Exam 3 Lecture #2: Glycogen Metabolism Flashcards
Glycogen is composed of mainly glycosyl linkages, mostly linked by ______ linkages.
Branches arise frequently from ______ linkages.
Glycogen is composed of mainly glycosyl linkages, mostly linked by alpha 1,4 linkages,
Branches arise frequently from alpha 1,6 linkages.
Draw the diagram on what happens to liver glycogen levels between meals and during the nocturnal fast.
Explain Glycogen Synthesis in the Liver:
_________ is the key enzyme which adds glucose-1-P to the growing glycogen chain
The liver can store about ______ of glycogen.
What happens when that limit is reached?
Glycogen Synthesis in the Liver:
Glycogen Synthase is the key enzyme which adds glucose-1-P to the growing glycogen chain.
The liver can store about 100g of glycogen.
Once that amount is stored, excess glucose is redirected towards fatty acid synthesis.
Explain glycogen degradation in the liver:
________ is the key enzyme involved in removing glucose from glycogen.
The liver expresses the enzyme ___________
Glycogen Degradation in the Liver:
Glycogen Phosphorylase is the key enzyme involved in removing glucose from glycogen.
Liver expresses the enzyme glucose-6-phosphatase.
Which enzyme does the liver express but muslce does not express in terms of glycogen degradation?
Muscle does not express glucose 6 phosphatase.
Muscle Glycogen Synthesis and Degradation:
Muscle can store up to ______ of glycogen.
Excess muscle glucose converted to _______
Muscle can store up to 400g of glycogen.
Excess muscle glucose converted to Fatty Acids and stored as triacylglycerols.
When does muscle glycogen get used?
Muscle glycogen NOT used to increase plasma glucose levels during hypoglycemia.
Degradation of muscle glycogen stimulated by EPI or muscle contraction to be used during exercise/fight or flight.
Glucose transporter in liver vs glucose transporter in muscle
GLUT 2: liver
GLUT 4: muscle
Explain the sequence of energy sources during exercise? Aka what gets used first, second, etc
- ATP and creatine phosphate (first few seconds)
- Anaerobic Glycolysis: muscle glycogen (minutes 1-5)
- Aerobic Oxidation (muscle glycogen, plasma glucose, liver glycogen)
- Aerobic Oxidation (plasma FFA, adipose tissue TAGs)
What energy currency is used during glycogen formation?
Draw the triangle connecting glucose-6-P to glycogen formation and degradation
UDP is used during glycogen formation
What are the two enzymes that Glycogen Synthesis requires?
Glycogen Synthesis Requires:
- Glycogen Synthase : adds glucosyl units in an alpha 1, 4 linkage
- Branching Enzyme: adds glucosyl units in an alpha 1, 6 linkage
How many glucose units are between branch points?
10-14 glucosyl units in between branch points in glycogen
Which protein serves as a primer for glycogen synthesis?
Glycogenin serves as a primer for glycogen synthesis
What enzymes are required for Glycogen Degradation?
Glycogen Degradation Requires:
- Glycogen Phosphorylase (removes glucosyl units from alpha 1, 4 linkage)
- Debranching Enzyme (transferase and alpha 1,6 glucosidase)
- Additional Kinases are used to activate the glycogen phosphorylase
What are the three second messenger systems that play a role in the regulation of glycogen metabolism?
Regulation of Glycogen Metabolism:
Second Messenger Systems:
- cAMP
- PI, IP3
- Calcium
How to the three messenger systems activate glycogen breakdown?
Three second messenger systems, i.e. cAMP, PI and Ca2+ activate glycogen phosphorylase by activating phosphorylase kinase, which phosphorlyates and activates glycogen phosphorylase….. leading to glycogen degradation
Glycogen phosphorylase is “active” in which form?
Glycogen phosphorylase is active when it gets phosphorylated by the kinase (this state is also known as phosphorylase a)
think “a” means activated
What does cAMP do to help promote glycogen degradation?
cAMP activates protein kinase A, which in turn P/activates the phosphorylase kinase, which then in turn also activates the glycogen phosphorylase.
cAMP also inhibts the phosphoprotein phosphatase
How does glucagon promote glycogen degradation?
Glucagon promotes the activation of glycogen phosphorylase by activating the kinase, AND by phosphorylating/inhibiting the phosphatase
How does calcium play a role in regulation?
Calcium is necessary for the phosphorylase kinase to work
Explain GSD V and VI
GSD V and VI: Defeciency of Glycogen Phosphorylase…the pt will not be able to utilize glycogen, and therefore during the fasting state the pt will have increased ketone bodies in the blood
(can’t use glycogen so you mobilize beta oxidation of fatty acids)
Insulin inhibits glycogen degradation by____
Insulin inhibits glycogen phosphorylation by causing the enzyme to be dephosphorylated and inactivated.
What are the effects of AMP, Glucose and ATP on glycogen phosphorylase?
High levels of AMP (like during exercise) will cause AMP to directly bind to the “b”/inactivated form of the phosphorylase, resulting in a conformational change to make the phosphorylase change to an active form, overriding the negative effect of ATP.
Similarly, when glucose and ATP levels are high they can find to the active/”a” form and cause it to become inactive.
Insulin promotes glocogen storage or degradation?
How does it do that
Insulin promotes glycogen storage
Insulin inhibits glycogen phosphorylase by causing the enzyme to be dephosphorylated and therefore inactivated
