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31 Cards in this Set

  • Front
  • Back
what is the structure of glycogen?
alpha-1,4-linkages w/ alpha-1,6-linkage brr.
Within what structures is glycogen synthesized?
Liver & Muscle
what is the fn of glycogen in the liver?
acts as buffer
how long do glycogen stores last in the liver?
what enzyme phosphorylates glucose in skeletal muscle?
Hexokinase (low Km)
What enzyme does m. lack?
G-6-Pase phosphatase
what efect does glycogen synthesis have on glucose levels?
Decreases glucose in the blood
During fasting what is the role og glycogenesis, gluconeogenesis?
glycogenesis for the first 24 hrs, gluconeogenesis takes over after that!
Glucogen synthesis- Describe the pathway starting from glucose.
Glucose=>G-6-P => G-1-P => UDP Glucose =>Glycogen
What enzyme is required to initiate glycogen synthesis? what is its fn?
glycogen synthase; adds alpha-1,4-linkages.
If glycogen synthase is absent what happens?
Glycogenin attached to TYR residue steps in
In what state is glycogen stnthase active?
non-phosphorylated state
on which ends are chains of the alpha-1,4 and alpha-1,6-linkages added? Which enzyme is used to elongate?
non-reducing ends via glycogen synthase making alpha-1,4-bonds. Further elongation results in alpha-1,6 bonds.
How is UDP reconverted to UTP, via what enzyme?
UDP + ATP => UTP + ADP via nucleoside diphosphate kinase.
With which enzymes are the alpha-1,6-linkage brr. creates?
Branching enzyme or glucosyl-alpha-1,6-transferase
What are the principle products of glycogen degredation?
G-1-P and a shortened (n-1) glycogen polymer
What is the most abundant type of bond and what enzyme breaks this bond?
alpha-1,4-bonds and glycogen phosphorylase
What are the 4 purposes of G6P in the liver?
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
What occurs when G-6-Pase is absent?
Glycogenosis I or Von Gierke's Disease
What is Von Gierke's Disease?
Insufficient amt of glucose are produced from the hydrolysis of G6P.
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.
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.
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.
What are the two levels of regulation of glycogen metabolism?
allosteric means & hormonal mechanisms
What are the major allosteric activators of glycogen breakdown?
Calcium, 5'-AMP (indicator of low energy charge)
What are the major allosteric inhibitors of glycogen breakdown?
Free glucose, G-6-P, ATP
How is glycogen degredation activated in the muscle?
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.
What are the hormones involved in the activation/inhibition os glycogen synthase or phosphorylase?
Glucagon (liver) and Epinephrine (muscle & liver)
What is their fn?
Activate G-Protein which in turn raises c-AMP levels.
What is the fn of epinephrine?
Glycogen breakdown
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.