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31 Cards in this Set
- Front
- Back
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what is the structure of glycogen?
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alpha-1,4-linkages w/ alpha-1,6-linkage brr.
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Within what structures is glycogen synthesized?
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Liver & Muscle
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what is the fn of glycogen in the liver?
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acts as buffer
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how long do glycogen stores last in the liver?
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12-24hrs
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what enzyme phosphorylates glucose in skeletal muscle?
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Hexokinase (low Km)
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What enzyme does m. lack?
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G-6-Pase phosphatase
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what efect does glycogen synthesis have on glucose levels?
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Decreases glucose in the blood
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During fasting what is the role og glycogenesis, gluconeogenesis?
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glycogenesis for the first 24 hrs, gluconeogenesis takes over after that!
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Glucogen synthesis- Describe the pathway starting from glucose.
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Glucose=>G-6-P => G-1-P => UDP Glucose =>Glycogen
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What enzyme is required to initiate glycogen synthesis? what is its fn?
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glycogen synthase; adds alpha-1,4-linkages.
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If glycogen synthase is absent what happens?
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Glycogenin attached to TYR residue steps in
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In what state is glycogen stnthase active?
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non-phosphorylated state
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on which ends are chains of the alpha-1,4 and alpha-1,6-linkages added? Which enzyme is used to elongate?
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non-reducing ends via glycogen synthase making alpha-1,4-bonds. Further elongation results in alpha-1,6 bonds.
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How is UDP reconverted to UTP, via what enzyme?
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UDP + ATP => UTP + ADP via nucleoside diphosphate kinase.
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With which enzymes are the alpha-1,6-linkage brr. creates?
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Branching enzyme or glucosyl-alpha-1,6-transferase
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What are the principle products of glycogen degredation?
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G-1-P and a shortened (n-1) glycogen polymer
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What is the most abundant type of bond and what enzyme breaks this bond?
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alpha-1,4-bonds and glycogen phosphorylase
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What are the 4 purposes of G6P in the liver?
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1. conversion back to G1P
2. use in glycolysis 3. clevage to form free glucose and release from the cell into circulation 4. The hexose monophosphate pathway |
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What occurs when G-6-Pase is absent?
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Glycogenosis I or Von Gierke's Disease
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What is Von Gierke's Disease?
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Insufficient amt of glucose are produced from the hydrolysis of G6P.
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Where is Von Gierke's disease generalized?
What is the primary symptom in infants? What are other symptoms? |
In liver, heart and muscle
Enlarged liver Normal glycogen structure, massie cardiomegaly, normal blood sugar levels, excessive glcogen conc., early death from heart failure. |
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McArdle's Syndrome (Type V) results from...
What are the clinical features? Do patients usually die? |
deficiency of glycogen phosphorylase.
No rise in lactate during vigorus exercise, cramping after exercise, high level of glycogen with normal structure in muscle. Good prognosis, not resulting in death. |
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Pompe's Disease (Type II) is a deficiency in...
Where can this be found? Describe the severity in child vs adult |
Acid alpha-1,4 glucosidase
Can be found in any tissue that synthesizes glycogen Children have severe diseae whereas adults have a mild case. |
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What are the two levels of regulation of glycogen metabolism?
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allosteric means & hormonal mechanisms
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What are the major allosteric activators of glycogen breakdown?
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Calcium, 5'-AMP (indicator of low energy charge)
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What are the major allosteric inhibitors of glycogen breakdown?
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Free glucose, G-6-P, ATP
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How is glycogen degredation activated in the muscle?
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Calcium binds to Calmodulin. This complex activates phosphorylase kinase. When muscle is inactive the Calciu returns to th Sarcoplasmic Reticulum and phosphorylase kinase become inactive.
Note: This does not need cAMP to phosphorylate the kinase. |
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What are the hormones involved in the activation/inhibition os glycogen synthase or phosphorylase?
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Glucagon (liver) and Epinephrine (muscle & liver)
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What is their fn?
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Activate G-Protein which in turn raises c-AMP levels.
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What is the fn of epinephrine?
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Glycogen breakdown
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GLUCOKINASE -VS- HEXOKINASE:
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Glucokinase has a higher km! It has a lower than normal affinity for trapping glucose in the liver.
This means it has a higher saturation point and a higher capacity for trapping glucose via the kinase activity. This allows the liver to act as a buffer in taking up extra blood glucose. Hexokinase is inhibited by its product, G-6-P, whereas glucokinase is not. This again allows the liver to take up maximal amounts of glucose. Glucokinase is inhibited by F-6-P and F-1-P, whereas hexokinase is not. |
