Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
29 Cards in this Set
- Front
- Back
describe glycogen
|
a polymerized form of glucose, found at higherst concentration in liver and muscle tissues
|
|
What is the purpose of glycogen in muscles
|
serves as a rapdily mobilizable soruce of glucose-6- phosphate to power muscle contraction
|
|
What is the purpose of glycogen in the liver
|
glycogen is mobilized to maintain blood glucose levels during fasting
|
|
How is glucose exported to the blood from the liver
|
glucose 6 phosphate from glycogen must be hyrdolyzed to glucose using glucose 6 phosphatase
|
|
What enzyme is responsible for they hydrolysis of glucose 6 phosphate to glucose in the liver
|
glucose 6 phosphatase
|
|
Why is the glucose 6 phosphate released from glycogen in muscle cells not used to maintain blood glucose levels
|
muscles cells lack glucose 6 phosphatase so the G6P cannot be converted to glucose
|
|
Describe the bonding in glycogen
|
it is a branched polymer of D glucose. The linear portions are linked by alpha 1-4 bonds and the branch points are formed by alpha 1-6 bonds
|
|
What is the key intermediate in both glycogen synthesis and degradation
|
glucose 1 phosphate
|
|
what is the first step in glycogen synthesis
|
the reversible conversion of glucose 6 phosphate to glucose 1 phoshate. This invovles the breaking of a phosphoester bond and the formation of hemiacetal phosphate
|
|
What is the second step (the first irreversible step) in glycogen synthesis
|
Glucose 1 phosphate reactions with UTP to form UDP glucose and pyrophosphate
|
|
Why is the conversion of glucose 1 phosphate to UDP glucose irreversible
|
While the conversion of glucose 1 phosphate to UDP glucose and pyrophosphate is essentially reversible (one pyrophosphate bond is broken and another is formed) the pyrophosphate product is rapidly hyrolyzied to two inorganic phosphates which drives the reaction fowards
|
|
What enzyme is responsible for the extension of glycogen molecules and how does it work
|
glycogen synthase, it catalyses the transfer of glucosyl units from UDP glucose
|
|
How are glycogen branches made
|
a branching enzyme transfers 6-7 glucose residues from the end of a chain to the C6 of a glucose reside on another region of the glycogen molecule
|
|
What is the advantage of branching in glycogen
|
it increases the number of ends available for the addition and removal of glucose units and makes the process more efficient
|
|
how is glycogen degraded
|
Glycogen phosphorylase catalyses the phosphorylytic cleavage of alpha 1-4 linkages with release of glucose 1 phosphate
|
|
Which is glycogen degradation essentailly irreversible
|
the concentraiton of inorganic phosphate (a substrate) is much higher than glucose-1- phosphate (a product) this drives the reaction fowards
|
|
Which point in glycogen degradation is regulated
|
glycogen phosphorylase
|
|
How is glucose 1 phosphate converted back to glucose 6 phosphate
|
The reverse steps used in synthesis (don't need to know the details)
|
|
glycogen has ___ reducing end(s) and ___ non reducing end(s)
|
glycogen has 1 reducing end and many non reducing ends
|
|
What two hormones play key roles in the mobilization of glycogen reserves
|
adrenaline (has a greater effect on musles) and glucagon (acts on the liver only)
|
|
What process do adrenaline and glucagon initiatie
|
glycogenolysis
|
|
How are the glycogenolytic effects of adrenaline and glucagon medaited
|
cAMP dependent protein kinase A
|
|
What do adrenaline and glucagon bind to increase cAMP levels
|
they bind g protein coupled receptors which activated adenylyl cyclase
|
|
What two events relevant to glycogen metabolism occur downstream of activated PKA in in response to glucagon or adrenaline binding
|
glycogen synthase is inactivated through ATP dependent phsophorylation, phosphorylase kinase is activated by ATP dependent phosphorylation, it then goes on to phosphorylate (ATP dependent) glycogen phosphorylase and activate it
|
|
Phosphorylation of glycogen synthase by PKA activates/ inactivates it
|
inactivates
|
|
PKA dependent Phosphorylation of phosphorylase kinase activates/ inactivates it so it can activate/ inactivate glycogen phosphorylase
|
phosphorylation of phsophorylase kinase activates the enzyme so it can activate (via phosphorylation) glycogen phosphorylase
|
|
Kinases add phosphate groups to enzymes to regulate them. What enzymes do the reverse
|
protein phosphatases
|
|
where is glycogen stored, why is it important to store glucose in this manner
|
it is stored in the liver cytoplasm ,storing glucose as a large polyer allow the cell to maintain osmotic balance
|
|
Approximately how many glucose molecules are stored in one glycogen
|
~50,000
|