Biochem Lecture 17

Front 1

describe glycogen

Back 1

a polymerized form of glucose, found at higherst concentration in liver and muscle tissues

Front 2

What is the purpose of glycogen in muscles

Back 2

serves as a rapdily mobilizable soruce of glucose-6- phosphate to power muscle contraction

Front 3

What is the purpose of glycogen in the liver

Back 3

glycogen is mobilized to maintain blood glucose levels during fasting

Front 4

How is glucose exported to the blood from the liver

Back 4

glucose 6 phosphate from glycogen must be hyrdolyzed to glucose using glucose 6 phosphatase

Front 5

What enzyme is responsible for they hydrolysis of glucose 6 phosphate to glucose in the liver

Back 5

glucose 6 phosphatase

Front 6

Why is the glucose 6 phosphate released from glycogen in muscle cells not used to maintain blood glucose levels

Back 6

muscles cells lack glucose 6 phosphatase so the G6P cannot be converted to glucose

Front 7

Describe the bonding in glycogen

Back 7

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

Front 8

What is the key intermediate in both glycogen synthesis and degradation

Back 8

glucose 1 phosphate

Front 9

what is the first step in glycogen synthesis

Back 9

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

Front 10

What is the second step (the first irreversible step) in glycogen synthesis

Back 10

Glucose 1 phosphate reactions with UTP to form UDP glucose and pyrophosphate

Front 11

Why is the conversion of glucose 1 phosphate to UDP glucose irreversible

Back 11

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

Front 12

What enzyme is responsible for the extension of glycogen molecules and how does it work

Back 12

glycogen synthase, it catalyses the transfer of glucosyl units from UDP glucose

Front 13

How are glycogen branches made

Back 13

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

Front 14

What is the advantage of branching in glycogen

Back 14

it increases the number of ends available for the addition and removal of glucose units and makes the process more efficient

Front 15

how is glycogen degraded

Back 15

Glycogen phosphorylase catalyses the phosphorylytic cleavage of alpha 1-4 linkages with release of glucose 1 phosphate

Front 16

Which is glycogen degradation essentailly irreversible

Back 16

the concentraiton of inorganic phosphate (a substrate) is much higher than glucose-1- phosphate (a product) this drives the reaction fowards

Front 17

Which point in glycogen degradation is regulated

Back 17

glycogen phosphorylase

Front 18

How is glucose 1 phosphate converted back to glucose 6 phosphate

Back 18

The reverse steps used in synthesis (don't need to know the details)

Front 19

glycogen has ___ reducing end(s) and ___ non reducing end(s)

Back 19

glycogen has 1 reducing end and many non reducing ends

Front 20

What two hormones play key roles in the mobilization of glycogen reserves

Back 20

adrenaline (has a greater effect on musles) and glucagon (acts on the liver only)

Front 21

What process do adrenaline and glucagon initiatie

Back 21

glycogenolysis

Front 22

How are the glycogenolytic effects of adrenaline and glucagon medaited

Back 22

cAMP dependent protein kinase A

Front 23

What do adrenaline and glucagon bind to increase cAMP levels

Back 23

they bind g protein coupled receptors which activated adenylyl cyclase

Front 24

What two events relevant to glycogen metabolism occur downstream of activated PKA in in response to glucagon or adrenaline binding

Back 24

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

Front 25

Phosphorylation of glycogen synthase by PKA activates/ inactivates it

Back 25

inactivates

Front 26

PKA dependent Phosphorylation of phosphorylase kinase activates/ inactivates it so it can activate/ inactivate glycogen phosphorylase

Back 26

phosphorylation of phsophorylase kinase activates the enzyme so it can activate (via phosphorylation) glycogen phosphorylase

Front 27

Kinases add phosphate groups to enzymes to regulate them. What enzymes do the reverse

Back 27

protein phosphatases

Front 28

where is glycogen stored, why is it important to store glucose in this manner

Back 28

it is stored in the liver cytoplasm ,storing glucose as a large polyer allow the cell to maintain osmotic balance

Front 29

Approximately how many glucose molecules are stored in one glycogen

Back 29

~50,000