Term
What is UDP- Glucose?
How is it synthesized? |
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Definition
Source of all glucosyl residues that add to the glycogen molecule
UDP-Glucose is synthesized from G1P and UTP by UDP-glucose pyrophosphorylase |
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Term
| Why is glycogen necessary if gluconeogenesis can occur in liver and kidney? |
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Definition
| Gluconeogenesis is a slow process, and glycogen can be metabolized quickly |
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Term
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Definition
Starts with Glycogenin, which accepts glucose residues from UDP-Glucose. This starts to build a chain.
The chain elongates and every 6 or 8 links will lead to a branch.
The use UDP is converted back to UTP |
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Term
| What is the benefit of branching in a glycogen molecule? |
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Definition
| more branches mean more reducing ends to add on, quicker mobilization and quicker sytnehsis because there are more starting sites. |
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Term
| 2 main places glycogen is synthesized and stored |
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Definition
| Liver and skeletal muscle |
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Term
| Primary product of glycogenolysis |
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Definition
| G1P, done by breaking 1-4 or 1-6 bonds (shortening of the chains) |
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Term
| How are glycogen chains shortened? |
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Definition
| Glycogen phosphorylase cleaves bonds down to 4 residues on each chain before a branch point. This is as far as it can degrade |
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Term
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Definition
| rate-limiting enzyme in glycogenolysis |
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Term
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Definition
de-branching enzyme
removes outer 3 or 4 residues at a branch |
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Term
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Definition
In the last step on gluconeogenesis
It converts G6Pase to glucose. Glucose is then transported by GLUT 7 to the cytosol, then out to blood to maintain blood glucose levels |
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Term
| What happens to G6P in muscle? |
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Definition
| There is no G6Pase in the muscle, so G6P enters glycolysis to provide ATP |
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Term
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Definition
lysosomal enzyme that degrades about 1-3% of all glycogen
Mechanism of action is unknown
Deficiency of this enzyme can cause glycogen accumulation in lysosome vacuoles |
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Term
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Definition
abnormal storage of glycogen. Glycogen builds up in the lysosomal vacuoles which alter the lysosome function.
Disease like this can range from mild disorders to fatality (fatality usually in infants) |
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Term
| Regulatory Pathways of Glycogen Synthesis and Degradation |
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Definition
1. glycogen synthase and glycogen phosphorylase are allosterically controlled
2. hormonal regulation (epinephrine) |
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Term
| 2 paths for glycogenolysis |
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Definition
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Term
| How is glycogen degraded in the muscle |
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Definition
Muscle contraction releases Ca++ in S, which binds calmodulin, which activates phosphorylase kinase
(occurs in anorexia or ATP depletion) |
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Term
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Definition
•Glucose binds & inhibits glycogen phosphorylase a, becomes a better substrate for protein phosphatase 1.
•In muscle, insulin increases uptake of glucose so G6P increases, (a potent glycogen phosphorylase inhibitor) |
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Term
| Lysosomal degrading of glycogen |
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Definition
by alph(1>4)glucosidase, deficiency will make glycogen accumulate in vacuoles (Pompe disease)
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Term
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Definition
defect in enzyme for glycogen synthesis/degrading
accumulate in tissues or have abnormal structure, can be fatal to mild |
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Term
| Glycogen Synthesis/Degrading tightly regulated by... |
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Definition
1. glycogen synthae/glycogen phosphorylase allosterically controlled
2. paths of synthesis, degrading hormonally regulated |
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Term
| Allosteric regulation of glycogen synthesis/degrading |
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Definition
well fed state: glycog synthase activated by high G6P, glycog phosphorylase inhibited by high G6P & ATP
degrading in muscle by calcium binding calmodulin, activate phosphorylase kinase.
glycog phosphorylase active in muscle increases AMP (anorexia and ATP depletion events) |
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Term
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Definition
Ep signals needed for glucose/energy
Gs > AC > cAMP > PKA, phosphorylates inactive b form of phosphorylase kinase
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Term
| cAMP directed glycogen inhibition |
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Definition
Gs leads to AC then cAMP then PKA, phosphorylates and inactivates glycogen synthase.
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Term
| 4 things to promote glycogen synthesis in liver |
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Definition
G6P, Insulin (+synthase)
Glucose, ATP (- phosphorylase) |
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Term
| 3 things to promote glycogenolysis in liver |
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Definition
Glucagon
Epinephrine
Caffeine
(+ phosphorylase) > phosphorylation of phosphorylase= activation |
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