Glycogen Metabolism and Gluconeogenesis Flashcards
What is the first thing that happens to glucose when it enters the cell?
It gets phosphorylated by hexokinase to Glucose-6-Phosphate which traps it in the cell.
Glycogen function in muscle vs liver
Glycogen in muscle is sequestered to the muscle for generation of ATP in its own cells
Liver is more generous as it uses its glycogen as a source of glucose for other tissues
What enzyme does the liver have that allows glucose 6 phosphate to exit the cell?
Glucose 6-phosphatase which cleaves the phosphate off the glucose to be able to travel via GLUT2 into the blood?
Why doesn’t the muscle share its glucose?
It doesn’t have the glucose-6-phosphatase enzyme to cleave the phosphate group which would allow it to pass through GLUT4
Glycogen is a polymer of _____ containing ______ and _________ linkages.
glucose
alpha1,4 glycosidic bonds and alpha1,6 glycosidic bonds at BRANCH points
Glycogen has lots of _______ linkages which allow for it to be stored at a high volume.
Alpha 1,6 glycosidic bonds at branch points
What are the 3 major pathways for glucose?
- Glycogen Synthesis
- Glycolysis
- Pentose Phosphate to made NADPH and nucleotide
Briefly describe the three steps of glycogen synthesis and degradation.
- G6P that has been sequestered in the cell in converted to Glucose 1- Phosphate by an isomerase.
- G1P is converted to UDP glucose which is the immediate glucose donor to glycogen
3.Glycogen can be broken down into G1P and glucose
What is UDP-glucose?
The product formed from G1P that serves as the immediate glucose donor
Glycogen is broken down into ________ and _______.
G1P and Glucose
How is G1P converted to UDP-glucose?
- The negative charged phosphate oxygen on G1P attacks the alpha phosphate of Uridine Triphosphate
- 2 phosphates from UTP are released combining G1P created UDP-Glucose.
What drives the reaction of UDP-Glucose forward?
What helps promote the incorporation of glucose into glycogen in UDP-glucose?
Hydrolysis of PPi from UDP-Glucose (Aka the two phosphate groups that were combined when G1P and UTP merged)
The high energy phosphoester bond formed between G1P and UTP favors incorporation of glucose into glycogen
________ is a primer and enzyme that catalyzes the ___________ of ______ from _______ to a _________ on the _______ on its OWN _______.
GlycoGENIN is a primer and enzyme that catalyzed the transfer of glucose from UDP-glucose to a hydroxyl group on the TYROSINE194 amino acid on it glycogenin.
Glycogenin will add ______ more _____ residues to form a ________.
What enzyme will continue this activity?
7 more glucosyl residues to form a primer
Glycogen Synthase
Synthesis of glycogen requires a _________ primer and an elongater called _______.
Glycogenin
Glycogen Synthase
What is the rate limiting step of glycogenesis?
Glycogen Synthase!
Glycogen synthase donates ______from __________ to _________ forming a _______ linkage.
Can it form the ______ bond?
glucose from UDP-glucose to glycogen to form an alpha 1,4 glycosidic linkage
It CANNOT form the alpha 1,6 branch point glycosidic linkages
Which bonds in glycogen can glycogen synthase not form?
Alpha 1,6
What can make the alpha 1,6 linkages in glycogen since ______ cannot?
Glycogen synthase cannot
BRANCHING ENZYME
Transfers group of glucosyl residues to the core and form the alpha 1,6 glycosidic bond with glucosyl residue in the glycogen core.
What is glycogenolysis and what catalyzes it?
Break down of glycogen catalyzed by Glycogen Phosphorylase
What is the rate limiting step in glycogenolysis?
Glycogen Phosphorylase
Uses inorganic phosphate to cleave the alpha 1,4 glycosidic bond and releases G1P.
Can glycogen phosphorylase break alpha 1,6 bonds?
NO
The DEBRANCHING enzyme uses water to cleave the alpha 1,6 glycosidic bond and released glucose.
Glycogen phosphorylase results in glycogen being broken down into _____ via cleavage of ________ through a _____.
Why is this important
G1P , Alpha 1,4 glycosidic bonds through an inorganic phosphate
The retention of phosphate on G1P makes it so that the glucose does not leave the cell automatically and the cell has time to decide what to do.
Glycogen Phosphorylase breaks _______ and releases _________ using ______.
Debranching enzyme breaks ________ and releases _________ using _______.
Alpha 1,4 - G1P using inorganic phosphate
Alpha 1,6 - Glucose using water
The minor product in glycogen degradation is?
Glucose
G1P is major.
Insulin favors ____________ and activates _________ in the LIVER and MUSCLE
It inhibits _________.
Glycogenesis , Glycogen Synthase
Glycogen Phosphorylase
