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50 Cards in this Set

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Where is glycogen found?
In all cell types in tissues that respond to fuel hormones
What two factors increase glycogen degradation?
a) low fuel supplies b) response to stress or other metabolic need
What factor increases glycogen synthesis?
excess carbohydrates
In glycogen, what type of linkage do you find in a) branching points… b) linear polymer?
a) ∂-1,6 linkage… b) ∂-1,4 linkage
What is the starting point for glycogen synthesis?
Glycogenin protein acts like a primer (autoglycosylation)
What happens after glycogenin adds 5-7 glucose molecules to the growing poylmer?
glycogen synthase starts elongating the polymer
Where are UDP-glucose molecules added?
At the reducing end
What is the value in having glycogen branch?
Degradation occurs through exoglycosylase, which means it starts at the ends (more branches = more ends = faster degradation)… also more reducing ends = faster synthesis
Which enzyme makes glucose synthesis possible (export)? And where is it found?
a)glucose-6-phosphatase (G6Pase), b) only in the liver
Which organ can dephosphorylate and export glucose?
Only the liver
What can organs, other than the liver, do with glucose?
Use it
What is the chain of events after low blood sugar occurs?
decreased glucagon ratio > glycogenolysis > inhibitioin of glycogen synthesis
What effect does epinephrine have on glycogen?
epi activates glygenolysis to mobilize stored energy
Can muscles make glycogen?
Yes, they have GLUT4, insulin receptors… thus they use glucose for immediate use and to make glycogen
What is the rate limiting enzyme for glycogen degradation?
glycogen phosphorylase
What 3 things stimulate glycogen phosphorylation (glycogen degradation in muscles) during exercise?
epinephrine, AMP, and calcium release during exercise
What is the cost, in ATP, for adding another glucose molecule?
2 ATP
What are the 3 reactive steps in adding another glucose molecule to glycogen (including the enzymes?
glucose enters the cell...a) glucose + ATP -> glucose 6-phosphate (hexokinase or glucokinase) +ADP… b) G6P -> G1P (phosphoglucomutase)… c) G1P -> UDP-glucose (UDP-glucose pyrophosphorylase)
What impact does the fact that hexokinase has a low Km and glucokinase has a high Km for the liver's role in the body?
the liver is involved in homeostasis to generate G6P
While the glycogenin protein can autoglycosylate, what 2 things does it require?
UDP-glucose and Mg-Mn
What are the 3 steps in the degradation of glycogen in the liver (and kidneys)?
a) glycogen + Pi -> glycogen + G1P (no high energy bonds broken here) … b) G1P -> G6P (phosphoglucomutase)… c) G6P -> Glucose (G6-phosphatase)… leaves the liver (or kidney)
What are the 3 steps in the degradation of glycogen in muscles?
a) glycogen + Pi -> glycogen + G1P (no high energy bonds broken here) … b) G1P -> G6P (phosphoglucomutase)… c) glycolysis
When glucose is added to a growing glycogen polymer what enzyme catalyzes this reaction and what is lost?
Glycogen synthase… UDP
Which enzyme takes a linear segment and moves it?
Tranferase
In terms of the linkage, what does the Tranferase do?
It breaks a ∂-1-4 linkage, moves the strand and reattaches it using a ∂-1,6 linkage, forming a new branch.
In glycogen degradation, from glycogen(n+1) + Pi --> glycogen (n) + glucose-1-P, are high energy P bonds broken?
No
In glycogen degradation, what converts glucose-1-P to G-6-P?
phosphoglucomutase
In the liver (or kidney) what is the fate of G6P upon glycogenolysis?
glycolysis or cellular export
In glycogen synthesis, which enzyme starts a new branch?
4,6-transferase
In glycogen degradation, which enzyme breaks the 1,4 linkage? And what else is needed to make ~8 G1P?
glycogen phophorylase… 8 Pi
In glycogen degradation, what is the role of transferase? What is the remaining 1,6 linked glucose is removed by?
a) transferase removes about 3-4 residues and place them at the end of another polymer using a 1,4 linkage… b) ∂-1,6 glucosidase
What is the product of ∂-1,6-glucosidase?
glucose
What is the product of transferase?
G1P
Which enzyme converts G6P to G1P?
phosphoglucomutase
What is special about G1P?
It is the intermediate point for glycogen synthesis and glycogen degradation
Which moiety is in the central position in carbohydrate metabolism (glycogen synthesis), and is also involved in the synthesis of proteoglycans, glycoproteins, and a precursor for lactose in mammary tissue?
UDP-glucose
What are the regulators of glycogen stores in the liver after exercise or stress? And what effect do they have on the liver?
(+) blood epi… (+) tissue cAMP… (Ca2+ (+)… b) they ALL cause degradation of glycogen and inhibit synthesis.
What effect does decreased tissue cAMP have on glycogen stores in the liver?
tissue degradation down… synthesis up… with increased cAMP the opposite would be true
What effect do the increase in bloood epi, tissue AMP, Ca2+ calmodulin, and cAMP have on glycogen synthesis, degradation and glycolysis?
glycolysis and degradation of glycogen are up… synthesis of glycogen are down
Is glycogen phosphorylase, which mediates glycogen degradation, active or not active when phosphorylated?
Active
Is glycogen synthase I, which plays a major role in glycogen synthesis, active or not active when phosphorylated?
Inactive
What does the fact that PKA can phosphorylate both glycogen synthase and glycogen phosphorylase imply?
It has opposite effects on two different pathways
What is the step between the allosteric activation of PKA and the activation of the a cellular protein, e.g., deactivation of glycogen synthase?
Active PKA causes the activation (via phosphorylation) of phosphorylation kinase, which activates glycogen phosphorylase, and inactivates glycogen synthase.
What is the role of the protein phosphatase in regulation of glycogen synthesis/degradation?
It dephosphorylates glycogen synthase
What effect do Ca2+ (in response to nerve impulse) and epinephrine have on glycogen synthase/degradation?
It interacts with calmodulin and phosphorylates phosphorylase kinase and ultimately leads to the phosphorylation and deactivation of glycogen synthase.
What effect does increased AMP levels (due to muscle) have on glycogen synthase/degradation? What percentage?
It allosterically activates glycogen phosphorylase and ultimately leads to the phosphorylation and deactivation of glycogen synthase. 80%
What are the fuel sources for muscle from first to last?
muscle glycogen > glucose from blood (from liver glycogen) > fatty acid oxidation from muscle TAG > fatty acid from TAG in adipose tissue
What will a defect in G6-phosphatase (von Gierke's) Type I cause? (in liver) Why? Treatment?
a) enlarged liver, fasting hypoglycemia, growth failure… b) glucose is not exported and G6P stimulates glycogen synthesis. C) treatment is continuous digestion of carbs
What will a defect in amylo1,6 glucosidase (debrancher) Type II cause? (in liver)
Fasting hypoglycemia
What will a defect in muscle glycogen phosphorylase Type III cause? (in muscle)
exercise-induced muscle pain, muscle weakness (muscle isozyme is defective)