Glycogen Metabolism Flashcards
What is the name of the sugar-nucleotide used in glycogen synthesis?
UDP - Glucose
What does the formation of UDP-Glucose allow?
Where is the UDP group added?
- It activates the sugar for transfer
- Added to reducing end of sugar
In a growing glycogen chain, where are new monosaccharides added?
To the non-reducing end
A growing chain of glycogen is elongated:
A) 1 sugar at a time
B) 2 sugars at a time
C) By joining linear polysaccharide chains together
A
Describe how branching enzyme creates branches in the growing glycogen chain.
The enzyme removes a section of the chain and relocates it to an internal sugar and forms an alpha 1–>6 linkage
Why is branching advantageous for the structure of glycogen?
When glycogen is degraded, it is done at the non-reducing end. If the molecule is linear, the only 1 glucose molecule will be released at a time. If the molecule is branched, multiple non-reducing ends are available to be released resulting in greater glucose availability.
_____ is the primer used for glycogen synthesis.
A) Glucogenin
B) Glucouridine
C) Glycogenin
D) Glycosamine
C
Describe the process of glycogenin initiation of glycogen synthesis.
Glycogenin is a protein. It has a specific tyrosine residue that self glucates (reacts with 8 monomers of UDP-glucose) non-enzymatically to form a preliminary glucose chain. Once glucated, glycogen synthase and branching enzyme act on the primed glycogenin to create glycogen.
Describe the structure of mature glycogen
- Glycogenin core
- 12 tiers of glycogen polymers
- Each tier has 12-14 glucose and 2 branches
Glycogen phosphorylase is responsible for breaking down glycogen. Describe this process.
Enzyme adds inorganic phosphate across the glycosidic bond to generate glucose - 1 - phosphate. This occurs at the terminal glucose monomer in glycogen chains/branches.
How can glucose metabolism regulate glycogen phosphorylase?
If glycogen breakdown outpaces glucose utilization, the glucose monomers can feedback and inhibit glycogen phosphorylase to inhibit further production of glucose and breakdown of glycogen.
What is the isoform of glycogen phosphorylase in the muscle cells called?
Myophosphorylase
