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23 Cards in this Set

  • Front
  • Back
Glycogen structure
Large branched polymer consisting of D glucose residues
Linkages of glycogen
Alpha 1,4 except branch points where its alpha 1,6
Precursor for glycogen synthesis
UDP glucose
Glucose enters cell and is phosphorylated to _ by enzyme _
Hexokinase (glucokinase in liver)
Enzyme that converts G-6-P to G-1-P
Synthesis of UDP glucose
Glucose enters cell and is phosphorylated quickly to G-6-P in order to trap it in the cell. G-6-P is converted to G-1-P. G-1-P reacts with UTP forming UDP GLUCOSE which is catalyzed by UDP glucose pyrophosphorylase and pyrophosphate is kicked out
Key regulatory enzyme for glycogen synthesis
Glycogen synthase - transfers glucose residues from UDP glucose to nonreducing ends of glycogen primer - UDP is released and is reconverted to UTP
When does branching take place in glycogen
When chain contains 11 or more glucose residues, an oligomer (6-8 residues ) is removed from nonreducing end and reattached via alpha 1,6 linkage as a branch
Branching glycogen enzyme
Glucosyl 4:6 transferase - breaks alpha 1,4 bond and makes alpha 1,6 bond
How is glycogen degraded
Glycogen phosphorylase - enzyme for glycogen degradation - removes glucose residues from non reducing end of glycogen, it cleaves alpha 1,4 bonds to make G-1-P
How are branches removed in glycogen
Debranching enzyme - glucosyl 4:4 transferase and alpha 1,6 glucosidase
Phosphorylase can only act till its 4 glucose residues before the branch point, three of those are removed by transferase 4:4 and reattached to another chain's nonreducing end - breaks alpha 1,4 and creates another alpha 1,4. Last glucose residue is hydrolyzed by 1,6 glucosidase which breaks alpha 1,6 bond and makes free glucose
Which two hormones stimulate glycogen degradation
Glucagon -acts on liver cells
Epinephrine - acts on liver and muscle cells
Describe how glycogen degradation is stimulated
-Glucagon and epi via G proteins activate adenylate cyclase which converts ATP to cAMP
-cAMP activates PKA
-PKA phosphorylates glycogen synthase causing it to be less active and thus reducing glycogen synthesis
-PKA phosphorylates phosphorylase kinase
-Phosphorylase kinase phosphorylates glycogen phosphorylase b (inactive form) and turns it into glycogen phosphorylase a (active form)
-Phosphorylase a cleaves glucose residues from nonreducing end of glycogen and produces G-1-P which in liver can be converted back to free glucose
What stimulates glycogen breakdown in muscle
AMP and Ca
-Phosphorylase b is activated by rise in AMP during muscle contraction
-Phosphorylase kinase is activated by Ca binding to calmodulin
Which hormone stimulates synthesis of glycogen
INSULIN - elevated after meal and stimulates synthesis of glycogen in liver and muscle
Describe hormonal regulation of glycogen synthesis
Dephosphorylation of phosphorylase kinase and phosphorylase a causes enzymes to be deactivated, insulin causes activation of phosphatases that dephosphorylate these enzymes, it also activates glycogen synthase that promotes glycogen synthesis
Insulin stimulates transport of glucose to _
Fat and muscle
Type I glycogen storage disease
Von Gierke disease
Defficiency of GLUCOSE-6-PHOSPHATASE in liver, intestine and kidney.
-Hypoglycemia - liver cant release glucose
-Lactic acidemia - cant process lactose normally and also increased glycolysis
-Increased uric acid
Type II glycogen storage disease
Pompe's disease - accumulation of glycogen in any tissue
Defficiency of alpha 1,4 glucosidase which normally breaks down glycogen in lysosomes
Symptoms - massive enlargement of heart and death before 30 (glycogen in cardiac muscle)
Type III glycogne storages disease
Coris disease - mild glycogen accumulation due to defficiency in DEBRANCHING ENZYME
Hepatomegaly can occur, not severe disease
Type V glycogen storage disease
McArdles disease - muscle glycogen phosphorylase defficiency
Coris vs Andersons disease
Andersons - branching enzyme
Coris - debranching enzyme
Type IV glycogen storage disease