glycogen metabolism 2
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- what specific bond is associated with branching on a glycogen molecule?
- alpha-1,6-glycosidic bond
- branching on a glycogen molecule occurs at approximately every ______ glucose monomers.
- 8 to 14
- in the first step of glycogen synthesis, glucose-1-P goes to UDP-glucose via what enzyme and cofactor?
- UDP-glucose pyrophosphorylase and UTP
- are the 2 Phosphates on UDP-glucose both from UTP?
- No, one is from UTP and the other remains from glucose-1-P.
- what, self-glycosylating, protein forms the initial glucose monomer chain from which glycogen can be formed?
- Glycogenin
- what enzyme acts to add UDP-glucose to the growing glycogen chain?
- glycogen synthase
- is UDP-glucose added to the non-reducing or reducing end of the glycogen template?
- non-reducing end
- what action the the 'branching enzyme' perform? be specific
-
-a 7 segment section is transferred from the non-reducing endof a chain to the C6-hydroxyl group on the same or another glycogen molecule.
-every segment transferred comes from a chain at least 11 residues long.
-branching point must be at least 4 residues from all other branches - In regards to glycogen degredation, what are the yeilded percentages of glucose-1-P to free glucose?
- 90% G-1-P to 10% free glucose
- wat is the action of 'glycogen phosphorylase'?
-
-causes the cleavage of alpha-1,4-linked residues yeilding G-1-P + Gly(n-1).
-continues cleavage until at least 5 residues from a branching point. - what is the mechanism of action of the 'debranching enzyme'?
-
-first, the enzyme transfers the last three residues on the branch chain to the non-reducing end of another glycogen molecule.
-then, the enzyme cleaves the alpha-1,6-glycosidic linkage to yeild free glucose + debranched glycogen. - How many active sites does the 'debranching enzyme' have?
- 2 active sites
- what are the allosteric effectors of 'glycogen phosphorylase'? how do they effect the enzyme?
-
activator: AMP, (phosphorylation)
inhibitors: ATP, Glucose-6-P, free glucose. - what are the allosteric effectors of 'glycogen synthase'? how do they effect the enzyme?
-
activators: ATP, liver glucose, gucose-6-P.
inhibitor: (phosphorylation) - glucogon binds to a cell surface receptor protein which is a member of a group of proteins called, _____.
- G-proteins
- the G-protein receptor of glucagon activates what enzyme?
- adenylate cyclase
- adenylate cyclase aids in the synthesis of what molecule?
- cyclic-AMP
- what group of proteins does cAMP phosphorylate and activate?
- "cAMP dependant protein kinases"
- cAMP dependant protain kinases phosphorylate and activate what two enzymes?
- phosphorylase kinase and PPI-1 (phosphoprotein phosphatase inhibitor-1)
- 'phosphorylase kinase' phosphorylates what two enymes with what effect?
-
glycogen synthase (inactivates)
glycogen phosphorylase (activates) - what two effects do the actions of action of phsphorylase kinase have which together have an additive effect.
-
it activates glycogen degredation at the same tome as it inhibits gycogen synthesis.
-this ensures a unidirectional path. - Ca+ inds to what subunit of the phosphorylase kinase enzyme? what affect does this have?
-
binds to 'calmodulin' subunit. results in increased enzyme activity.
(binding of AMP also causes increased activity...) - what glucose transporter is activated by insulin? where is it present? how is it stored?
- GLUT-4. present in muscle and adipose tissue. stored in intracellular vesicles.
- what two effects does insulin binding to muscle cells have on the glucose transporter GLUT-4?
- stimulates its release from intracellular vesicles and also INCREASES its Vmax.
- what effect does insulin binding have on 'phosphodiesterase'? what does this enzyme do?
- activates phosphodiesterase which in turn degrades cAMP.
- what effect does insulin have on 'phosphoprotein phosphatase-1 (PP-1)? what does this enzyme do?
- activates the enzyme which leads to the Dephosphorylation of: phosphorylase kinase, glycogen synthase, glycogen phosphorylase and PPI-1
- which enzyme of gluconeogenesis is effected by insulin? how?
- insulin leads to the inactivation of PEPCK.