Regulation of Glycogenesis & Glycogenolysis (Exam 2) Flashcards
(TRUE/FALSE)
Glycogen synthase and glycogen phosphatase both catalyze irreversible reactions.
TRUE
How is glycogen phosphatase regulated?
- Allosterically
- Covalent modulation
What are the effectors of allosteric regulation in glycogen phosphatase?
- ++ AMP (low energy levels)
- – ATP (high energy levels)
If glycogen phosphorylase is phosphorylated, is it active or inactive?
Which enzyme phosphorylates glycogen phosphorylase?
ACTIVE = PHOS (Glycogen phos A)
Phosphorylase kinase activates the enzyme, converts B to A
If glycogen phosphorylase is dephosphorylated, is it active or inactive?
Which enzyme DEphosphorylates glycogen phosphorylase?
INACTIVE = DEPHOS (Glycogen phos B)
Phosphoprotein phosphatase inactivates this enzyme, converts A to B
What is the key regulatory enzyme in glycogenesis?
Glycogen synthase
What is the key regulatory enzyme in glycogenolysis?
Glycogen phosphorylase
(TRUE/FALSE)
cAMP does inhibit glycolysis in muscle.
FALSE
It does NOT
Explain the amplification mechanism and its effect on glycogenolysis.
The amplification mechanism is that one molecule of glucagon or epinephrine causes activation of cAMP signaling cascade which produces an enormous number of glucose-1-P molecules within a few seconds due to the increased surface area of glycogen due to branching.
How is glycogen phosphatase allosterically regulated?
++ AMP (AMP is high during times of low energy levels within the cell)
– ATP (signals intracellular energy levels are high, so there is no need to start breaking down glycogen).
Through what 2 enzymes is glycogen phosphorylase covalent modulated?
Phosphorylase kinase and phosphoprotein phosphatase
When is glycogen phosphatase active?
ACTIVE = PHOSPHORYLATED (Glycogen phos A)
Phosphorylase kinase ACTIVATES the E, converts B to A
When is glycogen phosphatase inactive?
INACTIVE = DEPHOS (Glycogen phos B)
Phosphoprotein phosphatase INACTIVATES the E, converts A to B
How is glycogen synthase allosterically regulated?
++ Glucose-6-P
– CAMP
In what state is glycogen synthase covalently activated?
ACTIVE = DEPHOS (Glycogen synthase A), this is catalyzed by ONE kinase (PHOSPHORYLASE KINASE) at ONE iste
In what state is glycogen synthase covalently inactivated?
INACTIVE = PHOS (Glycogen synthase B), this is catalyzed by 11 different kinases, acting as second messengers (cAMP, Ca2+, etc).
How is the covalent regulation of glycogen synthase different from glycogen phosphorylase?
The covalent regulation of glycogen synthase is much different, in that glycogen phosphorylase can only be phosphorylated by one specific protein (protein kinase), whereas glycogen synthase can be inactivated and shut down by at least 11 different kinase enzymes.
How is glycogen synthase activated by insulin?
Insulin promotes the activation of glycogen synthase through activating phosphoprotein phosphatase activity by dephosphorylating glycogen synthase A; therefore, stimulating glycogenesis.
