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34 Cards in this Set
- Front
- Back
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1. What is the structure of glycogen?
How does branching affect degradation of glycogen? |
α-1,4 linked glucose residues w/ branched attached by α-1,6 linkages
Lots of branching = faster break down -degradation occurs at branch points |
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2. From what is glycogen synthesized?
What supplies the glucose moities? Where are these added? How are the branches produced? |
From glucose
UDP-glucose Added to the non-reducing ends of glycogen primer by glycogen synthase Branching enzyme (glucosyl 4:6 transferase) |
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3. What is produced from glycogen degradation?
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Glucose 1-P (major product) and some free glucose
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4. How does glycogen degradation occur?
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1. Remove glucose units from non-reducing end of glycogen chain
-phosphorylase (enzyme_ -produce glucose 1-P 2. Glucosyl transferase moves glucose units at branch point to non-reducing end of another chain 3. Remaining α-1,6 linked glucose at branch point is released as free glucose |
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5. What is liver glycogen used for?
What stimulates its breakdown? What is muscle glycogen used for? What stimulates its breakdown? |
Maintain blood glucose during fasting
Glucagon and epinephrine Generate ATP for muscle contractions Epinephrine (via cAMP) |
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6. What is the glucose donating molecule of glycogen synthesis?
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UDP-glucose (energetically equivalent to ATP)
Donate glucose molecule one at a time to growing glycogen chain |
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7. Which enzymes phosphorylate glucose?
What do they form? Which enzyme dephosphorylates glucose 6-P to glucose? |
Hexokinase and glucokinase (liver)
Glucose 6-P Glucose 6-phosphotase |
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8. What is the rate limiting step in glycogen synthesis?
What enzyme is involved? What other enzyme is important in glycogen synthesis? What happens if a person lacks this enzyme? |
Adding glucose unit from UDP-glucose to glycogen core
Glycogen Synthase 4:6 transferase (branching enzyme) If lack branching enzyme don't survive |
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9. What is the rate limiting step in glycogen degradation?
What is the enzyme involved? What other enzyme is important in glycogen degradation? |
Adding P to glucose
(glycogen core to glucose 1-P) Phosphorylase 4:4 transferase (debrancher enzyme) |
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10. What stimulates glycogen degradation?
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Glucagon
Degradation is stimulated (synthesis inhibited) when the enzymes of glycogen metabolism are phosphorylated |
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11. What hormones activate adenyl cyclase in the cell membrane to convert ATP to cAMP?
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Glucagon and epinephrine
Glucagon acts on liver cells Epinephrine acts on both liver and muscle cells |
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12. What effects does cAMP have?
What does PKA do? |
Activates protein kinase A
1. Phosphorylates glycogen synthase (less active, decrease glycogen synthesis) 2. Causes phosphorylase to be activated (increase glycogen degradation) |
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13. How does PKA active phosphorylase?
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1. Phosphorylates phosphorylase kinase
2. Phosphorylase kinase adds a phosphate to phosphorylase (active form) |
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14. What does insulin do to glycogen degradation?
What enzyme does it activate? |
Inhibits degradation (stimulate synthesis)
Reverses all phosphorylations stimulated by glucagon Activates the enzyme protein phosphotase |
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15. Steps of glycogen degradation.
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1. ATP --> cAMP
2. Activate protein kinase A (PKA) 3. Phosphorylate phosphorylase kinase 4. Phosphorylate phosphorylase 5. Glycogen --> glucose 1-P **also phosphorylate glycogen synthase (inactive) |
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16. Steps of glycogen synthesis.
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1. Glucose --> glucose 6-P
2. Glucose 1-P 3. UDP-glucose 4. Protein phosphotase dephosphorylated glycogen synthase (active) 5. UDP-glucose + glycogen synthase form glycogen |
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17. What is turned off during glycogen synthesis?
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1. cAMP --> AMP
2. Phosphorylase becomes inactive (protein phosphotase) 3. Phosphorylase kinase becomes inactive (protein phosphotase) **Dephosphorylating the enzymes so become inactive |
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18. What turns glycogen degradation on and glycogen synthesis off?
What turns glycogen degradation off and glycogen synthesis on? |
Glucagon
Insulin |
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19. What does gluconeogensis occur from?
Where does it occur? When does it occur? |
Alanine, Lactate, and Glycerol
Liver only Fasting state |
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20. Is glucose generated from simple reversal of glucose?
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No b/c gluconeogensis involves enzymatic steps that do not occur in glycolysis
Have 3 irreversible steps in glycolysis so have to go around them |
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21. What are the three irreversible steps in glycolysis that must be circumvented?
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1. Pyruvate kinase
(form pyruvate) 2. Phosphofructokinase 1 (PFK-1) (form fructose 1,6-bisP 3. Glucokinase (form glucose 6-P_ |
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22. How does gluconeogensis begin?
What happens to pyruvate? Where does this occur? What enzyme is involved? |
Alanine, glycerol, and lactate are converted to pyruvate
Pyruvate --> Oxaloacetate In mitochondria of liver cells Pyruvate carboxylase |
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23. What is the second irreversible step of gluconeogensis?
What enzyme catalyzes this reaction? |
Oxaloacetate --> Phosphoenolpyruvate
Phosphoenolpyruvate carboxykinase |
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24. How is fructose 1,6-bisP reformed?
What next irreversible step happens to fructose 1,6-bisP? What enzyme catalyzes this reaction? |
Reversal of glycolysis steps
Fructose 6-P Fructose 1,6-bisphosphatase |
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25. Finally, how is free glucose formed?
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Glucose 6-P --> Glucose
Glucose 6-phosphatse |
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26. Gluconeogensis occurs when which enzymes are relatively inactive?
Five enzymes |
1. Pyruvate dehydrogenase
2. Pyruvate kinase 3. PFK 1 4. Glucokinase 5. Hexokinase **prevent futile cycle |
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27. Which four enzymes are unique to gluconeogensis?
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1. Pyruvate carboxylase
2. Phosphoenolpyruvate carboxykinase 3. Fructose 1,6-bisphosphatase 4. Glucose 6-phosphatase |
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28. How much energy is required for the synthesis of one mole of glucose from two moles of pyruvated?
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Energy equivalent to 6 ATP
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29. What is the major regulator of gluconeogensis and glycolysis?
How is this enzyme in the fed state? How is this enzyme in the fasting state? |
Fructose-2.6 bisphosphate (F-2,6-P)
Increases in response to insulin Decreases in response to glucagon |
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30. When F-2,6-P increases, what happens?
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Activate PFK-1 and glycolsis
Inhibit fructose 1,6-bisphosphatase and gluconeogensis |
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31. What happens when F-2,6-P decreases?
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Activate fructose 1,6-bisphosphatase and gluconeogensis
Inhibit PFK-1 and glycolysis |
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32. During fasting, what additional regulations are there?
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1. Glucagon (via cAMP and protein kinase A) phosphorylates and inhibits pyruvate kinase (glycolysis)
2. Acetyl CoA (from β-oxidation of FA) stimulate pyruvate carboxylase |
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33. What additional regulation does insulin provide?
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Through protein phosphatase, it reverse phosphorylation of pyruvate kinase (active and there is glycolysis)
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34. Glucagon induces the synthesis of what 3 gluconeogenic enzymes?
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1. Pyruvate carboxylase
2. Fructose 1,6-bisphosphatase 3. Glucose 6-phosphatase |
