Exam 2 Lecture 17 Glycogen Metabolism I Flashcards

1
Q

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

A

homopolymer

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2
Q

glucose molecules within linear chain linked together via _

A

alpha-1,4 glycosidic bonds

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3
Q

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

A

alpha-1,6 glycosidic bonds

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4
Q

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

A

non-reducing ends (multiple)

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5
Q

_ consists of glucose monomer connected to a protein called glycogenin

A

reducing ends

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6
Q

glycogen is _ and _ from non-reducing ends

A

degraded and extended

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7
Q

glycogen is stored in:

A

liver, muscle, and other tissue

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8
Q

glycogen is stored as _

A

granules

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9
Q

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

A

enzymes needed for glycogen metabolism

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10
Q

defects in glycogen enzymes can lead to disorders termed _

A

glycogen storage disorders

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11
Q

liver glycogen regulates

A

blood glucose levels (sensor)

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12
Q

muscle glycogen provides

A

reservoir of fuel (glucose) or physical activity

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13
Q

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

A

true

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14
Q

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

A

false; synthesis and degradation are INDEPENDENT of each other

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15
Q

Pathways in glycogen metabolism are regulated independently?

A

yes

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16
Q

how does muscle glycogen supply energy

A

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

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17
Q

what are the ways to regulate glycogen metabolism?

A
  1. allosteric control
  2. covalent modification
  3. hormonal control
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18
Q

how does allosteric control regulate glycogen metabolism

A

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

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19
Q

how does covalent modification regulate glycogen metabolism

A

mainly through phosphorylation; reversible

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20
Q

how do hormones regulate glycogen metabolism

A

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

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21
Q

What are the 3 key steps to glycogenesis

A
  1. trapping and activation of glucose
  2. elongation of a glycogen primer
  3. branching of glycogen chains
22
Q

how does trapping of glucose occur?

A

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

23
Q

hows does activation of glucose occur?

A

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)

24
Q

UDP is for _

25
how does elongation occur?
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
26
glycogen synthase forms _ glycosidic bonds between glucose molecules
alpha-1,4
27
how does branching of glycogen chains occur?
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
28
in branching, an alpha-1,4 link is broken off and attached through an _ link
alpha-1,6 link
29
what enzyme is used for branching?
glucosyl (4:6) transferase
30
Branching increases _
solubility of glycogen and increases # of terminal non-reducing ends
31
glycogen degradation aka
glycogenolysis
32
glycogen broken down to release _
glucose-1-phosphate (rate limiting step)
33
_ remodeled to permit further degradation
glycogen remnant
34
in glycogenolysis, glucose-1-phosphate converted to
glucose-6-phosphate
35
glucose-6-phosphate from glycogenolysis can now enter various pathways which are:
1. glycolysis 2. free glucose for release into blood stream 3. pentose phosphate pathway-NADPH and ribose derivative (nucleic acid synthesis)
36
how many key enzymes for glycogenolysis?
4
37
what is the rate limiting enzyme in chain shortening
glycogen phosphorylase (GP) catalyzes the cleavage of glycogen
38
chain shortening occurs at the _ end of the polymer
non-reducing end
39
GP adds an _ and releases a glucose residue as glucose-1-phosphate
orthophosphate
40
GP uses _ as a cofactor
pyridoxal phosphate (Vit B6)
41
phosphorolysis of glucose residues continues until the GP gets within _
4 residues of the alpha-1,6 linkage of a branch point
42
what does the phosphoglucomutase step do and how does it work?
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
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
transferase
44
the debranching enzyme _ cleaves the alpha-1,6 bond of the single remaining glucose residue to release the free glucose
alpha-1,6 glucosidase
45
in release of glucose, glucose is phosphorylated by _
hexokinase
46
together, transferase and alpha-1,6 glucosidase convert _ glycogen into a _ structure for further action by GP
convert branched glycogen into a linear structure
47
in debranching, _ cuts at non-reducing end
phosphorylase
48
in debranching of glycogen, yields _ G1P to 1G
10 G1P to 1G
49
T/F: glucose-6P cannot get out of the cell
true
50
only _ has glucose-6-phosphatase (present in the ER)
liver
51
muscle cells do not have glucose-6-phosphatase so _ stays
glucose-6P
52
small amount of glycogenolysis via _
lysosomal alpha-1,6 glucosidase (acid maltase)