BGM1002/L25 Glycogen Metabolism Flashcards
How many residues are between each branch point in glycogen?
10
Why is glucose converted to glycogen? (2)
Renal loss
Osmotic pressure
Why is glycogen branched?
Facilitates fast mobilisation
Where are the 2 main sites of glycogen storage?
Liver and muscle
Which is the largest glycogen store in the body?
Muscle
What percentage weight of muscle is glycogen?
2%
What is glucose released as in muscle?
Glucose-6-phosphate (just for muscle)
Why can’t glucose escape muscle cells?
Muscle lacks the enzyme to remove final phosphate group
What percentage by weight of glycogen is the liver?
10%
How many kJ/g is glycogen?
17
How many kJ/g is fat?
37kJ/g
Why does the body favour fat as an energy source?
It stores energy more efficiently
How many steps are there to glycogenesis?
3
Name the 4 main molecules in glycogenesis.
Glucose-6-phosphate
Glucose-1-phosphate
UDP-glucose
Glycogen
Name step 1 of glycogenesis.
Diversion
Glucose-6-phosphate -> glucose-1-phosphate
What enzyme is involved in diversion (step 1) of glycogenesis?
Phosphoglucomutase
Name step 2 of glycogenesis.
Activation
Glucose-1-phosphate -> UDP-glucose
What enzyme is involved in activation (step 2) of glycogenesis?
UDP-glucose pyrophosphorylase
What enzyme separates the 2 phosphate groups formed in step 2 of glycogenesis?
Inorganic pyrophosphorylase
Name step 3 of glycogenesis.
Polymerisation
UDP-glucose -> glycogen
What enzyme is involved in polymerisation (step 3) of glycogenesis?
Glycogen synthase
Name step 4 of glycogenesis.
Branching
What is the primer required for glycogen synthase?
Glycogenin
When does glycogenesis usually occur?
Post-prandially
Between meals
Name the 2 steps of glycogenolysis.
Erosion of chain ends
Debranching
What enzyme is required for step 1 of glycogenolysis (erosion of chain ends)?
Glycogen phosphorylase
Which step is the rate-limiting step of glycogenolysis?
Step 1: erosion of chain ends
How is the activity of glycogen phosphorylase regulated?
Controlled by phosphorylation
Where does glycogen phosphorylase stop acting?
4th glucose-1-phosphate
What enzymes are involved in step 2 of glycogenolysis? (2)
Alpha-(1->4)-transglycosylase
Alpha-(1->6)-glucosidase
What is the role of alpha-(1->4)-transglycosylase?
Transfer of 3/4 glucose units to end of the chain
What is the role of alpha-(1->6)-glucosidase?
Breaking off the last remaining glucose unit from the side chain
What is step 3 of glycogenolysis?
Recovery
Glucose-1-phosphate -> glucose-6-phosphate
What enzyme is involved in step 3 of glycogenolysis?
Phosphoglucomutase
What is step 4 of glycogenolysis?
Release for glycolysis or to the liver
What enzyme converts glucose-6-phosphate to glucose?
Glucose-6-phosphatase
Give 4 symptoms of glycogen storage diseases (GSD).
Muscle cramp
Muscle weakness
General tiredness
Hypoglycaemia
Hepatomegally (liver enlargement)
What occurs in liver glycogen synthase deficiency?
Glycogen can’t be polymerised
Glucose-1-phosphate remains in liver
Give 2 symptoms of liver glycogen synthase deficiency.
Hyperglycaemia
Hypoglycaemia
What occurs in Von Gurke’s Disease (glucose-6-phosphate deficiency)?
Final phosphate can’t be converted into glucose
Glucose can’t be deposited back into blood
Give 2 symptoms of Von Gurke’s disease.
Hypoglycaemia
Hepatomegally
What occurs in Cori’s Disease (amylo-1,6-glucosidase deficiency)?
Second active site of debrancher
Glycolysis blocked at branches
Give 2 symptoms of Cori’s Disease.
Hepatomegally
Hypoglycaemia
What occurs in Andersen’s Disease (amylo-(1,4->1,6)-glucosidase defiency)?
Brancher enzyme
Glucose release insufficiently fast
Give 2 symptoms of Andersen’s Disease.
Hepatomegally
Hypoglycaemia
Poor prognosis
What occurs in McArdle’s Disease (muscle phosphorylase deficiency)?
Muscle isoenzyme releases terminal sugars
Muscle requirements not met during exercise
Give a symptom of McArdle’s Disease.
Muscle cramps/weakness
How can glycogen storage diseases be identified?
Muscle biopsy
