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46 Cards in this Set
- Front
- Back
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Why is glycogen the optimal storage for carbohydrates in cells?
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- Can store several units as a polymer
- Breakdown is faster than taking glucose from blood. |
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What is glycogen used for in the muscle and in the liver?
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Muscles: energy for muscle contraction
Liver: regulation of blood glucose |
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Which enzyme is responsible for the conversion of G6P to G1P? Is it reversible process?
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The reaction by phosphoglucomutase is reversible.
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To which end of glycogen are new glucose units attached?
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The oxidizing end.
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Which reaction drives the synthesis of UDP-glucose from UTP and glucose.
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Hydrolysis of PPi to 2Pi by inorganic pyrophosphotase.
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In which reaction of glycogen synthesis is ATP consumed? Which enzyme catalyses it?
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The formation of UTP nucleoside diphosphate kinase.
UDP + ATP --> UTP + ADP |
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What type of bonds are created in chain elongation of glycogen?
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alpha 1-4 linkage
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Which enzyme is responsible for the conversion of G6P to G1P? Is it reversible process?
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The reaction by phosphoglucomutase is reversible.
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To which end of glycogen are new glucose units attached?
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The oxidizing end.
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Which reaction drives the synthesis of UDP-glucose from UTP and glucose.
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Hydrolysis of PPi to 2Pi by inorganic pyrophosphotase.
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In which reaction of glycogen synthesis is ATP consumed? Which enzyme catalyses it?
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The formation of UTP nucleoside diphosphate kinase.
UDP + ATP --> UTP + ADP |
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What type of bonds are created in chain elongation of glycogen?
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alpha 1-4 linkage
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What are the conditions for the creation of a new branch point on glycogen?
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- Transfered chain is 7 units long.
- Original chain is >11 units long. - New branch point is at least 4 units away from another branch point. |
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Which enzyme creates new branch points in glycogen?
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Amylo-(1-4-->1,6)-transglycosylase
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What is the cost of glycogen synthesis?
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2 ATP
- 1ATP from phosphoglucomutase - 1ATP from synthesis of UTP |
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What is required for glycogen phosphorylase to cut glucose units off?
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Phosphate, since glucose becomes G1P
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Which enzyme creates new branch points in glycogen?
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Amylo-(1-4-->1,6)-transglycosylase
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In glycogen debranching, how many units are transfered to another chain? By what enzyme?
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3 units are transfered by α(1-4) glycosyl transferase at least 5 units away from branch point.
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What happens to the last residue on the chain in glycogen debranching?
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It is hydrolysed by α(1-6) glucosidase to become glucose.
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Why does the last residue on the glycogen chain become glucose?
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Not enough free energy from the cutting of α(1-6) link to reattach it to the chain.
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Which intermediate is formed by phosphoglucomutase during the conversion of G1P to G6P?
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G1,6P
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Why is there a pool of G1,6P in the cell?
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Phosphoglucomutase requires a phosphate group to be attached to it.
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What is the fate of G6P obtained from glycogen degradation in the muscle? In the liver?
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Muscle: continues down glycolytic pathway
Liver: converted to glucose to maintain blood [glucose] |
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What is the fate of G6P obtained from glycogen degradation in the muscle? In the liver?
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Muscle: continues down glycolytic pathway
Liver: converted to glucose to maintain blood [glucose] |
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What effect will an increase in ATP have on glycogen phosphorylase? What effect will this have on it?
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- Modified phosphorylase a will become unmodified phosphorylase b.
- Leads to a decrease in activity. |
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What will activate protein kinase A in muscles?
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cAMP
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What does protein kinase A activate and inhibit?
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Activates:
- phosphorylase kinase - phosphorylase (indirectly) - phosphoprotein phosphotase inhibitor Inhibits: - glycogen synthase |
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Which protein does phosphoprotein phosphotase inhibitor inhibit?
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PP1c
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Which subunit of phosphorylase kinase confers sensitivity to Ca2+?
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Calmodulin subunit
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Which enzyme produces cAMP? What activates this pathway in muscles?
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- Adenylate cyclase
- The binding of a hormone to a receptor causes Gprotein-GTP complex to bind and activate it |
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True or False?
Glycogen synthase b is under allosteric control of [ATP], [ADP] and [Pi]. |
True!
Glycogen synthase a is not under control of these effectors. |
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What causes activation of PP1c in muscles? Is PP1c phosphorylated once or twice?
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Insulin will trigger activation.
Bazinga! PP1c is not phosphorylated, the Gm subunit will be phosphorylated once! |
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How will an increase in blood glucose affect glycogen synthase? Glycogen phosphorylase?
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Glycogen synthase will de dephosphorylated and activated.
Glycogen phosphorylase will also be dephosphorylated, but deactivated. |
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What effect will epinephrine have on PP1c in muscles?
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Double phosphorylation of Gm and inactivation of PP1c through PKA.
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Which enzyme catalyses the hydolysis of PIP2? What are the products of this hydrolysis?
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Phospholipase C hydrolyses PIP2 to IP3 and DAG.
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What does DAG activate? To what effect?
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Activation of Protein Kinase C which inhibits glycogen synthase.
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What does IP3 stimulate?
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The release of Calcium in the ER
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What does the liver do with glycogen when under stress?
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Degrades it and releases it as glucose into the bloodstream.
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What are the 2 signaling molecules for stress in the liver?
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- epinephrine
- glucagon |
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Is the GL PP1 subunit phosphorylated in the liver?
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No, only the GmPP1 subunit in muscles is phosphorylated.
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How does the GL-PP1 function in the liver?
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1) Complexes with phosphorylase.
2) Glucose makes phospho a R-->T. 3) PP1 makes phospho a --> phospho b 4) phospho b has low affinity for PP1 --> no inhibition of PP1 5) activation of glycogen synthase |
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True or False?
There is insulin signaling in the liver? |
False
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Which enzyme releases glucose into the bloodstream?
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G6Pase
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What are the consequences of G6Pase deficiency?
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- Accumulation of glycogen
- Inability to increase blood glucose - Symptoms (massive liver, hypoglycemia, failure to thrive) |
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Which enzyme is affected by Type V glycogen storage disease?
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Muscle glycogen phosphorylase
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What is the difference between Type V and Type VI deficiencies?
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Type V affects muscle phosphorylase (cramps) and Type VI affects liver phosphorylase (hypoglycemia)
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