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23 Cards in this Set
- Front
- Back
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Glycogen structure
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Large branched polymer consisting of D glucose residues
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Linkages of glycogen
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Alpha 1,4 except branch points where its alpha 1,6
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Precursor for glycogen synthesis
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UDP glucose
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Glucose enters cell and is phosphorylated to _ by enzyme _
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Glucose-6-P
Hexokinase (glucokinase in liver) |
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Enzyme that converts G-6-P to G-1-P
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Phosphoglucomutase
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Synthesis of UDP glucose
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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
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Key regulatory enzyme for glycogen synthesis
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Glycogen synthase - transfers glucose residues from UDP glucose to nonreducing ends of glycogen primer - UDP is released and is reconverted to UTP
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When does branching take place in glycogen
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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
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Branching glycogen enzyme
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Glucosyl 4:6 transferase - breaks alpha 1,4 bond and makes alpha 1,6 bond
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How is glycogen degraded
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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
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How are branches removed in glycogen
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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 |
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Which two hormones stimulate glycogen degradation
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Glucagon -acts on liver cells
Epinephrine - acts on liver and muscle cells |
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Describe how glycogen degradation is stimulated
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-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 |
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What stimulates glycogen breakdown in muscle
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AMP and Ca
-Phosphorylase b is activated by rise in AMP during muscle contraction -Phosphorylase kinase is activated by Ca binding to calmodulin |
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Which hormone stimulates synthesis of glycogen
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INSULIN - elevated after meal and stimulates synthesis of glycogen in liver and muscle
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Describe hormonal regulation of glycogen synthesis
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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
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Insulin stimulates transport of glucose to _
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Fat and muscle
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Type I glycogen storage disease
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Von Gierke disease
Defficiency of GLUCOSE-6-PHOSPHATASE in liver, intestine and kidney. Symptoms: -Hypoglycemia - liver cant release glucose -Lactic acidemia - cant process lactose normally and also increased glycolysis -Increased uric acid |
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Type II glycogen storage disease
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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) |
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Type III glycogne storages disease
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Coris disease - mild glycogen accumulation due to defficiency in DEBRANCHING ENZYME
Hepatomegaly can occur, not severe disease |
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Type V glycogen storage disease
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McArdles disease - muscle glycogen phosphorylase defficiency
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Coris vs Andersons disease
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ABCD
Andersons - branching enzyme Coris - debranching enzyme |
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Type IV glycogen storage disease
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Lack BRANCHING ENZYME
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