Chapter 24 & 25- Glycogen Flashcards
What is glycogen?
Where are the largest stores of glycogen?
Highly branched homopolymer of glucose present in all tissues
Largest stores of glycogen are in liver and muscle
Liver breaks down glycogen and released glucose to the blood to provide energy for the brain and red blood cells
Muscle glycogen stores are mobilized to provide energy for muscle contraction
(Muscle is for its own good while glucose stored in liver for the body’s sake)
What is the structure of glycogen?
Slide 3
2000 non reducing ends can break down glucose
All alpha 1-4 linkages, only one has an alpha 1-6 linkage at the start
What is glycogenolysis?
What is glycogenesis?
Glycogenolysis- degradation of glycogen
Glycogenesis- biosynthesis of glycogen
Glucose 6 phosphate enters glycolytic pathways Nd works on producing energy
Slide 4
How is glucose 1 phosphate converted into UDP-glucose?
What enzyme does this?
What is pyrophosphorylase, phosphorylase, and hydrogenase?
Slide 5
Done by UDP-glucose Pyrophosphorylase
Pyrophosphates are very unstable so they are converted to stable Pi
(When Pi is involved it’s called phosphorylase, when ppi is involved it’s pyrophosphorylase, and with water it’s hydrogenase)
What is glycogen synthase?
What does it do?
Key regulatory enzyme in glycogen synthesis, transfers a glucose moiety from UDP-glucose to the C-4 terminal residue of a glycogen chain to form a α-1,4-glycosidic bond
Slide 7
What is the difference between synthetase and synthase?
Synthase does synthetases part but doesn’t use energy
What is a branching enzyme?
Slide 8
Branching enzyme forms branch and attach more glucose using alpha 1-4 linkages
Gives us two nonreducing ends to add glucose to
How is glycogenesis initiated? (3 steps)
- Glycogenin has self catalyzed attachment of glucose residues to Tyr 194 OH of glycogenin
- Extension of glucan chain up to 8 glucose residues by glycogenin (this is the primer for initiation of glycogen synthesis)
- Glycogen synthase further extends the chain
Slide 9
What does glycogen phosphorylase do?
Degrades glycogen from the nonreducing ends of the glycogen molecule
This results in glucose 1 phosphate and glucose with one less residues
Slide 10
What type of enzyme is needed for the breakdown of glycogen besides glycogen phosphorylase? (At branch points)
A debranching enzyme is needed since glycogen phosphorylase cannot cleave bear branch points (only cleaves α-1,4-glycosidic bonds)
Transferase shifts a small oligosaccharide near the branch point to a nearby chain, thereby making the glucose moieties accessible to the phosphorylase, a debranching enzyme (α-1,6-glucosidase) then cleaves the α-1,6 bind at the branch point which releases free glucose
Slide 12
How is glucose 1 phosphate converted to glucose 6 phosphate?
By what enzyme?
Phosphoglucomutase converts it
Liver contains glucose 6 phosphatase which generates free glucose from glucose 6 phosphate (glucose is to be used by brain and red blood cells
Glucose 6 phosphate is absent in most other tissues
Slide 13
How is glycogen phosphorylase (GP) interconverted between active (a) and inactive (b)?
Slide 14!!
GPA- glycogen phosphorylase is active (has phosphate group attached to it)
GPB- glycogen phosphorylase is inactive (no phosphate means inactive)
What are the activators and inhibitors of glycogen phosphorylase I’m muscle and in liver?
Muscle:
Inhibitors- ATP and G6P
Activators- AMP
Liver:
Inhibitor- glucose
Activators work in an inactive enzyme and make it active
Inhibitors work in an active enzyme and make it inactive
High energy means you don’t want glycogen breakdown
Low energy means high concentration of AMP which activates
What are the 2 ways to control glycogen phosphorylase (breakdown of glycogen)?
Phosphorylation and dephosphorylation
Activators and inhibitors
How is glycogen synthase interconverted between GS “a” (active) and GS “b” (inactive)?
What is an activator in both muscle and liver?
Slide 17!!
Non phosphorylated in active form
Phosphorylated is the active form
In both muscle and liver, glucose 6 phosphate is an activator!
