glycogen metabolism I

Question 1

glycogen

Answer 1

long chain homopolymer of glucose molecules with branches

Question 2

glucose molecules within linear chain linked together via

Answer 2

alpha-1,4 glycosidic bonds

Question 3

branch points between glucose monomers of separate chains are formed via

Answer 3

alpha-1,6 glycosidic bonds

Question 4

non-reducing ends contain

Answer 4

a terminal glucose with a free hydroxyl group at carbon 4

Question 5

reducing end consists of glucose monomer connected to a protein called

Answer 5

glycogenin

Question 6

glycogenin creates a short glycogen polymer on itself and serves as a

Answer 6

primer for glycogen synthesis

Question 7

glycogen is degraded and extended from

Answer 7

non-reducing ends

Question 8

glycogen is stored in

Answer 8

liver, muscle, and other tissues

Question 9

glycogen is stored as

Answer 9

granules

Question 10

granules contain not only glycogen but also

Answer 10

the enzymes needed for glycogen metabolism

Question 11

function of liver glycogen

Answer 11

regulates blood glucose levels

Question 12

function of muscle glycogen

Answer 12

provides reservoir of fuel (glucose) for physical activity

Question 13

regulation of glycogen metabolism

Answer 13

allosteric control

covalent modification through reversible phosphorylation of key enzymes

hormonal control

Question 14

glycogenesis

Answer 14

synthesis of glycogen

Question 15

3 key steps of glycogenesis

Answer 15

trapping and activation of glucose

elongation of a glycogen primer

branching of glycogen chains

Question 16

rate limiting enzyme of glycogenesis

Answer 16

glycogen synthase (catalyzes transfer of glucose from UDP-glucose to non-reducing end of glycogen chain)

forms an alpha-1,4 glycosidic bond between glucose molecules

Question 17

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

Answer 17

11

alpha-1,6 link by glucosyl (4:6) transferase

Question 18

what does branching achieve

Answer 18

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

increases rate at which glycogen can be synthesized and degraded

Question 19

a new branch point must be at least _____ residues away from a preexisting branch

Answer 19

4

Question 20

glycogenolysis overview pathway

Answer 20

glycogen –> glucose 1-phosphate (via glycogen phosphorylase) –> glucose 6-phosphate (via phophoglucomutase) –> free glucose can enter glycolysis (muscle/brain), free glucose can enter blood (for use by other tissues), or can enter pentose phosphate pathway (resulting in ribose and NADPH)

Question 21

glycogenolysis in liver

Answer 21

glycogen –> glucose 1-P (via glycogen phosphorylase with co-factor vitamin B6) (rate limiting step) –> glucose 6-P (via PGM) –> glucose (via glucose 6-phosphatase) –> free glucose released into blood to maintain blood glucose

Question 22

glycogenolysis in muscle

Answer 22

glycogen –> glucose 1-P (via glycogen phosphorylase with co-factor vitamin B6) (rate limiting step) –> glucose 6-P (via PGM) –> pyruvate (via glycolysis) –> pyruvate kept in muscle to produce ATP

Question 23

4 key enzymes of glycogenolysis:

Answer 23

1. glycogen phosphorylase (rate limiting step): degrade glycogen to glucose 1-P)
2. debranching enzyme transferase: transfers a block of 3 of the remaining 4 glucose residues to the non-reducing end of the main chain forming an alpha-1,4 bond
3. alpha-1,6-glucosidase: cleaves the alpha-1,6 bond of the single remaining glucose residue to release the free glucose
4. converts glycogen breakdown product suitable for further metabolism (glucose 6-Phosphatase or PGM)????

Question 24

phosphorolysis of glucose residues (via glycogen phosphorylase) continues until GP gets within

Answer 24

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

Question 25

glycogen phosphorylase (GP) adds an ________ and releases a glucose residue as ________

Answer 25

orthophosphate

glucose 1-P

Question 26

cofactor required for glycogen phosphorylase (GP)

Answer 26

pyridoxal phosphate (vitamin B6)

Question 27

phosphoglucomutase

Answer 27

converts glucose 1-P to glucose 6-P

Question 28

how does phosphoglucomutase (PGM) work

Answer 28

a phosphoryl group is transferred from the enzyme to the substrate, and a different phosphoryl group is transferred back to restore the enzyme to its initial state

Question 29

debranching enzyme transferase

Answer 29

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

Question 30

debranching enzyme or alpha-1,6-glucosidase

Answer 30

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

Question 31

glucose 6-Phosphatase is present in ____ cells not in ____ cells

Answer 31

liver

muscle

Question 32

small amount of glycogenolysis occurs in lysosome via

Answer 32

lysosomal alpha-1,6 glucosidase (acid maltase)

Question 33

defect in acid maltase (lysosomal alpha-1,6 glucosidase)

Answer 33

pompe disease

Question 34

glycogenolysis yields ____ glucose 1-P to every ____ free glucose

Answer 34

10

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