Chapter 24: Glycogen Degradation Flashcards
Glycogen is a highly branched…
Homopolymer of glucose
Most of the glucose residues in glycogen are linked by ______ bonds; about every 10 residues there is a ______.
Linked by a-1,4 glycosidic bonds
a-1,6 glycosidic branch
Largest stores of glycogen are in…
Liver and muscle
Liver breaks down glycogen and releases glucose to the bloodstream to provide energy for…
Brain and RBCs
Muscle glycogen stores are mobilized to provide energy for…
Muscle contraction (Requires ATP)
Glycogen degradation consists of 3 steps:
- Release of glucose 1-phosphate
- Remodeling of the glycogen substrate
- Conversion of glucose 1-phosphate into glucose 6-phosphate
Glucose 6-phosphate has 3 fates:
- Glycolysis
- Pentose phosphate pathway
- Conversion to glucose - released into bloodstream
Glycogen releases Glucose 1-phosphate via
Glycogen phosphorylase (Catalyst of this phosphorolysis reaction)
Glycogen phosphorylase hydrolyzes _____.
a-1,4 glycosidic bonds
Phosphorolysis of glycogen is _____ by releasing a phosphorylated sugar.
Energetically favorable (Whereas if you use a free glucose, ATP is required)
What else is needed for the breakdown of glycogen?
A Debranching Enzyme:
a-1,6 Glucosidase
&
Transferase
How does transferase remodel glycogen?
Shifts a block of 3 glycosyl residues from one outer branch to the other
How does a-1,6 Glucosidase remodel glycogen?
a-1,6 Glucosidase cleaves the a-1,6 glycosidic bond at the branch point, releasing free glucose
In summary, Glycogen phosphorylase cleaves _____ which releases _____.
Cleaves a-1,4 glycosidic bonds
Releases glucose 1-phosphate
In summary, Debranching enzyme cleaves _____ which releases _____.
Cleaves a-1,6 glycosidic bonds
Releases glucose
Glucose in Glycogen is released as:
90% Glucose 1-phosphate (a-1,4)
10% glucose (a-1,6)
What converts Glucose 1-Phosphate into Glucose 6-Phosphate?
Phosphoglucomutase
What is the intermediate from Glucose 1-Phosphate to Glucose 6-Phosphate?
Glucose 1,6-bisphosphate
The conversion of Glucose 1-Phosphate to Glucose 6-Phosphate is an important conversion because…
It is needed so that glycogen can enter the metabolic mainstream
*Phosphoryl shift reaction that does not require ATP
What hydrolytic enzyme is absent from muscle, but present in the liver?
Glucose 6-Phosphatase
Glucose 6-Phosphatase generates _____ from _____ in the liver.
Free glucose from Glucose 6-Phosphate
The free glucose is released into the blood for use by other tissues such as the brain and RBCs.
Glycogen phosphorylase has _____ which is a derivative of _____ as prosthetic group.
Has pyridoxal 5’ phosphate (PLP)
Derivative of pyridoxine (vitamin B6)
The 5’ phosphate of PLP serves as _____ and as _____ (acid-base catalysis).
Proton donor and as proton acceptor
A deficiency in _____ can affect glycogen degradation.
Vitamin B6
PLP participates in…
The phosphorolytic cleavage of glycogen
Phosphorylase is regulated by…
Allosteric interactions and Reversible phosphorylation