Glycogen Flashcards
How can we obtain glucose for the body?
The diet
Degradation of glycogen
Gluconeogenesis
Which source of glucose is faster: glycogen synthesis or gluconeogenesis?
Glycogen Synthesis
Where is most glycogen found and stored?
In the liver or muscle
From what source is the glycogen provided for blood glucose?
Liver
How much glycogen is found in muscle?
400 g
How much glycogen is found in the liver?
100 g
List three properties of Glycogen
Branched polysacharide
Alpha (1-4) glycosidic bonds
Branches of Alpha (1-6) glycosidic bonds
Where and how in the cell is glycogen stored?
As small granules in the cytoplasm of cells.
What will happen to glycogen stores in the liver while eating?
Increase
Glycogen is synthesized from what molecule and what does it require?
Alpha-D-Glucose and requires ATP and Uridine Triphosphate (UTP)
One of the first steps is the conversion of Glucose-6-Phosphate to ___________ by the enzyme ___________.
Glucose-1-Phosphate by the enzyme Phosphoglucomutase
What enzymes catalyzes the conversion of Glucose-1-Phosphate to UDP-glucose?
UDP-glucose pyrophosphoryase
What compound is the source of ALL the glucose residues in the synthesis of glycogen?
UDP-glucose
What enzyme makes the chains of alpha(1-4) glycosidic linkages in glycogen? What can it not use?
Glycogen synthase - cannot use free glucose to act as an acceptor molecule for UDP-glucose.
What protein will add glucose onto itself? What is this process called?
Glycogenin - autoglucosylation
What will glucose use to attach to the glycosylated glycogen?
UDP-glucose
When can glycogen synthase start to build the glycogen chain?
Once a few monomers of glucose are linked forming a primer.
How is elongation of the glycogen chain happening?
Glucose-UDP is transferred to the non-reducing end of the growing chain.
Where will the new glycosidic bond be formed? What is the linkage made by?
The anomeric hydroxy group of the UDP-glucose and carbon 4 of the accepting glucose molecule. Made by glycogen synthase.
The released UDP can be phosphorylated by what energy rich compound?
ATP
What enzyme is responsible for this to occur?
Nucleoside Diphosphate Kinase
What is amylose?
Unbranched glucose linked by Alpha (1-4) linkages found in plants.
The branching of glycogen occurs at every __ residues of glucose?
8
Branching increases the number of non-reducing ends to which new glucose can be added. This greatly speeds up what?
The synthesis of glucose.
What is the name of the branching enzyme?
Amylo-alpha-(1-4) - alpha-(1-6) transglucosidase
How does this branching enzyme work?
Cleaves off 6-8 glucosyl residues breaking a alpha(1-4) bond in the process.
What happens to these glucose residues after being broken off?
They are then attached to a non-terminal glucose residue by a alpha-(1-6) linkage.
Is the breakdown of glycogen the reversal of the making of glycogen?
No
When glycogen is broken down the end products are…
Glucose-1-phosphate and some free glucose
Glucose-1-phosphate is obtained from the breaking down of what type of bonds?
Alpha(1-4) glycosidic linkages.
How is the free glucose obtained?
The breaking down of each alpha(1-6) glycosidic bond.
What enzyme will cleave the alpha(1-4) bonds from the non-reducing end?
Glycogen Phosphorylase
How many glucose units will remain on each chain after the chain is cleaved by glycogen phosphorylase?
4
What does Glycogen phosphorylase require to function?
The co-enzyme pyridoxal phosphate which is Vit B6
What is the name of the structure that remains after the glycogen is cleaved?
Limit Dextrin and it cannot be degraded further by glycogen phosphorylase.
How many enzymatic reactions are required to remove the branches?
2
The first enzymatic reaction to remove the branches uses what enzyme? How any of the four glucose residues will it remove?
oligo-alpha(1-4) - alpha (1-4) glucan transferase. Will remove 3 of the 4 residues
Where do the 3 residues get transferred to on another glycogen molecule?
To the nonreducing end of another chain lengthening that chain.
The single glucose that was not cleaved off by the transferase will be removed by what enzyme? What will it release?
amylo-alpha (1-6) glucosidase. Will release free glucose.
Where in the cell is glucose-1-phosphate converted to glucose-6-phosphate?
Phosphoglucose mutase.
The conversion of glucose-1-phosphate to glucose-6 takes place through what intermediate?
glucose 1,6 bisphosphate
In the liver, glucose-6 phosphate is transported where by glucose-6-phosphate translocase?
The endoplasmic reticulum
In the endoplasmic reticulum glucose-6-phosphate is converted to glucose by what enzyme?
Glucose-6-phosphatase
In muscle tissue, where does glucose-6-phosphate enter and why?
Glycolysis as muscles lack glucose-6-phosphatase
What percent of glycogen is broker down in the lysosomes?
1-3%
What is the enzyme called that breaks glycogen down in the lysosomes?
acid alpha(1-4) glucosidase
A deficiency in this enzyme will cause what effect?
An accumulation of glycogen in cavuoles in the lysosomes resulting in muscle weakness.
About 1 in how many individuals will be born with a glycogen storage disease.
40 000
GSD 1 is what condition and what enzyme is flawed?
Von Gierkes Disease - glucose-6-phosphatase (cannot convert glucose-6-phosphate to glucose)
Pompe’s Disease is GSD __ and impacts what specific enzyme?
II - acid alpha-glucosidase (causes an accumulation of glycogen in vacuoles within lysosomes = muscle weakness)
GSD IV aka? enzyme?
Andersen Disease - amylo 1-4, 1-6 transglucosidase
Pompe’s disease can also be called?
Acid Maltase Deficiency
The accumulation of glycogen in the tissue with Pompe’s Disease will give what appearance?
Appearance of pseudo-hypertrophic muscles.
Pompe’s disease will affect what structures and cause what symptoms in the body?
The diaphragm, the heart and tongue are enlarged, lordosis, kyphosis and death is usually by heart failure
Andersen’s is described as a bad Cori’s disease and is due to a deficiency in what enzyme?
Glycogen branching enzyme amylo1-4, 1-6 transglucosidase.
This deficiency will affect glycogen how? What will the clinical symptoms be?
Accumulation of abnormal glycogen with long outer branches. Clinical features are muscle hypotonia and Cirrhosis - death from liver disease.
