HANDOUT: GLYCOGENESIS and GLYCOGENOLYSIS Flashcards
This is the storage form of glucose
Glycogen
How many anomeric carbons does glycogen have?
1 only, although highly branched
This is not linked to another glucose residue
What links the glucosyl of glycogens?
a-1,4-glycosidic bonds with a-1,6-branches every 8-10n residues
The anomeric carbon is attached to a certain protein at the beginning of the chain. What is this protein? What is the unattached end called?
Glycogenin
Non-reducing end –> unattached end
What is the function of the branching structure of the glycogen?
rapid degradation
rapid synthesis of glycogen
[since enzymes can work on different branches at a time]
The molecular weight of glycogen polymers present in tissues
107 to 108 Da
Where are the regulatory enzymes involved in glycogen synthesis and degradation bound to glycogen particles?
Surface
The function of glycogen in most cell types
- reservoir for glucosyl units
Muscle glycogen vs Liver glycogen
Muscle glycogen - fuel for ATP production
Liver glycogen - glucose reserve for maintenance of concentration of glucose
When is Glycogen an essential fuel source for skeletal muscles?
- High ATP demand
- G6P is being rapidly used in anaerobic glycolysis (During exercise, for example, the glucose is now used rapidly (thus are the G^Ps) in glycolysis, hence why glycogen takes place)
Small glycogen reservoir function in other cells
- Emergency fuel source that can be used for ATP generation (when O2 is absent or when blood flow is restricted)
The first and immedia†e source of glucose for maintaining blood glucose level
Liver glycogen
In the liver, describe what happens to G6P glycogenolysis.
G6P is derived from a degraded glycogen, then glucose-6-phosphatase will hydrolyze gG6P into glucose, which will go into the bloodstream.
The enzyme that is only present in the liver and kidney
G-6-phosphatase
What does glycogen degradation provide?
- source of blood glucose when dietary glucose decrease
- when there’s an increase in exercise
when muscles use lots of glucose
Describe how glycogen is synthesized
- Glucose enters liver via GLUT2
- Glucose –> G6P (Glucokinase)
- G6P –> G1P
- G1P + UTP —> UDP [active] (pyrophosphatase)
- Glycogenin —> —> Glycogen
Describe how glycogen is degraded
- glycosidic bonds between glucosyl of glycogen are broken
- phosphate groups are added
- G1P is formed
- UDP is not synthesized
This glycosidic bond is required in Glycogen synthesis to link glycosyl residues in long chains
α-1,4-glycosidic bonds
This glycosidic bond is required in Glycogen synthesis to link glycosyl in every 8-10 residues
α-1,6-branch
Describe the lengthening of the polysaccharide chains of a pre-existing glycogen molecule
- Most glycogen synthesis occurs through the lengthening of the polysaccharide chains of a preexisting glycogen molecule (polymer)
- reducing end attaches to glycogenin
How to lengthen glycogen chains?
- glucosyl residues are added from UDP to the non-reducing end
- this is facilitated by glycogen synthase
What facilitates the addition of UDP to the non-reducing end
glycogen synthase
The anomeric carbon of each glucosyl residue is attached in an _______________.
α-1,4-glycosidic bond
to the hydroxyl on C4 of the terminal glucosyl residue.
When the chain reaches ______, the residues are cleaved.
approximately 11 residues
