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47 Cards in this Set
- Front
- Back
descriptive name for glycogen
structure of glycogen (bonds) |
branched chain homopolysaccharide made from alpha-D-gluc
alpha 1,4 glycosidic linkages alpha 1,6 about every 8-10 glucose units |
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where is glycogen stored
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cytoplasm in large hydrated granules, each containing ~100,000 gluc units
primarily in liver and muscles |
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is more glycogen stored in muscle or liver
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total glycogen stored in muscle (because there is so much more muscle) is three times that of liver, even though liver has higher concentrations of glycogen
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why not store glucose in fat? or as free glucose?
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cannot convrt fat back to glucose, only glucose to fat
free glucose is osmotically active so need glycogen |
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how does the function of glycogen differ in liver and muscle?
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liver maintains blod glu
muscles supply fuel reserve |
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where is glycogen utilized
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75% brain, the rest is erythrocytes skeletal and heart muscles
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how long does the glycogen supply last in the liver
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less than 24 hours
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what is gluconeogenesis and why would you need glycogen if you have this pathway?
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- the synthesis of glu from small molecules like aa (happens in liver)
is much SLOWER, need fast release hence glycogen |
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muscles and glycogen, why doesnt glucose diffuse out of muscles when it is made from muscle glycogen?
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muscles lack Glucose-6-phosphatase and therefore glucose found in muscles is in the G-6-P form that doesnt diffuse out of cells.
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Four broad steps of glycogen synthesis
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synthesis if UDP glucose
adding of primer elongation branching |
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explain biochemical process of glycogen synthesis
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glucose is taken up into the cell and phosphorylated by hexokinase (glucokinase in liver)
G-6-P is then mutated to G-1-P via phosphoglucomutase G-1-P is converted to UDP-gluc using UTP via uridylyltransferase or UDPGLc pyrophosphorylase |
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explain biochemical process of glycogen synthesis continued
use specific aa sites |
UDP-glucose is attached to glycogenin at OH of tyr 194 via autoglucosylation
glycogenin has a glucosyltransferase activity (note: udp is kicked out in the reaction) |
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explain biochemical process of glycogen synthesis continued
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elongation
new glycosidic bond formed between incoming(activated) C1 OH and the accepting C4 via glycogen synthase adds three at a time alpha 1,4 glycosidic linkage |
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what is special about glycogen synthase?
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it is rate limiting and regulated
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is glycogen synthase's Km for small glycogen molecules large or small
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it's large(ie low affinity)
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glycogen branching
enz? |
glucosyl 4:6 transferase
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how does glucosyl 4:6 transferase work
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transfers 6-8 gluc residues from end of chain to another residue forming an alpha 1,6 bond
hence its 4:6 b/c it breaks an alpha 1,4 bond and makes an alpha 1,6 bond |
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is glucose added to the reducing or nonreducing end of a chain?
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non reducing
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why branch?
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increases glycogen solubility
increases nonreducing ends to which glucosyl residues can be added |
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describe glycogenolysis
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glycogen phosphorylase uses Pi to cleave alpha 1,4, requires PLP (B6 derivative)as coenz
debranching enzyme: 4-alpha-D-glucotransferase, removes outer 3 of limit dextrin and attaches to a nonreducing end, amylo-alpha1,6,glucosidase cleaves last glucose |
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decribe the debranching enzyme and the two catalytic sites (bifunctional)
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debranching enzyme: 4-alpha-D-glucotransferase, removes outer 3 of limit dextrin and attaches to a nonreducing end, amylo-alpha1,6,glucosidase cleaves last glucose usig water
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whats the ratio of glucoses released from phosphorylase to debranching enz
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12:1
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how else can you degrade glycogen?
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lysosomal glycogen degradation 1-3%
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REGULATION
glycogen phosphorylase is active or inactive when phosphorylated |
active when phosphorylated
a form active b form inactive |
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what activates glycogen phosphorylase
what inactivates it |
activated via phosphorylase kinase using ATP
inactivated using phosphoprotein phosphatase |
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REGULATION of phosphorylase kinase
what regulates the regulator |
phosphorylated is active
phos'd by protein kinase A dephos'd by phosphoprotein phosphatase |
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glycogen phosphorylase chemical characteristics
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allosteric
T and R states, a is active b/c P shifts equilibrium to R state |
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how is PKA . . released from regulatory sites
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H activates Gprotein receptor causes formation of cAMP
cAMP binds regulatory sites on PKA and releases catalytic portion |
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what does PKA inhibit and how
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phosphoprotein phostphatase
it P's protein phosphatase inhibitor activating it so that protein phosphatase cant change things back into their inactive forms |
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PKA activates phosphorylase kinase which activates glycogen phosphatase releasing glucose
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jkh
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PKA inhibits phosphoprotein phosphatase by activating it's inhibitor(protein phosphatase inhibitor) so that
glycogen phosphorylase isnt turned off |
lkb
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summary of cAMP activation
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inhibits synyhesis (glycogenesis)
increases catabolism (glycogenolysis) |
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cAMP
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activates glycogen phosphorylase kinase and therefore glycogen phosphorylase
inactivates glycogen synthase (because glycogen phosphorylase kinase is activated) activates protein phosphatase inhibitor |
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is glycogen synthase active or inactive when p'd
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inactive
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synthesis vs catabolism and phosphorylation
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synthesis is inactive when p'd
catab is active when p'd |
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synthesis vs catabolism and phosphorylation
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synthesis is inactive when p'd
catab is active when p'd |
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Insulin and glycogen synthesis
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maybe:
inhibition of protein kinases, activation of phosphoprotein phosphatase glycogen synthase is de P'd (active) phosphorylase kinase and phosphorylase are de P'd (inactive) |
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insulin and glycogen synthesis
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promotes
conversion of cAMP to 5'AMP |
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what are allosteric effectors?
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bind enz regulatory site to promote R or T state
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what is the effector of phophorylase kinase b (catab)
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Ca, will activate this even though it's dephosed
binds delta subunit, conf change activates gamma |
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what is the effector of phosphorylase b
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AMP, activates it, in muscles
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effector of phosphorylase a
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glucose, inhibits it , only hepatic
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effector of synthase b
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G-6-P, activates, in both liver and muscle
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how does Ca activate glycogenolysis in liver?
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Ca increased in liver due to epi binding alpha-adrenergic receptors
this activates phospholipase C generating IP3 and DAG IP3 causes Ca release in cytosol which activates glycogenolysis |
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AMP to ATP ratio, if increased reflects what?
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low energy
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AMP is an allosteric effector of?
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phosphorylase b, activates
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high amp to atp ratio means what
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activation of catabolism
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