Glycogen Metabolism

Question 1

Osmotically inactive and readily mobilized form of glucose

Answer 1

Glycogen

Question 2

Glycogen is a branched long chain _______ of glucose molecules

Answer 2

Homopolymer

Question 3

Glycogen is ____ layers of glucsoe with approx. ________ glucose residues

Answer 3

12, 55,000

Question 4

In glycogen glucose is linked together via _____

Answer 4

alpha 1-4 glycosidic bonds

Question 5

Glycogen has branch points every ____ residues formed via ________ between glucose monomers of separate chains

Answer 5

12, via alpha 1,6 glycosidic bonds

Question 6

The non-reducing ends of glycogen each contain a terminal glucose with a free hydroxyl group at

Answer 6

C4

Question 7

The Reducing end of glycogen has a glucose monomer connected to a protein called a

Answer 7

Glycogenin (note that glycogenin is a complex with Mn, UDP and maltohexaose)

Question 8

Glycogenin helps to make a _____ which is crucial for glycogen synthesis

Answer 8

primer

Question 9

Glycogen is stored in the

Answer 9

liver, muscle, and other tissues

Question 10

Glycogen can be present as ______ which not only contain glycogen but also the enzymes needed for its metabolism

Answer 10

Granules

Question 11

What is the function of liver glycogen

Answer 11

regulates overall blood glucose levels

Question 12

What is the function of muscle glycogen

Answer 12

provides reservoir of fuel (glucose) for physical activity for muscles

Question 13

pathways for glycogen synthesis and degradation are regulated

Answer 13

independently

Question 14

What are some modes of regulation of glycogen synthesis and degradation

Answer 14

allosteric control
covalent modification through reversible phosphorylation of key enzymes
Hormonal control

Question 15

what are the three pathways that glucose 6-P can take

Answer 15

it can enter glycolysis
free glucose for release into blood stream
pentose phosphate pathway- NADPH and ribose derivative

Question 16

What are the names of the key enzymes in glycogenolysis

Answer 16

Glycogen phosphorylase (GP)( rate limiting enzyme)- catalyzes the cleavage of glycogen, chain shortening occurs at the nonreducing end of the polmer

Transferase- transfers block of 3 of the remaining 4 glucose to the non-reducing end of the main chain forming an alpha- 1,4 bond

Debranching enzyme or alpha 1,6-glucosidase- cleaves the alpha 1,6 bond of the single remaining glucose residue to release the free glucose

Phosphoglucomutase- converts glucose 1-P to glucose 6-P

Glucose 6-Phosphatase- Cleaves off phosphate and makes glucose

Question 17

What is the rate limiting step of glycogenolysis

Answer 17

Glycogen phosphorylase (GP)

Question 18

Where does glycogen phosphorylase (GP) shorten the chain

Answer 18

at the non-reducing end of glycogen polymer

Question 19

glycogen phosphorylase does not require ATP but instead adds a ______ and releases glucose residue as glucose-1-P

Answer 19

Orthophosphate

Question 20

Glycogen phosphorylase (GP) uses what as a cofactor

Answer 20

Pyridoxal phosphate (vitamin B6)

Question 21

Phosphorolysis of glucose residues continues till the Glycogen phosphorylase (GP) gets within ____ residues of the alpha-1,6 linkage of a branch point

Answer 21

4

Question 22

What enzyme transfers a block of 3 of the remaining 4 glucoses to the non-reducing end of the main chain forming an alpha-1,4 bond

Answer 22

Transferase

Question 23

What enzyme cleaves the alpha 1,6 bond of the single remaining residue to release the free glucose

Answer 23

Debranching enzyme/ alpha-1,6- glucosidase

Question 24

The free glucose cleaved of the glycogen by debranching enzyme/alpha 1,6 glucosidase is phosphorylated by

Answer 24

hexokinase

Question 25

What is the function of phosphoglucomutase

Answer 25

it converts Glucose 1-P to glucose 6-P (Note that the phosphoryl group is transferred form the enzyme to the substrate, and a different phosphoryl group is transferred back to restore the enzyme to its initial state

Question 26

Glucose 6-Phosphatase is only located in

Answer 26

The liver

Question 27

What is the function of glucose 6-phosphatase

Answer 27

it converts Glucose 6-Phosphate into glucose

Question 28

Glycogen phosphorylase is regulated by

Answer 28

``` several allosteric effectors (signal energy state of the cell) reversible phosphorylation (responsive to hormones) ```

Question 29

Glycogen phosphorylase exists in an active a form located in the _____ and an incactive b form located in the _____

Answer 29

liver, muslce

Question 30

Glycogen phosphorylase b form is activated to a form by what enzyme

Answer 30

phospohrylation fo a single serine residue with phosphorylase kinase (with 2 ATP)

Question 31

____ is a allosteric inhibitor of phosphorylase a in the liver and moves it to the T (tense) state

Answer 31

glucose

Question 32

b phosphorylase is in the R (relaxed state) when what is high

Answer 32

AMP (binds to active site and stablilizes conformation of b in the active R state) (note that this occurs during muscle contraction because ATP is converted to AMP by myosin and adenylate kinase signaling the GP to breakdown glycogen)

Question 33

What are negative allosteric regulators of glycogen phosphorylase

Answer 33

ATP and glucose 6-P

Question 34

The conversion of glycogen phosphorylase a to b is initiated by

Answer 34

hormones

Question 35

Phosphorylase kinase becomes active with

Answer 35

Ca2+ leads to partly active then phosphorylase kinase A and hormones make it fully active

Question 36

Phosphorylase kinase has 4 subunits what are they

Answer 36

(alpha, beta, gamma, delta)x4

Question 37

Phosphorylase Kinase is a large protein of about

Answer 37

1300kD

Question 38

What are the subunits of phosphorylase kinase

Answer 38

alpha- phosphorylation site beta- phosphorylation site gamma- active site delta- Calmodulin

Question 39

Epinephrine and glucagon do what to glycogen

Answer 39

induce glycogen breakdown

Question 40

glucagon and epinephrine work through

Answer 40

G protein coupled receptors (GPCR) specifically the 7TM receptor

Question 41

The liver and muscle forms of Glucose phosphorylase are products of separate genes. called

Answer 41

isozymes

Question 42

Both the liver and muscle forms of glycogen phosphorylase are activated by ____ and inhibited by ___ and ___

Answer 42

pohosphorylation by PK and inhibited by ATP and G6P (note muscle is also allosterically activated via AMP and in the liver it is inactivated via free glucose but unaffected by AMP)

Question 43

Mutation in the liver glycogen phosphorylase results in

Answer 43

Hers disease

Question 44

Mutation in the muscle glycogen phosphorylase results in

Answer 44

McArdle syndrome