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Glycogen Shit
Exam 3
48
Biochemistry
Undergraduate 3
04/04/2016

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Term
3 steps in the initial breakdown of glycogen to glucose
Definition
glycogen --> glucose-1-phosphate --> glucose 6-phosphate
Term
2 enzymes coordinately regulated for the regulation of glycogen metabolism
Definition
phosphorylase & synthase
Term
what enzyme controls phosphorylation hormonal control for glycogen metabolism
Definition
protein kinase a
Term
protein kinase a
Definition
controls phosphorylation/dephosphorylation events
Term
contrast the effect of phosphorylation on glycogen phosphorylase vs glycogen synthase activity
Definition
increases glycogen phosphorylase activity, decreases glycogen synthase activity
Term
towards what process does phosphorylation flux glycogen activity
Definition
glycogenolysis
Term
what does liver tissue respond to?
Definition
only [glucose] (NOT own energy state, not ATP & AMP levels)
Term
Why does liver tissue not respond to energy charge?
Definition
it doesn't vary metabolically
Term
Does AAMP activate liver phosphorylase?
Definition
NO!
Term
How does glucose binding affect liver phosphorylase?
Definition
glucose binding inactivates phosphorylase by shifting the equilibrium from R to T
Term
What is the main structure of glycogen synthase?
Definition
a tetramer of identical subunits
Term
two conformations of glycogen synthase
Definition
T and R
Term
What is an activating allosteric modulator of glycogen synthase?
Definition
glucose-6-P
Term
3 allosteric inhibitors of glycogen synthase
Definition
1. ATP
2. ADP
3. Pi
Term
How does dephosphorylation affect glycogen synthase?
Definition
phosphorylation turns OFF synthase
Term
How does phosphorylation affect phosphorylase?
Definition
turns ON phosphorylase
Term
type O glycogen storage disease (identified 1964)
Definition
characterized by morning drowsiness, fatigue, convulsions due to hypoglycemia (low blood sugar), high levels of blood glucose & lactase after meals
Term
causes of type O glycogen storage disease
Definition
liver deficient in glycogen & a lack of glycogen synthase
Term
Are synthesis (anabolic) & degradative (catabolic) pathways dependent or independent?
Definition
independent, but somehow they must communicate
Term
Are glycogen granules highly or lowly hydrated (surrounded by water)?
Definition
highly hydrated; OH groups cause H bonding
Term
Why is the T conformation of glycogen phosphorylase less active?
Definition
it has a buried active site & low substrate affinity
Term
Why is the R conformation of glycogen phosphorylase more active?
Definition
it has an accessible active site & high substrate affinity
Term
allosteric activators of glycogen phosphorylase
Definition
AMP (indicates low energy) which promotes move to more active
Term
3 allosteric inhibitors of glycogen phosphorylase
Definition
ATP, glucose 6-P, & glucose prevents the move to more active
Term
Where does AMP bind for glycogen phosphorylase & what does it do?
Definition
the allosteric site in the T state to promote the T to R conformational change
Term
Where do inhibitors bind for glycogen phosphorylase & what do they do?
Definition
the allosteric site in T state to prevent T to R conformational change
Term
What is released by pancreas in response to low blood sugar?
Definition
glucagon
Term
What is released by adrenal cortex in response to stress?
Definition
epinephrine
Term
2 epinephrine receptors on liver cells
Definition
1. activates cAMP --> second messenger that activates enzyme needed for phosphorylation
2. triggers Ca2+ release --> partially activates protein kinase a
Term
How does epinephrine act on muscle receptors?
Definition
activates beta-adrenergic receptor, causing release of camp
Term
When is insulin released?
Definition
in response to high blood glucose
Term
How does insulin binding affect muscle?
Definition
it binds the insulin receptor, activates kinases that inactivate glycogen synthase kinase, drives pathway towards glycogenesis
Term
2 activities controlled by glycogen debranching enzyme
Definition
1. alpha (1-4) transglycolase (transfer of alpha (1-4) trisaccharide to non-reducing end of glycogen)
2. alpha (1-6) glycosidase (removes alpha (1-6) bound glucose at branching point in a hydrolysis reaction)
Term
phosphoglucomutase
Definition
an isomerase that catalyzes reversible conversion of glucose-1-P to glucose-6-P
Term
Where is glucose-6-phosphatase primarily found?
Definition
in the liver
Term
glycogenolysis
Definition
glycogen degradation
Term
3 enzymes involved in glycogenolysis
Definition
1. glycogen phosphorylase
2. glycogen debranching enzyme
3. phosphoglucomutase
Term
glycogen phosphorylase
Definition
breaks alpha 1,4 linkages in the reaction: glycogen(n) + Pi --> glycogen(n+1) + glucose-1-phosphate
Term
What is the rate determining step of glycogenolysis?
Definition
glycogen phosphorylase
Term
From what vitamin is PLP derived?
Definition
vitamin B6
Term
What is the energy storage molecule in animal cells?
Definition
glycogen
Term
describe the structure of glycogen
Definition
a highly branched polymer of D-glucose that branches every 8-12 residues with each branch ending in nonreducing sugar unit
Term
How are glucose units removed from glycogen?
Definition
glucose units removed sequentially from nonreducing ends; cleavage can occur on multiple branches simultaneously
Term
2 tissues in which glycogen is used for storage
Definition
1. liver (most abundant...stored in granules)
2. skeletal muscle (energy source for movement)
Term
5 steps for making a new glycogen molecule
Definition
1. attach glucose to Glycogenin (Tyr residue ha OH that can form bond with glycogen)
2. Glycogenin complexes with glycogen synthase
3. glyogenin-synthase adds up to 7 more glucose residues (using the UDP-glucose substrate, Glycogenin adds glucose (NOT SYNTHASE))
4. glycogen synthase takes over once chain is > 8 residues long
5. glyogenin dissociates from synthase but remains bound to reducing end of glycogen molecule
Term
glycogenesis
Definition
glycogen synthesis that takes place via the reaction: glycogen(n) + UDP-glucose --> glycogen(n+1) + UDP
Term
3 enzymes used for glycogenesis
Definition
1. UDP-glucose pyrophosphorylase
2. glycogen synthase
3. glycogen branching enzyme
Term
Can glycogen synthase start from glucose?
Definition
no!
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