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Biochemistry (material for exam II) > Glycogen Metabolism > Flashcards

Glycogen Metabolism Flashcards

1
Q

Osmotically inactive and readily mobilized form of glucose

A

Glycogen

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2
Q

Glycogen is a branched long chain _______ of glucose molecules

A

Homopolymer

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3
Q

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

A

12, 55,000

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4
Q

In glycogen glucose is linked together via _____

A

alpha 1-4 glycosidic bonds

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5
Q

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

A

12, via alpha 1,6 glycosidic bonds

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6
Q

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

A

C4

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7
Q

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

A

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

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8
Q

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

A

primer

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9
Q

Glycogen is stored in the

A

liver, muscle, and other tissues

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10
Q

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

A

Granules

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11
Q

What is the function of liver glycogen

A

regulates overall blood glucose levels

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12
Q

What is the function of muscle glycogen

A

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

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13
Q

pathways for glycogen synthesis and degradation are regulated

A

independently

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14
Q

What are some modes of regulation of glycogen synthesis and degradation

A

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

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15
Q

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

A

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

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16
Q

What are the names of the key enzymes in glycogenolysis

A

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

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17
Q

What is the rate limiting step of glycogenolysis

A

Glycogen phosphorylase (GP)

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18
Q

Where does glycogen phosphorylase (GP) shorten the chain

A

at the non-reducing end of glycogen polymer

19
Q

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

A

Orthophosphate

20
Q

Glycogen phosphorylase (GP) uses what as a cofactor

A

Pyridoxal phosphate (vitamin B6)

21
Q

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

A

4

22
Q

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

A

Transferase

23
Q

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

A

Debranching enzyme/ alpha-1,6- glucosidase

24
Q

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

A

hexokinase

25
Q

What is the function of phosphoglucomutase

A

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

26
Q

Glucose 6-Phosphatase is only located in

A

The liver

27
Q

What is the function of glucose 6-phosphatase

A

it converts Glucose 6-Phosphate into glucose

28
Q

Glycogen phosphorylase is regulated by

A 
several allosteric effectors (signal energy state of the cell) 
reversible phosphorylation (responsive to hormones)
29
Q

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

A

liver, muslce

30
Q

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

A

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

31
Q

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

A

glucose

32
Q

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

A

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)

33
Q

What are negative allosteric regulators of glycogen phosphorylase

A

ATP and glucose 6-P

34
Q

The conversion of glycogen phosphorylase a to b is initiated by

A

hormones

35
Q

Phosphorylase kinase becomes active with

A

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

36
Q

Phosphorylase kinase has 4 subunits what are they

A

(alpha, beta, gamma, delta)x4

37
Q

Phosphorylase Kinase is a large protein of about

A

1300kD

38
Q

What are the subunits of phosphorylase kinase

A

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

39
Q

Epinephrine and glucagon do what to glycogen

A

induce glycogen breakdown

40
Q

glucagon and epinephrine work through

A

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

41
Q

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

A

isozymes

42
Q

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

A

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)

43
Q

Mutation in the liver glycogen phosphorylase results in

A

Hers disease

44
Q

Mutation in the muscle glycogen phosphorylase results in

A

McArdle syndrome

Biochemistry (material for exam II) (10 decks)

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