chapter 24 Flashcards
1 glycogen contains how many glucose residues
55,000
glycogen phosphorylase degrades glycogen from
the non-reducing ends of the molecule
glycogen phosphorylase catalyzes a reaction that yields
glucose-1-phosphate
glucose-1-phosphate is converted into
glucose 6-phosphate
what does phosphoglucomutase do
converts glucose-1-phosphate to glucose 6-phosphate
glycogen phosphorylase can only cleave
a-1,4-glycosidic bonds
glycogen phosphorylase can not cleave
near branch points
what does the transferase do
shifts a small oligosaccharide near the branch point to a nearby chain, removing the branch and making this accessible for the phosphorylase
what does the debranching enzyme do
cleaves the a-1,6 bond at the branch point, releasing a free glucose
what amino acid is phosphorylated at the active site of phosphoglucomutase
serine
what does glucose-6- phosphatase do in the liver
generates a free glucose that is then released into the blood for use by other tissues such as the brain and red blood cells
what is the key regulatory enzyme for glycogen degredation
glycogen phosphorylase
what are the two states of the phosphorylase
R state and T state
what are the two forms of the phosphorylase
a and b form
how does the a form differ from the b form
the serine residue is phosphorylated
what state is favored in the b form
the t state
what state is favored in the a form
the r state
what is the default form and state of the liver
the a form in the R state
what does the default state of the liver mean in simpler terms
liver phosphorylase is prepared to generate blood glucose unless signaled otherwise
what kind of regulator is glucose
a negative regulator because it facilitates the transformation from the r state to the t state
what is the default form and state of phosphorylase in muscle
b form in the t state
what stabilizes the r state in muscle
the phosphorylase binds AMP
what stabilizes the t state in muscle
ATP and glucose 6-phosphate
what does phosphorylase kinase do
converts glycogen phosphorylase b to phosphorylase a with the addition of a phosphate
what does the conversion from phosphorylase b to a do
makes the enzyme more active
what activates phosphorylase kinase
phosphorylation and calcium ions
what transmits the signal for glycogen breakdown
G proteins
how is glycogen degradation turned off
- hormones that stimulate glycogen breakdown are no longer present
- inherent GTPase activity of the Ga subunit inactivates G protein signaling
- phosphodiesterase converts cAMP into AMP, which does not stimulate protein kinase A
- protein phosphatase 1 removes phosphoryl groups from phosphorylase kinase and glycogen phosphorylase, inactivating the enzymes
