Exam 2 Lecture 17 Glycogen Metabolism I

Question 1

the structure of glycogen is a long chain _ of glucose with branches

Answer 1

homopolymer

Question 2

glucose molecules within linear chain linked together via _

Answer 2

alpha-1,4 glycosidic bonds

Question 3

branched points formed via _ bonds between glucose monomers of separate chains

Answer 3

alpha-1,6 glycosidic bonds

Question 4

_ contain a terminal glucose with a free hydroxyl group at carbon 4

Answer 4

non-reducing ends (multiple)

Question 5

_ consists of glucose monomer connected to a protein called glycogenin

Answer 5

reducing ends

Question 6

glycogen is _ and _ from non-reducing ends

Answer 6

degraded and extended

Question 7

glycogen is stored in:

Answer 7

liver, muscle, and other tissue

Question 8

glycogen is stored as _

Answer 8

granules

Question 9

granules contain not only glycogen but also the _ needed for glycogen metabolism

Answer 9

enzymes needed for glycogen metabolism

Question 10

defects in glycogen enzymes can lead to disorders termed _

Answer 10

glycogen storage disorders

Question 11

liver glycogen regulates

Answer 11

blood glucose levels (sensor)

Question 12

muscle glycogen provides

Answer 12

reservoir of fuel (glucose) or physical activity

Question 13

T/F: glycogen metabolism is regulated storage and release of glucose

Answer 13

true

Question 14

T/F: glycogen metabolism synthesis and degradation of glycogen involve the same pathways

Answer 14

false; synthesis and degradation are INDEPENDENT of each other

Question 15

Pathways in glycogen metabolism are regulated independently?

Answer 15

yes

Question 16

how does muscle glycogen supply energy

Answer 16

breaks down glycogen and keeps glucose in the muscle to use for activity

Question 17

what are the ways to regulate glycogen metabolism?

Answer 17

1. allosteric control
2. covalent modification
3. hormonal control

Question 18

how does allosteric control regulate glycogen metabolism

Answer 18

want to control enzyme to influence the activity of the enzyme (induces conformation change)

Question 19

how does covalent modification regulate glycogen metabolism

Answer 19

mainly through phosphorylation; reversible

Question 20

how do hormones regulate glycogen metabolism

Answer 20

insulin stimulates phosphatase, glucagon stimulates a kinase (PKA) ie hormones control covalent modifications

Question 21

What are the 3 key steps to glycogenesis

Answer 21

1. trapping and activation of glucose
2. elongation of a glycogen primer
3. branching of glycogen chains

Question 22

how does trapping of glucose occur?

Answer 22

glucokinase/hexokinase in cytosol of hepatocytes and muscle cells catalyze phosphorylation of glucose into glucose-6-ohosphate

Question 23

hows does activation of glucose occur?

Answer 23

phosphoglucomutase then reversibly isomerizes glucose-6-phosphate into glucose-1-phosphate. UDP-glucose pyrophosphorylase then transfers glucose-1P tp UTP which generates UDP-glucose (active form of glucose)

Question 24

UDP is for _

Answer 24

synthesis

Question 25

how does elongation occur?

Answer 25

elongation via glycogen synthase (rate limiting enzyme). Have a existing glycogen primer and glycogen synthase catalyzes transfer of glucose from UDP-glucose to non-reducing end of glycogen chain

Question 26

glycogen synthase forms _ glycosidic bonds between glucose molecules

Answer 26

alpha-1,4

Question 27

how does branching of glycogen chains occur?

Answer 27

when a glycogen chain reaches about 11 residues, a fragment of the chain (about 7 residues long) is broken off at an alpha-1,4 link and reattached elsewhere

Question 28

in branching, an alpha-1,4 link is broken off and attached through an _ link

Answer 28

alpha-1,6 link

Question 29

what enzyme is used for branching?

Answer 29

glucosyl (4:6) transferase

Question 30

Branching increases _

Answer 30

solubility of glycogen and increases # of terminal non-reducing ends

Question 31

glycogen degradation aka

Answer 31

glycogenolysis

Question 32

glycogen broken down to release _

Answer 32

glucose-1-phosphate (rate limiting step)

Question 33

_ remodeled to permit further degradation

Answer 33

glycogen remnant

Question 34

in glycogenolysis, glucose-1-phosphate converted to

Answer 34

glucose-6-phosphate

Question 35

glucose-6-phosphate from glycogenolysis can now enter various pathways which are:

Answer 35

1. glycolysis
2. free glucose for release into blood stream
3. pentose phosphate pathway-NADPH and ribose derivative (nucleic acid synthesis)

Question 36

how many key enzymes for glycogenolysis?

Answer 36

4

Question 37

what is the rate limiting enzyme in chain shortening

Answer 37

glycogen phosphorylase (GP) catalyzes the cleavage of glycogen

Question 38

chain shortening occurs at the _ end of the polymer

Answer 38

non-reducing end

Question 39

GP adds an _ and releases a glucose residue as glucose-1-phosphate

Answer 39

orthophosphate

Question 40

GP uses _ as a cofactor

Answer 40

pyridoxal phosphate (Vit B6)

Question 41

phosphorolysis of glucose residues continues until the GP gets within _

Answer 41

4 residues of the alpha-1,6 linkage of a branch point

Question 42

what does the phosphoglucomutase step do and how does it work?

Answer 42

mutase removes phosphate from the 1 position to the 6 position ie converts glucose-1P to glucose-6P. Adds the phosphate to position 6 first then removes phosphate from position 1

Question 43

in branch transfer, the enzyme _ transfers a block of 3 of the remaining 4 glucose to the non-reducing end of the main chain forming an alpha-1,4 bond

Answer 43

transferase

Question 44

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

Answer 44

alpha-1,6 glucosidase

Question 45

in release of glucose, glucose is phosphorylated by _

Answer 45

hexokinase

Question 46

together, transferase and alpha-1,6 glucosidase convert _ glycogen into a _ structure for further action by GP

Answer 46

convert branched glycogen into a linear structure

Question 47

in debranching, _ cuts at non-reducing end

Answer 47

phosphorylase

Question 48

in debranching of glycogen, yields _ G1P to 1G

Answer 48

10 G1P to 1G

Question 49

T/F: glucose-6P cannot get out of the cell

Answer 49

true

Question 50

only _ has glucose-6-phosphatase (present in the ER)

Answer 50

liver

Question 51

muscle cells do not have glucose-6-phosphatase so _ stays

Answer 51

glucose-6P

Question 52

small amount of glycogenolysis via _

Answer 52

lysosomal alpha-1,6 glucosidase (acid maltase)