Lecture 23, Glyc Metabolism II (Zaidi) Flashcards
Why is the regulation of glycogen metabolism important?
Maintain blood sugar and provide energy to muscles
T or F: The pathways of glycogen metabolism synthesis and degradation are independent.
True.
What allows for the separate regulation of glycogen metabolism?
Pathways of synthesis and degradation are independent
What are the 2 key enzymes of glycogen metabolism?
Glycogen synthase and glycogen phosphorylase
Which enzyme is the rate limiting step on glycogen metabolism synthesis?
Glycogen synthase
Which enzyme is the rate limiting step on glycogen metabolism degradation?
Glycogen phosphorylase
How are glycogen synthase and glycogen phosphorylase regulated? What is this under the control of?
By allosteric regulators and by reversible phosphorylation (effects are in opposite directions); Under the control of hormones
What are the 2 forms that glycogen synthase exists in?
Active, non-phosphorylated A form; Inactive, phosphorylated B form
What is the interconversion of the 2 forms of glycogen synthase mediated by?
Covalent modification
Which enzymes phosphorylates glycogen synthase?
Several kinases, but most importantly glycogen synthase kinase (GSK)
What is GSK under the control of?
Insulin and PKA
What is the relationship between G6P and glycogen synthesis?
G6P provides allosteric regulation of glycogen synthase (powerful activator); Stabilizes the active form of the enzyme
What are the 2 forms that glycogen phosphorylase exists in?
Active A form (relaxed) in liver; Inactive B form (tense) in muscle
T or F: The isozymes of glycogen phosphorylase exist in excess of R and small amounts of T.
False. Both isozymes of glycogen phosphorylase exist in equilibrium between R and T.
What is glycogen phosphorylase regulated by?
Several allosteric effectors (signal energy state of cell) and reversible phosphorylation (responsive to hormones)
Why is GP called an isozyme?
GP in the liver and in the muscle are the products of separate genes
How does GP different in the liver and the muscle?
In sensitivity to regulatory molecules
Describe the activation of liver GP.
Inactivated by free glucose (indicator of blood sugar levels), unaffected by AMP
Describe the activation of muscle GP.
Allosterically activated by AMP (measure of low energy status of cell)
What is Hers disease caused by?
Mutation in liver GP
What is McArdle syndrome caused by?
Mutation in muscle GP
Describe the allosteric regulation of liver GP.
Default A (active) form, inactivated by glucose
How is liver GP inactivated by glucose?
Glucose binds to active site and stabilizes conformation in the T (inactive) state; When glucose levels are high, there is no need for glycogen breakdown
Describe the allosteric regulation of muscle GP.
Default B (inactive) form, activated by AMP