Glycogen Metabolism Flashcards
How is glycogen synthesis favored
by insulin - in both liver and muscle
What does the liver do with glycogen
releases as free glucose in flight or fight situation
what does the muscle do with glycogen?
stores it for energy metabolism
what regulates glycogen degradation in the liver/
hormones - during fasting or low insulin/glucagon ratio - glucose is released into the blood
what is glycogen degradation linked to in skeletal muscle
muscle contraction - independent of hormones (you don’t wanna wait for hormones to have a contraction!) - G-6-P is used in glycolysis
what stimulates glycogenolysis in liver and muscle?
epinepherine = hormone
what takes place at the same time at low insulin levels?
gluconeogensis and glycogen degradation
what happens at the same time when the muscle needs ATP
glycogen degradaiton and glycolysis
when does the muscles glycogen store deplete?
not during fasting - during exercise!
where is glycogen mainly found in the body?
largest amount = skeletal muscle
highest concentration = liver
what can glycogen storage diseases affect?
liver only, or muscle only or BOTH
what is the purpose of glycogen metabolism (2)
synthesis of glycogen when G-6-P is abundant - high insulin in liver and muscle
degradatino of glycogen when G-6-P is needed - low insulin in liver/muscle contraction in muscle
in what cellular compartment is glycogen degraded and metabolized?
in the cytosol
glycogen is stored in cytosolic granules of liver and muscle
what is special about glycogen metabolism?
many enzymes can act at the same time on glycogen because of the branched structure - tightly regulated thouhg (glycogen phophorylases vs. glycogen synthase)
what is glycogenic?
core protein surrounded by branches
what do both gylcogen syntehsis and glycogen degradation use?
glucose 6-P and Glucose-1-P - reversibly formed by phosphoglucomutase
what is the highly activated form of glucose used for synthesis of glycogen? how is it made?
UDP-glucose
made from glucose-1-P + UTP
what is glycogen syntheases primer needed to link UDP-glucose together
some branched glyogen chains that are not totally degraded - then it makes the alpha 1,4 bonds
when alll the glycogen chains are degraded, what do we need?
glycogenin protein
what does glycogenin do?
self-glucosylating enzyme (similar to ser and thr) uses UDP-glucose and add like 8 glucose units to its own try residue —EXCEPTION
what is the point of having so many branches?
they improve solubility of glycogen
allow for accelerated rates of glycogen synthesis or degradation
what does 4:6 transferase do?
removes a chain of about 8 glucosyl residues from the nonreducing end (by cleaving hte alpha 1-4 bond) and attached it to a non-temrinal glucosyl residue by an alpha 1-6 linkage
when do you want glycogen sythase to be active?
insulin ruling
what coenzyme does phosphorolytical cleavage of glycogen to G-1-P need>
pyridoxal phosphate (PLP) fromed from vitamin B6
what is pyridoxal phosphate usually used for?
amino acid metabolism - this is an exception
why is it important to get to a glycogen store in muscle?
it saves an ATP because you don’t need to convert glucose to G-6-P, you just have G-1-P and you can change it to G-6-P without using an ATP
in both liver and muscle, how is glycogen synthease activated?
by glucose-6-P
what inhibits glycogen degradation (glycogen phosphorylase) in muscle and liver?
glucose-6-P
ATP
what inhibits glycogen degradation in liver only?
glucose
what activates degradation in muscle only?
AMP (generated by muscle contraction)
what is limit dextrin?
intermediate in glycogen degradation which is a substrate for debranching enzymes
what does 4:4 transferase do
leads from limit dextrin to longer branches
what does 1:6 glucosidase do?
cleaves the alpha 1-6 bond at the branch point and generates 1 free glucose molecule
what does gylcogen degradation generate?
G-1-P and some free glucose
what can protein kinase A only phosphorylate?
glycogen phosphorylase kinase
what is glycogen phospohrylase kinase?
the enzyme which phosphorylates and activates glycogen phosphorylase b which makes it a
what does glyocgen phosphorylase kinase have
calcium for allosteric activation and calmodulin
what does AMP allosterically activate?
glycogen phophorylase
what does glycogen synthase do (in general)
takes 2 UDP-glucose and smushes them together! - but it needs a primer to do that!
