycogenesis?

Glycogenin serves as the primer for glycogen synthesis, initiating the formation of a glucose chain.

Why is glycogen branched?

Branching allows for a highly soluble polysaccharide with larger size and accelerates the rate of synthesis by increasing the number of nonreducing ends.

What drives glycogenesis forward?

The hydrolysis of pyrophosphate (PPi) by pyrophosphatase, which is highly exergonic.

How does insulin regulate glycogenesis?

Insulin promotes glycogen storage by activating phosphatases that dephosphorylate glycogen synthase, making it more active.

How does glucagon regulate glycogenesis?

Glucagon inhibits glycogenesis by activating kinases that phosphorylate glycogen synthase, rendering it inactive.

What is the significance of the conversion of glucose to UDP-glucose during glycogenesis?

UDP-glucose is the activated form of glucose that is used for glycosylation during glycogen synthesis.

What enzymes are involved in glycogenesis?

Key enzymes include glycogenin, pyrophosphorylase, glycogen synthase, and branching enzyme (4:6 transferase).

What is the metabolic fate of excess glucose in the body?

Excess glucose is stored as glycogen or converted to fatty acids for long-term energy storage.

What enzyme catalyzes the conversion of Glucose-6-P to Glucose-1-P in glycogenesis?

Phosphoglucomutase.

What type of glycosidic linkage does glycogen synthase form?

Glycogen synthase forms \alpha-1,4 glycosidic linkages between glucose units.

What is the function of the branching enzyme (4:6 transferase) in glycogen synthesis?

The branching enzyme transfers a block of 6-7 glucose residues from the non-reducing end of a glycogen chain (at least 11 residues long) to an interior glucose residue to form an \alpha-1,6 glycosidic linkage.