Metabolism 5 Flashcards
Describe glycogen.
Glycogen, a Highly Branched Storage Form of Glucose, Is Required as a Ready Source of Energy.
Glycogen is composed of
glycosyl residues, mostly linked by alpha-1, 4 glycosidic linkage.
Branches arise from frequently
alpha-1, 6 glycosidic linkage.
How does hepatic glycogen concentration change throughout the day (in regards to meals).
Hepatic glycogen concentration increases after meals and declines between meals.
graph p 4
Glycogen is stored in muscle and liver for quite different reasons. Explain.
Glycogen is stored in muscle and liver for quite different reasons. Muscle glycogen is a
fuel reserved for the production of ATP within that tissue. Liver glycogen is a glucose reserve for the maintenance of blood glucose concentration.
Describe glycogen in the liver. What enzyme is key to adding glucose 1-P to growing glycogen chains?
(How does blood glucose coming into liver get converted to liver glycogen and back)?
How much glycogen can the liver store? What happens when that capacity is reached?
What is the key enzyme needed to remove glucose moieties from glycogen?
What enzyme is crucial to allowing glucose from liver glycogen to contribute to blood glucose?
- glycogen synthase is the key enzyme which adds glucose 1-P to growing glycogen chains
(glucose from cytoplasm/blood…to glucose-6-P, then glucose-1-P to liver glycogen… and back to 1-p then 6-P)
- the liver can store about 100g of glycogen. Once this amount is stored, excess glucose is redirected toward FA synthesis.
- glycogen phosphorylase is the key enzyme involved in removing glucose moieties from glycogen
- the liver expresses glucose-6-phosphatase. Thus glucose from liver glycogen can directly contribute to blood glucose levels.
p5
How is muscle glycogen used?
Does it contribute to blood glucose in times of hypoglycemia?
When is muscle glycogen mobilized?
Does muscle glycogen express glucose-6-phosphatase? Explain implications.
How much glycogen can muscle store? What is happens when capacity is reached?
Muscle glycogen is not used to increase blood glucose in times of hypoglycemia. Muscle glycogen is mobilized during exercise. Because muscle does not express glucose-6-phosphatase, glucose-6-phosphate cannot leave the cell, instead it it used for ATP production.
Muscle can store about 400g of glycogen. Excessive glucose can be converted to FAs and stored as TGs.
glucose from cytoplasm…glucose-6-P to glucose-1-P then to muscle glycogen..glycogen back to 1-P and 6-P then undergoes glycolysis.
Describe/draw the synthesis and breakdown of hepatic and muscle glycogen.
Slide 7, p 6
Describe/draw the synthesis of muscle glycogen and breakdown of muscle glycogen during exercise.
p 6
GLUT4 bc muscle
What are the sources of energy during exercise? Which are used up first? Which is most sustainable?
(Draw).
ATP and creatine phosphate- used up in minutes
anaerobic glycolysis, muscle glycogen (5 min)
at 3 minutes aerobic oxidation, muscle glycogen, plasma glucose, liver glycogen… starts to drop off at about 3 hours
at 4 min aerobic oxidation/plasma FFA and adipose tissue triglycerides slowly/steadily rises, peaks at 1.5 hours and levels off.
See slide 9, or p 7
Show/draw a branching diagram of glycogen synthesis and degradation.
Describe what enzymes it requires.
Slide 10, p 8
Glycogen synthesis requires an enzyme (glycogen synthase) that adds
glucosyl units in an alpha-1,4 linkage. It also requires a branching enzyme.
Glycogen degradation requires an enzyme (glycogen phosphorylase)
that removes glucosyl units from an alpha-1,4 linkage and a
debranching enzyme. The debranching enzyme has two activities: transferase & alpha-1,6-glucosidase.
slide 12, p 9
What is glycogenin? Describe its function.
A polypeptide of 332 amino acids called Glycogenin serves as a primer for glycogen synthesis.
Are glucose/glycogen osmotically active?
Glucose is osmotically active,
whereas glycogen is not.
Describe the regulation of glycogen phosphorylase activity by multiple second messenger pathways.
Describe the role of AMP, Ca, calmodulin, insulin.
p 10, 11
AMP: The b form of muscle glycogen phosphorylase can be allosterically activated by AMP.
Ca2+ can activate phosphorylase kinase via binding to calmodulin, a subunit of this enzyme.
Insulin inhibits glycogen phosphorylase by activating phosphoprotein phosphatase; the latter enzyme dephosphorylates glycogen phosphorylase.
Describe the regulation of glycogen synthase by covalent modification.
Phosphorylation converts
glycogen synthase from its active alpha form to its inactive beta form.
Describe role of insulin on glycogen synthase.
Insulin activates glycogen synthase by activating phosphoprotein phosphatase; the latter enzyme dephosphorylates glycogen synthase.
Insulin inhibits glycogen phosphorylase by activating phosphoprotein
phosphatase; the latter enzyme dephosphorylates glycogen phosphorylase.
How is the b form of glycogen synthase activated?
Glucose 6-phosphate: The b form of glycogen synthase can be allosterically activated
by glucose 6-phosphate.
