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Flashcards in Glycogen Deck (29)
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What are the major tissue types where glycogen is produced?

Liver and Muscle.


Which tissue directly contributes to blood glucose levels?



Which tissue is insulin dependent for glucose uptake? Independent?

Dependent: Adipose and Muscle
Independent: Liver, Brain.


Describe the events in insulin release after a meal and the cellular response.

1. Insulin binds to receptor in cell membrane
2. receptor promotes recruitment of vesicles containing glucose transporters to the cell membrane
3. Vesicles fuse to membrane, increasing amount of glucose transporters in the membrane.


What is activated in order to assist the vesicles containing glucose transporters to move towards the cell membrane?

Protein Kinase B (PKB)


When insulin levels are low, how do muscle cells circumvent this problem in order to recruit glucose transporters to the membrane?

Use ATP to up AMP levels, which stimulates AMP-kinase and promotes the translocation of the transporters.


How is exercising in diabetes patients beneficial?

Because muscles can circumvent the lack of insulin and continue to transport glucose.


What is the common first step in all glucose related pathways? Results in what kind of molecule?

The phosphorylation of glucose to give Glucose 6-P. This is a highly polar charged molecule that cant escape the cell.


What is the first reaction formula in glucose pathway? Catalysts?

Glucose + ATP= Glucose 6-P and ADP. Catalyzed y Hexokinase and Glucokinase.


What are the characteristics of Hexokinase (tissue, Levels, Affinity, Inhibited)?

1. In general tissue
2. Constitutive enzyme
3. Low Km (High affinity for glucose)
4. Inhibited by product


What are the characteristics of Glucokinase (tissue, Levels, Affinity, Inhibited)?

1. In liver only
2. Induced Enzyme
3. high Km (low affinity for glucose)
4. Not inhibited by product


How is glucokinase regulated? What two molecules stimulate its release?

In a fasting state, Glucokinase is bound to GKRP and inactive in the nucleus of the cell. Glucose and Fructose1-P can stimulate its release from GKRP.


What is gluconeogenesis?

The process of making Pyruvate into Glucose during low levels of blood glucose.


Describe the process of Glycogenesis from glucose. What type of bonds is the result?

1. Glucose+ ATP= Glucose 6-P
2. Glucose 6-P-->Glucose 1-P
3. UTP + Glucose 1-P= UDP-Glucose and 2Pi
4. UDPG with Glycogen Synthase-->UDP and transfers Glucose to the non-reducing end of a glycogen primer.
alpha-1,4 bonds are the result in the chain.


How is UTP regenerated?

ATP is used to create UTP from UDP.


How many ATP is used per glucose molecule in glycogenesis?



What is Glycogenin? What is it used for? What type of bonds?

Is a dimer with tyrosine residues arranged head to toe. It transfers glucose from UDP-G to create glycogen chain when a glycogen fragment is absent to accept the glucose. a-1,4 bonds


How are branches formed in glycogen formation?

Branching enzymes transfer a group of 5-8 glucoses in the chain to a more interior side and links it with a a-1,6 bond.


How is glycogenolysis achieved in a non-branching glycogen chain?

Glycogen Phosphorylase cleaves a glucose molecule from the non-reducing ends of the glycogen chain. It then phosphorylates that glucose created Glucose 1-P.


How is glcogenolysis achieved at a glycogen branching point?

De-branching enzyme uses transferase to transfers a group of 3 glucoses to an a jointing chain. It then uses glucosidase to hydrolyze the remaining a-1,4 bond, freeing that glucose.


What enzyme will convert Glucose 6-P into glucose in the liver only?

glucose 6-Phosphatase


What does glycogen phosphorylase do? Glycogen Synthase? When are they active?

1. Phosphorylase: Converts glycogen into Glucose1-P, active during fasting state.
2. Synthase: Adds glucose onto growing glycogen chains. Active during well fed state.


Phosphorylated Glycogen synthase is active or inactive? P-Glycogen phosphorylase?

Phosphorylase-P= Active


How is Glycogen Phosphorylase phosphorylated? Un-P?

Phosphorylase kinase phosphorylates (activates).
Phosphotase removes P (Inactivates).


What three kinases can Glycogen Synthase be Phosphorylated by?

1. Protein Kinase A (PKA)
2. Phosphroylase Kinase
3. GSK-3


What 2 hormones are activators of glycogenolysis? Characteristics (origin, tissue)?

1. Glucagon: From alpha cells in pancreas, In liver only
2. Epinephrine: Secreted by adrenal medulla during stress, trauma, physical activity. In muscle and liver.


Describe the activation of Protein Kinase A pathway.

1. Glucogon or epi binds to G-protein receptor
2. Adenylyl cyclase converts ATP to cAMP
3. cAMP activates PKA
4. PKA activates phosphorylase, de-activates synthase


What does insulin do to Adenylate cyclase activity?

It blocks its activity. This causes phosphorylation activity to cease.


What is the Insulin Glucogon ration equation?

Blood Glucose=Rate of Supply/Rate of Removal=Glucagon,Epi,Cortisol,CH,TH/Insulin