Exercise on Regulation of Carbohydrate Metabolism |
|
|
Exercise on Regulation of Carbohydrate Metabolism
1. This diagram summarizes glycolysis, focusing on the irreversible reactions.
If you want to use this diagram for answering 1 and 3, write all your answers to question 1 on just one side of the diagram.
a. If any molecule is an allosteric modulator, draw an arrow from the molecule to the enzyme it affects and add either + (activates) or − (inhibits) at the arrow.
b. Write in additional modulators and use the same method to show the enzymes they affect and whether the effect is activation or inhibition.
2. For a skeletal muscle cell with low [AMP].
a. What [modulator], if any, increases when PFK-1 is inhibited?
b. What other regulated enzyme is affected by the increase and what is the effect on enzyme activity?
c. What [modulator], if any, increases when pyruvate kinase is inhibited?
3. Activation of PKA in a liver cell affects the activity of two of the enzymes.
a. Write PKA on the side, next to each of the enzymes whose activity it affects.
b. Draw an arrow with a solid line from PKA to the enzyme if PKA directly modifies the enzyme. Draw an arrow with a dashed line if PKA only indirectly affects the enzyme.
c. Add either + or − to each arrow to show whether the effect is activation or inhibition.
4. How would your answers to question 3 be different for a skeletal muscle cell? |
|
5. Allosteric and covalent regulation respond to different conditions.
a. Which modulator shown in the diagram above changes concentration in response
to covalent regulation? Does it reflect a change in extracellular or in intracellular
conditions?
b. Do the other modulators change concentration as a result of changes in
extracellular or intracellular conditions?
6. Fill in the diagram below by adding the molecules (structures), enzymes, and coenzymes for the four reactions.
7. Describe regulation of PFK-2 and FBPase-2 activity in the liver using Table 1.
Table 1: PFK-2 and FBPase-2 |
| enzyme |
PFK-2 |
FBPase-2 |
substrate |
|
|
product |
|
|
activated by* |
|
|
inactivated by* |
|
|
effect of activation† |
|
|
*Name the enzyme.
†Which pathway–glycolysis or gluconeogenesis–is more active?
8. Fill in Table 2 to summarize the effects of these enzymes on glycogen phosphorylase.
Table 2: Covalent Regulation of Glycogen Phosphorylase |
| enzyme |
phosphorylase kinase |
PP1 |
Does this act on phosphorylase a or phosphorylase b? |
|
|
What other substrate is required? |
|
|
Does this increase or decrease phosphorylase activity? |
|
|
Is glycogen synthesized or degraded as a result? |
|
|
9. Fill in Table 3 to summarize the effects of PKA and PP1 on glycogen synthase.
Table 3: Covalent Regulation of Glycogen Synthase |
| enzyme |
PKA |
PP1 |
Does this act on glycogen synthase a or glycogen synthase b? |
|
|
What other substrate is required? |
|
|
Does this increase or decrease synthase activity? |
|
|
Is glycogen synthesized or degraded as a result? |
|
|
10. Fill in Table 4 to list the effects of these modulators on glycogen degradation.
Table 4: Modulators that Affect Skeletal Muscle Glycogen Degradation |
molecule |
enzyme the modulator binds |
effect on enzyme activity |
effect on glycogen degradation |
Gsα |
|
|
|
Ca2+ |
|
|
|
glucose-6-P or ATP |
|
|
|
AMP |
|
|
|
11. You could make a table like Table 4 for a liver cell, but you would have to change some of the molecules.
a. Which two molecules stay the same?
b. What change(s) would you make for the other molecules?
12. Carbohydrate metabolism and its regulation involves kinases, phosphatases, and phosphorylases. Distinguish between them by filling in Table 5.
Table 5: Kinase, Phosphatase, and Phosphorylase |
Enzyme |
Kinase |
Phosphatase |
Phosphorylase |
Is ATP required? |
|
|
|
Is Pi a substrate? |
|
|
|
Is Pi a product? |
|
|
|
13. There are three conditions that affect glycogen metabolism–high blood sugar immediately after a meal, low blood sugar a few hours after a meal, and prolonged exercise. Table 6 helps in summarizing how each condition affects glycogen metabolism.
Table 6: Conditions that Affect Glycogen Metabolism |
condition |
hormone secreted |
affects muscle, liver, or both? |
glycogen phosphorylase activity |
glycogen synthase activity |
Is glycogen degraded or synthesized? |
high blood sugar |
|
|
|
|
|
low blood sugar |
|
|
|
|
|
exercise |
|
|
|
|
|
14. In liver cells, two enzymes that determine whether glucose goes through glycolysis or glycogen synthesis are PFK-1 and glycogen synthase.
a. What energy conditions favor each pathway?
b. Which of the two enzymes is regulated by allosteric regulation, what modulators
are involved, and what is the effect of each modulator on enzyme activity?
c. Which of the two enzymes is regulated by covalent modification, what enzymes
are involved, and what is the effect of each on enzyme activity?
top of page