Term
| Identify the two tissues with the highest concentrations of glycogen |
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Definition
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Term
| Describe the different roles of muscle and liver glycogen |
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Definition
- Muscle glycogen provides glucose only for itself.
- Hepatic glycogen degradation results in and increase in blood glucose, providing glucose for the brain and other tissues that require glucose for energy. |
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Term
| Predict the impact of impaired hepatic glycogen degradation on blood glucose levels |
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Definition
| decreased blood glucose levels, especially between meals or in starved state. |
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Term
| Predict the impact of impaired liver or muscle glycogen degradation on the concentration of glycogen in that tissue |
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Definition
| In both cases, there will be a build up of glycogen in the tissue. |
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Term
| Compare the cascade of enzymes which activates glycogen phosphorylase with that which inhibits glycogen synthase. |
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Definition
It is the same cascade that performs both functions:
Activation of phosphoprotein phosphatase by insulin, causes dephosphorylation and activation of glycogen synthase.
Deactivation of phosphoprotein phosphorylase will occur when cAMP is high, and will result in glycogen phosphorylase staying phosphorylated and active.
Generally, enzymes that are involved in glycolysis or glycogen synthesis will be inhibited by phosphorylation, while enzymes involved in creating glucose (i.e. gluconeogensis and glycogen degradation) will be activated by the same phosphorylation cascade. |
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Term
| Predict the advantage of using a cascade of enzymes to activate glycogen phosphorylase |
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Definition
- amplification
- finer regulation |
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Term
| Identify the enzyme involved with glycogen degradation that contains Ca2+ sensitive protein calmodulin as a subunit |
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Definition
| calmodulin-dependent protein kinase: phosphorylates glycogen synthase (inactivating it), and glycogen phosphatase (activating it) |
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Term
| Identify the three second messenger systems involved with the regulation of glycogen metabolism |
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Definition
Ca2+
cAMP
IP3
- all of which activate phosphorylase kinase |
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Term
| Hypothesize why glycogen phosphorylase is activated by multiple second messenger systems |
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Definition
| - better regulation, easier to activate when body is in need of glucose |
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Term
| Predict the influence of elevated glucose-6-phosphate or AMP on glycogen synthesis and degradation |
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Definition
Elevated AMP will increase glycogen degradation. It allosterically activates glycogen phosphorylase.
Elevated glucose-6-phosphate will increase glycogen synthesis. |
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Term
Identify the specific enzymes and their tissue locations (hepatic and/or muscle) for which a genetic deficiency results in each of the following conditions:
1) Decreased fasting glucose:
2) Increased hepatic glycogen concentration:
3) decreased hepatic glycogen concentration
4) increased muscle glycogen concentration
5) increased fasting lipids
6) reduced ability to perform exercise |
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Definition
1) Decreased fasting glucose: hepatic glycogen phosphorylase (or debranching enzyme)
2) Increased hepatic glycogen concentration: decreased glycogen phosphorylase
3) decreased hepatic glycogen concentration: decreased hepatic glycogen synthase
4) increased muscle glycogen concentration: decreased muscle glycogen phosphorylase (or debranching)
5) increased fasting lipids: decreased hepatic glycogen phosphorylase
6) reduced ability to perform exercise: decreased muscle glycogen phosphorylase |
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Term
| Identify pathways of carbohydrate metabolism that are activated as a result of gluacgon-stimulated cAMP formation, activation of protein kinase A, and phosphorylation of one or more enzymes; list the specific enzymes that are activated by glucagon |
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Definition
Glucagon activates glycogen degradation and gluconeogensis
Gluconeogensis: increases transcription of pyruvate carboxylase, PEP carboxylase, fructose-1,6-bisphosphatase and glucose-6-phosphatase.
It also transcriptionally up regulates PEP carboxy kinase (via CREB and CRE)
Glycogen degradation: Glycogen phosphorylase is activated by glucagon-induced phosphorylation cascade. |
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Term
| Identify the pathways of carbohydrate metabolism that are inhibited as a result of glucagon stimulated cAMP, activation of protein kinase A and phosphorylation of one or more enzymes; list the specific enzymes that are inhibited by glucagon |
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Definition
The three regulatory enzymes of glycolysis are down regulated in the presence of glucagon (hexokinase, PFK1, pyruvate kinase). It also results in covalent inhibition of pyruvate kinase via phosphorylation.
Glycogen synthase is also inhibited by the phosphorylation cascade. |
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Term
| Predict consequences of a tumor that destroys pancreatic beta cells |
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Definition
| pancreatic beta cells create insulin, so a tumor destroying them would decrease insulin and result in a decrease in an up take of glucose, a decrease in glycolysis, a decrease in glycogen synthesis and an increase in glycogen breakdown and gluconeogensis. |
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Term
| Describe the role of glucagon in maintaining blood glucose levels |
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Definition
| glucagon keeps blood glucose levels high enough in the fasted state by activating glycogen degradation and gluconeogensis |
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Term
| Identify the potential uses of ribose-5-phosphate |
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Definition
1) Pentose phosphate pathway and generation of NADPH
2) Pyramidine/Purine synthesis |
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Term
| Identify the potential uses of NADPH |
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Definition
| NADPH is used in lipid biosynthesis and reduction of glutathione, which is used to reduce H2O2 |
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Term
| Predict the effects of a genetic deficiency of glucose-6-phosphate dehydrogenase |
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Definition
| Glucose-6-phosphate dehydrogenase is the rate limiting step in the pentose phosphate pathway. A deficiency would cause a decrease in NADHP, which is crucial in RBC's. This will lead to hemolytic anemia as RBC's lyse due to oxidative stress. |
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