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Glycogen

Terms in this set (41)

Glucose is stored in the form of what?
glycogen
where can glycogen be found?
in the liver and muscle cells
what is a good indicator that in a cell that glucose will be stored in the form of glycogen in liver and/or muscle cell?
if that particular cell has a high concentration of glucose-6-phosphate.
True or False. Glucose-6-phosphate has a total of 6 different paths that it can react to after it is formed from glucose?
true
In the general sense how does glycogen breakdown (glycogenolysis) occur?
One unit of glucose gets removed at a time beginning from the non-reducing end.
what are the 3 enzymes needed for the breakdown of glycogen? think about the process.
phosphorylase, de-branching enzyme, and phosphoglucomutase.
In glycogen breakdown what is the role of phosphorylase enzyme?
to split the glucose molecule from the branch. This continues until the branch reaches a residue 4 from the branch point.
Phosphorylation is the first type of reaction that occurs in the breakdown of glycogen. Where does the phosphorylation occur? and when does it stop?
starting w/ the glucose at the non-reducing end. Between the alpha 1-4 linkage. Stops at the 4th residue from the branching site of glycogen.
At the branching point in glycogen what two linkages exist?
alpha 1-4 and alpha 1-6.
After the first enzyme (Phosphorylase) catalyses phosphorylation the glycogen strand is left w/ 2 sub-branches w/ 4 glucose molecules each. What is the next step?
de-branching at the alpha 1-4 link from the alpha 1-6 linkage.
What does the de-branching leave behind in the glycogen form?
it leaves one glucose molecule w/ an alpha 1-6 linkage and the 4 glucose molecules linked to the branch by the alpha 1-4 linkage.
What else happens at this branching point. Where only the one alpha 1-6 glucose and the alpha 1-4 branch are linked?
the same de-branching enzyme (Transglycosylase) hydrolyzes the alpha 1-6 linked glucose to produce glucose. Now only a glucose branch is left behind.
The last enzyme involved w/ the breakdown of glycogen is called phosphoglucomutase. Since it is not DNA it does not cause a mutation but rather what? Goes from glucose-1-phosphate to what?
causes isomerization (change in bond formation). Phosphoglucomutase causes a isomerization type of reaction that turns glucose-1-phosphate into glucose-6-phosphate.
What is the end product once glycogen breakdown?
Glucose-6-phosphate.
what is the difference of glucose-6-phosphate in the muscle vs liver?
muscle goes into glycolysis. Liver into gluconeogenesis.
What is the difference between glucose-6-phosphate going through glycolysis vs gluconeogenesis?
in gluconeogenesis it needs the enzyme glucose-6-phosphatase to catalyze the reaction and create glucose from glucose-6-phosphate. In muscle is a spontaneous reaction (high in energy).
glucose-6-phosphatase is a location specific enzyme found where?
in the liver.
What function does glucose-6-phosphatase have?
it dephosphorylates glucose-6-phosphate to yield glucose in the ER lumen. Glucose is then transported out of the lumen into teh cytosol where it then can be transported out of the liver cell into the blood stream helping the glucose blood concentration.
What is the relationship between Glucose-6-phosphatase and the membrane of the ER?
glucose-6-phosphatase is an integral membrane protein of the ER.
where is the active site of the enzyme glucose-6-phosphatase?
in the lumen (inside) of the ER membrane.
In what organelle does the dephosphorylation of glucose-6-phosphate occur?
in the lumen of the ER.
true or false. Glucose-6-phosphate is produced in the cytosol. Then it gets transported into the ER lumen to get dephosphorylated. Then it gets transported out as glucose into the cytosol. then gets transported to the capillary through (GLUT2) transporter.
True.
is the synthesis of glycogen thermodynamically favorable?
no.
what is needed to synthesize glycogen?
coupled to exergonic reaction. ATP.
what is good about coupling the synthesis of glycogen to ATP?
ATP has a high phosphate transfer potential. Therefore it can pull the reaction forward.
What is the starting material for glycogen?
needs to be glucose-6-phosphate because glucose is already in the liver cell and it (liver cell has recognized that glycolysis is not needed) therefore the process to synthesize glycogen from glucose begins w/ glucose-6-phosphate.
The synthesis of glycogen (glycogenesis) also requires 3 enzymes. What are they named?
1. UDP glucose pyrophosphorylase
2. Glycogen synthase
3. Branching enzyme
what is a condition of the existing glycogen chain that must be met before the UDP glucose can transfer a glucose molecule to the glycogen chain?
the existing glycogen chain that is going to accept the glucose needs to be at least four residues (glucose molecules) long in order to accept the new glucose molecule.
what does the Glycogen branching enzyme do?
transfers a 7-residue segment (must leave at least 4 residues behind) to the C-6 of same or different glycogen chain.
what two properties increase in glycogen when its residues are branched?
solubility and number of non-reducing ends.
why is increasing the number of non-reducing ends important in the synthesis of glycogen?
because when necessary glucose can be released much quicker. Can have multiple enzymes dephosphorylating (de-branching) higher number of glucose molecules at the same time.
where does glycolysis, gluconeogenesis, and glycogen breakdown and glycogen synthesis happen?
glycolysis happens everywhere. Gluconeogenesis happens in the liver cell (cytosol and mitochondrion). glycogen breakdown happens in muscle and liver cells(liver cells require additional enzyme glucose-6-phosphatase to go from glucose-6-phosphate to glucose if not it cannot leave the mitochondrion cell) and muscle. Glycogen synthesis happens in the liver and muscle cells.
Glycogenolysis and glycogenesis regulation is controlled by?
allosteric interactions and covalent modifications.
where do the enzymes found that catalyze glycogenolysis and glycogenesis?
found in the muscle and liver cells. therefor synthesis and breakdown is tightly regulated.
why does muscle break down glycogen. what purpose?
for its own use in muscle contraction.
True or false. Can hormones mediate both the breakdown and synthesis of glycogen?
yes.
What is the name of the hormone that triggers a response for glycogen breakdown in the liver?
glucagon.
How does glucagon signal?
the pancreas releases glucagon when it senses the blood glucose concentration is lower than 4-5 mM. The glucagon goes into the capillaries into the liver cells where it binds to a receptor. This signals mechanism to initiate the breakdown of glycogen.
Does glucagon signal only both the liver and muscle cells?
no. Only the liver.
since glucagon signals liver cells. What signals muscle cells?
Epinephrine or norepinephrine (aka adrenaline).
why cant glucagon signal muscle cells?
because it does not have a glucagon receptor.
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