CH 25: Glycogen Synthesis

These flashcards cover key concepts related to glycogen synthesis and metabolism in biochemistry, highlighting enzyme functions, regulatory mechanisms, and metabolic pathways.

UDP-glucose is an activated form of glucose that is used to extend the glycogen chain in synthesis.

What is UDP-glucose and what role does it play in glycogen synthesis?

Glycogen synthase.

Which enzyme catalyzes the transfer of glucose from UDP-glucose to a growing glycogen chain?

At least 4 glucose residues.

What is the minimum length of glucose residue oligosaccharide required for glycogen synthase to act?

The glycogen branching enzyme forms α-1,6 linkages by cleaving an α-1,4-linkage and transferring a block of glucose to create branches.

What is the role of the glycogen branching enzyme in glycogen metabolism?

The b form is phosphorylated and inactive while the a form is dephosphorylated and active.

What are the two forms of glycogen synthase and how do they differ?

Glucagon and epinephrine.

What stimulates glycogenolysis and inhibits glycogenesis?

Insulin stimulates glycogen synthesis by increasing GLUT4 expression and activating glycogen synthase.

How does insulin affect glycogen synthesis?

Glycogen synthase is dephosphorylated and converted to the active form.

What happens to glycogen synthase when insulin signaling is active?

Hormonal signals that promote glycogenolysis also inactivate PP1.

What prevents Protein Phosphatase 1 (PP1) from always inhibiting glycogenolysis?

Under conditions of high glucose levels, or the fed state.

During what physiological state is glycogen synthesis favored?

Glucose-1-phosphate and UTP (uridine triphosphate).

What two molecules are essential for the synthesis of UDP-glucose?

Only two molecules of ATP are required to incorporate dietary glucose into glycogen.

Why is glycogen considered an efficient storage form of glucose?

Glucose 6-phosphate acts as a powerful allosteric activator of glycogen synthase b.

How does glucose 6-phosphate regulate glycogen synthase?

PP1 shifts glycogen metabolism from the degradation mode to the synthesis mode by dephosphorylation.

What is the role of Protein Phosphatase 1 in glycogen metabolism?

Glycogen synthase kinase is phosphorylated and inactivated.

What happens to glycogen synthase kinase when insulin signaling is active?

High blood-glucose levels lead to the conversion of liver phosphorylase a to the T state, promoting synthesis.

What is the effect of high blood-glucose levels on liver glycogen metabolism?

Characteristic excess glucose in the blood and underutilization of the fuel.

What is the outcome of insulin insufficiency in Diabetes Mellitus?

Glucagon signaling leads to the inhibition of glycogenesis.

How does the presence of glucagon affect glycogen synthesis?

Glucokinase phosphorylates imported glucose, activating further glycogen synthesis.

What is the role of glucokinase in glycogen synthesis?

31 molecules of ATP.

In muscle cells, how many ATP molecules can be derived from the complete oxidation of glucose from glycogen breakdown?

Most phosphorylase a is converted into b before PP1 is released.

What happens to phosphorylase a during the switching from glycogen degradation to synthesis?

Aretaeus referred to diabetes as the 'passing of water by a siphon,' highlighting symptomatology.

What historical insight was provided about diabetes?

Mellitus comes from Latin and means 'sweetened with honey'.

What is the significance of the term 'Mellitus' in relation to diabetes?

Glycogen synthase.

What is the primary enzyme regulating glycogen synthesis?

It prevents gly-glycogen from being synthesized while being broken down simultaneously.

What does it mean for glycogen metabolism to be reciprocally regulated?

Insulin signaling increases glucose availability and promotes the activation of glycogen synthase.

How does the activation of glycogen synthase occur in response to exercise and carbohydrate intake?