glycogen synthesis Flashcards
what is the function of liver glycogen?
used to maintain glucose levels in the blood
stores glucose when glucose levels are too high and releases glucose when glucose levels are too low
what is the function of muscle glycogen?
maintain muscle during bursts of activity
local energy store to allow muscles to do their first burst of energy
what is the advantage of glycogen being less osmotically active than glucose?
can be stored
why can liver glycogen be used to make glucose and not muscle glycogen?
liver has an enzyme which isn’t found in muscle tissue which allows glucose-6-phosphate to be dephosphorylated back to glucose
in what ways can muscle glycogen be used to make ATP?
anaerobic glycolysis
aerobic metabolism
what is glycogenic?
a protein primer
which bonds join molecules of glucose together in glycogen?
carbon 1-4 links
which end of glycogen is extended?
carbon 4 end
which bond is needed to form a branch in glycogen?
carbon 1-6
what enzyme is needed to form a glycogen branch?
glycogen branching enzyme
after how many residues is a branch found in the main chain of glycogen?
every 12-14 residues
what is the advantage of branches?
make glycogen and its energy easily accessible
helps solubility inside cell
explain the process of glycogen synthesis
glucose-6-phosphate –> glucose-1-phosphate
UTP used to make UDP-glucose and PPi
Glycogen synthase removes UDP and adds glycogen onto the glycogen chain to extend it, with glycogenin as the primer
how is glucose-6-phosphate converted into glucose-1-phosphate?
moving the phosphate from carbon 6 to carbon 1
what is the energy from PPi –> 2Pi used for?
pushing UDP-glucose–> glycogen reaction to the right
what effect does insulin have on glycogen synthase and glycogen?
insulin increases glucose storage into glycogen
glycogen synthase is active
what effect does glucagon have on glycogen synthase and glycogen?
glucagon releases glucose into the blood
glycogen synthase is inactive
how is glycogen synthase affected when it’s phosphorylated/dephosphorylated?
Phosphorylated – inactive
Dephosphorylated – active
how does insulin dephosphorylate glycogen synthase?
activating protein phosphatase-1
how is glycogen synthase phosphorylated?
protein kinase A and phosphorylase kinase
what controls the phosphorylation of glycogen synthase?
cAMP
glucagon (liver)
adrenaline (muscle)
what is glycogenolysis?
breakdown of glycogen
what stimulates the breakdown of liver glycogen?
glucagon via phosphorylation of glycogen phosphorylase
what enzyme breaks down glycogen?
glycogen phosphorylase
what effect does phosphorylation and dephosphorylation have on glycogen phosphorylase?
Phosphorylated – active
Dephosphorylated – inactive
what enzyme converts glucose-6-phosphate to glucose?
glucose-6-phosphatase
what does muscle glycogen breakdown feed into?
glycolysis and energy production in that cell only
under anaerobic conditions, what does glycolysis produce?
lactate
describe the control of glycogen breakdown
Adrenaline + Glucagon activates adenylyl cyclase to convert ATP to cAMP
cAMP activates Protein Kinase A (PKA) to convert ATP to ADP.
phosphorylase kinase b into phosphorylase kinase a which then converts ATP to ADP
used to convert glycogen phosphorylase b to glycogen phosphorylase a
Glycogen phosphorylase cleaves glycogen to produce glucose-1-phosphate
then converted to glucose-6-phosphate
what inheritance pattern are all glycogen storage diseases?
autosomal recessive
what is the deficiency and consequence of type 1 - von Gierke’s?
glucose-6-phosphatase deficiency
leads to hypoglycaemia and lacticacidemina
what is the deficiency and consequence of type 2 (Pompe’s)?
deficiency in lysosomal glycogen breakdown
leads to heart failure
what is the deficiency and consequence of type 3 (Cori’s)?
deficiency in debranching enzyme
leads to hypoglycaemia
what is the deficiency and consequence of type 4 (Andersen’s)?
deficiency in branching enzyme
unknown consequence
what is the deficiency and consequence of type 5 (McArdle’s)?
deficiency in muscle phosphorylase
leads to exercise-induced cramps and fatigue
what is the deficiency and consequence of type 6 (Her’s)
deficiency in liver phosphorylase
leads to hypoglycemia
