Glycogen metabolism Flashcards
What are the properties of glycogen?
Helical structure
12-14 glucose chain
branch occurs every 8-12 glucoses
Describe the glycogen structure
3D branches
120,000 glucose per glycogen molecule
10-40nm diameter
What is the purpose of glycogenolysis?
To convert glycogen to glucose in a two step conversion
What is the first step of glycogenolysis?
Using a Pi group, Glycogen phosphorylase breaks the alpha 1,4 bonds
or
A debranching enzyme will break off side chains at 1,6
What is the product after step 1 of glycogenolysis?
Glucose 1-phosphate and a glycogen (n-1) residue
What is the second step of glycogenolysis?
The phosphate on carbon 1 gets removed by phosphoglucomutase
The original phosphate on the enzyme gets inserted onto the 6 carbon
What is the product of the second step of glycogenolysis?
Glucose 6 phosphate
What enzymes are used in glycogenolysis?
1,6 glucosidase (a transferase)
Glycogen phosphorylase
Phosphoglucomutase
What are the traits of phosphorylase?
It works one chain at a time
Multiple chains can be worked on by multiple enzymes
Can’t break 1-6 bonds or 1,4 bonds within 4 units of a branch point
What happens to glycogen branches?
The chains are trimmed within 4 units of the branches
Transferase then detaches the excess three and attaches them to the main chain
Glucosidase then hydrolyses the single unit into a free glucose
Why is glycogenolysis and phophorolysis used?
Because breaking down glycogen into glucose and then glucose-6-phosphate requires ATP
What is glycogenesis?
The conversion of glucose to glycogen
Is glycogenolysis reversible?
Yes but this doesn’t occur because the Pi concentration is much bigger than G-1-P so the reaction only happens one way
What is the first step of glycogenesis?
Glucose-6-phosphate gets converted to Glucose-1-phosphate by phosphoglucomutase
What is the second step of glycogenesis?
Uridine triphosphate UTP is added to the g-1-p, catalysed by UDP-Glucose pyrophosphorylase.
The product is uridine diphosphate and two phosphate molecules
