Glucose Flashcards
How is glycogen stored in muscle and liver cells of vertebrates
cystosolic granulaes
what is glycogenolysis
the degradation of glycogen
what does glycogen breakdown yield?
G1P which can be converted to G6P for metabolism via glycolysis and the citric acid cycle
What is most of the G6P in the liver converted to?
it is converted to glucose and delivered to other cells such as the brain, enthrocytes and adipocytes
What does glycogen phosphorlase catalyze?
phosphorylysis which cleaves the bond by transferring an oxygen atom of phosphate
Where does the enzyme remove the residues from?
the non-reducing ends of the glycogen
What specific glucose molecules does glycogen phosphorylase act on? Where does it stop?
it acts on 1-4 linkages
4 residues from the branching point
What is GP?
It is a dimer of 2 identical lobed subunits
Where are catalytic sites?
they are in the clefts between the two domains of each subunit.
What is the difference between phosphorylase a and phosphorylase b?
a- is the more active form
b- the less active form. It is dephosphorylated
After glycogen phosphorylase is finished what is the product and what happens to it?
the result is limit dextrin, which is further degraded by the glycogen-debranching enzyme.
How many glucose residues does glucanotransferase relocate? The debranching enzyme catalyzes the removal of what linked glucose?
3
the alpha 1-6 linked
How many ATPs are yielded by each glucose molecule
3 ATP
How is G1P conversted to G6P?
phosphoglucomutase
What is the significance of G6P?
it is an intermediate of several cellular pathways
How much dietary glucose is converted to glycogen?
2/3
How is cellular glucose converted to G6P?
Hexokinase
What is a major regulatory step in glycogen synthesis?
Glycogen synthase
What is the enzyme intermediate in the first step between G6P and G1P?`
phosphoglucomutase
the second step in glycogen synthesis is G6P to UDP glucose. What is the enzyme intermediate?
UDP-glucose pyrophosphorlase
What is the last enzyme used in the glycogen synthesis process when going from UDP-glucose to Glycogen?
glycogen synthase
Which side of glycogen does glycogen synthase add glucose onto?
the non-reducing end
What are the three hormones that regulate glycogen metabolism?
Insulin, glucagon and adrenaline
What is muscle glycogen used for?
it is fuel for muscle contraction
What is liver glycogen used for?
converted to glucose for the bloodstream transport to other tissues
Where is insulin produced and when is it secreted?
it is created in the beta cells of the pancreas, and is secreted when the glucose levels of the blood are high because of the fed state)
What does insulin do?
it increases the availability of the GLUT4 transporters on the cell surface for the cell to take up more glucose into muscle and adipose tissue.
How does insulin stimulate glycogen synthesis in the liver?
-causes a depolarization of a specific site on glycogen synthase and affects the signaling pathway and the protein kinase cascade.
Where is glucagon created and when is it secreted?
It is created in the beta cells of the pancreas. and is secrete when the blood indicates low levels of glucose present.
What does glucagon stimulate?
It stimulates glycogen degradation to restore blood glucose to steady-state levels.
What cells are the only ones rich in glucagon receptors
liver cells
Where is adrenaline released from
released from the adrenal glands in response to the flight or fight mechanism
What does adrenaline stimulate?
the breakdown of glycogen to G1P- which is later converted to G6P. the increases amount of g6P increases both the rate of glycolysis in the muscle and the glucose release into the blood stream.
What two enzymes control glycogen metabolism in liver and muscle cells?
glycogen phosphorylase and glycogen synthase
True or false: when glycogen phosphorylase is active, glycogen synthase is also active.
false, when GP is active, GS will be inactive. They are reciprocally regulated.
How does covalent regulation occur?
by phosphorylation (added a phosphate) and dephosphorylation (adding a OH group)
Is the phosphorylated form of (active form) of GP inhibited by G6P?
yes
Is the active form (dephosphorylated form) of GS inhibited G6P?
no, it is activated
