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BIOL 2421 - Cellular Biochem > 17. regulation of glycolysis and GNG > Flashcards

17. regulation of glycolysis and GNG Flashcards

1
Q

how can flux through enzyme catalyzed pathways be modulated

A

changes in the number of enzyme molecules or changes in the catalytic activity of the enzyme molecules

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2
Q

T or F: a protein has an infinite lifetime

A

false; it has a finite lifetime

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3
Q

is rapid turnover energetically favorable?

A

no; it is energetically expensive, but it allows more rapid changes in steady state levels for quicker responses to new cellular conditions

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4
Q

how many glucose transporters do humans have

A

12

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5
Q

what are glucose transporters used for

A

regulate the passive intake of glucose from the blood into the cell at different rates and in different tissues

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6
Q

what is the average glucose concentration in blood plasma

A

4-8mM

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7
Q

where does GLUT1 have high expression

A

erythrocytes

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8
Q

where does GLUT1 have low expression

A

most tissues

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9
Q

where is GLUT3

A

brain

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10
Q

what does GLUT3 represent

A

basal glucose uptake

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11
Q

where is GLUT2 present

A

liver and pancreatic beta cells

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12
Q

what does low Kt represent

A

low Kt= high affinity to glucose

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13
Q

which GLUT (1-3) has the lowest Kt, and which has the highest

A

GLUT3 has low Kt (since it’s the basal glucose uptake). GLUT2 has a higher Kt

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14
Q

why is it significant that GLUT have different Kt values

A
  • muscle glucose is for making ATP for contraction
  • liver glucose will be stored as glycogen
  • at basal levels, lots of gluc will be moving through transporters, and GLUT1 is more effective than GLUT2, but because of the Kt GLUT2 has the ability to respond to glucose changes better than GLUT1
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15
Q

which transporter is involved with insulin

A

GLUT4

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16
Q

where is insulin released from

A

the pancreas

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17
Q

what happens to GLUT4 when insulin is released

A

GLUT4 transporters move from intracellular vesicles to the PM to passively move glucose into adipocytes and myocytes

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18
Q

T or F; we need to make sure the distinct enzymes in a paired pathway aren’t working at the same time

A

true

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19
Q

are paired pathways reversible or irreversible? why

A

irreversible; an enzyme converts one thing to another, and then a different enzyme converts that back into the starting product

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20
Q

which enzymes in glycolysis regulate flux: the ones the two share, or the ones they don’t share

A

only the ones they don’t share are able to regulate flux

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21
Q

how many hexokinase isozymes do humans have

A

4

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22
Q

which hexokinase isozyme is the main myocyte isozyme

A

hexokinase II

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23
Q

describe the Km for hexokinase II

A

very low Km (0.1mM)

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24
Q

what inhibits hexokinase

A

glucose 6-phosphate

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25
Q

why does glucose 6-phosphate inhibit hexokinase

A

hexokinase is the enzyme that converts glucose to glucose 6-phosphate in glycolysis. So having more product means less product needs to be made, which means hexokinase is inhibited

26
Q

where is hexokinase IV present

A

the liver

27
Q

what is the name of hexokinase IV

A

glucokinase

28
Q

describe the Km of hexokinase IV

A

high Km (10mM)

29
Q

is hexokinase IV inhibited by G6P

A

no

30
Q

why isn’t hexokinase IV inhibited by G6P

A

in the liver, we aren’t consuming glucose, but we’re maintaining glucose homeostasis by building up or breaking down glycogen stores. The high Km (low glucose affinity) allows the liver to regulate blood glucose levels after a meal or a fast

31
Q

describe what happens when blood glucose levels increase (in regards to GLUT and hexokinase)

A

influx of glucose to the liver due to GLUT2, hexokinase IV works faster as glucose concentration rises, glucose is converted to G6P which cannot leave the cell and will be funneled into glycogen synthesis

32
Q

describe what happens when blood glucose levels decrease (in regards to GLUT and hexokinase)

A

glucose is low relative to the hexokinase IV Km. Low enzyme velocity. Any glucose that is released from glycogen is not going to be phosphorylated, so it leaves the cell to raise blood glucose levels

33
Q

describe hexokinase IV inhibition during a fast

A

F6P promotes hexokinase movement into the nucleus to it can’t do it’s job

34
Q

describe hexokinase activity after a meal

A

glucose promotes the removal of the regulatory protein so the hexokinase can return to the cytosol and produce G6P

35
Q

describe the effect of ATP concentration on hexokinase

A

high ATP = reduced hexokinase transcription

36
Q

what is the commitment step of glycolysis (and what enzyme is used)

A

F6P –> F1,6P

enzyme used: phosphofructokinase-1

37
Q

describe the structure of PFK1

A

a homotetramer, where each subunit has a catalytic site and a binding site for allosteric regulators

38
Q

what inhibits PFK1

A

ATP

39
Q

how does ATP inhibit PFK1

A

it binds to the allosteric site and lowers its affinity for F6P

40
Q

describe the effect of citrate of PFK1 activity

A

citrate inhibits PFK1: it’s in the CAC and it means that ATP will later be produced, and ATP is an inhibitor (which makes both of these inhibitors)

41
Q

since PFK1 was step 3 of glycolysis, which is the corresponding enzyme for GNG (step 8)

A

fructose 1,6-bisphosphatase (FBPase-1)

42
Q

what does FBPase-1 do

A

converts F1,6BP to F6P

43
Q

describe how FBPase-1 is regulated

A

inhibited by AMP to prevent gluconeogenesis when ATP stores are low

44
Q

describe how hormone levels affect PFK1 and FBPase1 at low blood glucose levels

A

glucagon is released by the pancreas which signals the liver to stop consuming glucose and begin producing and releasing it. Glycogen stores broken down and GNG is upregulated. Glucagon ramps up FBP1=F6P=GNG

45
Q

describe how hormone levels affect PFK1 and FBPase1 at high blood glucose levels

A

insulin is released by the pancreas which signals the liver to consume and store glucose. Glycogen stores build up, glycolysis is upregulated. Insulin ramps up PFK1=F1,6BP=glycolysis

46
Q

describe the impact F26BP has on PFK1

A

PFK1 has an increased affinity for its substrate in the presence of F26BP, meaning it has a reduced affinity for its inhibitors (ATP and citrate)

47
Q

describe the impact of F26BP on FBPase-1

A

FBPase-1 has a reduced affinity for its substrate in the presence of F26BP, and it has an increased affinity for its inhibitors (AMP)

48
Q

where does F26BP come from? what synthesizes and degrades it

A

formed from F6P by PFK-2

degraded to F6P by FBPase-2

49
Q

what controls PFK-2 and FBPase-2 levels

A

concentration of glucagon and insulin in the liver

50
Q

describe the structure of PFK-2 and FBPase-2

A

kinda like a conjoined enzyme

51
Q

when the joint enzyme is phosphorylated, which half is active

A

FBPase-2 is active

52
Q

when the joint enzyme is not phosphorylated, which half is active

A

PFK-2 is active

53
Q

how many isozymes does pyruvate kinase have in humans

A

3

54
Q

which two pyruvate kinase isozymes are we focusing on

A

liver (L) and muscle (M)

55
Q

what inhibits pyruvate kinase isozymes

A

ATP, Acetyl-CoA, and fatty acids (all signaling an abundance of energy)

56
Q

what activates the pyruvate kinase isozymes

A

F1,6BP

57
Q

is pyruvate kinase active or inactive when phosphorylated

A

inactive

58
Q

what phosphorylates pyruvate kinase to make it inactive

A

Protein Kinase A

59
Q

what activates Protein Kinase A so it can phosphorylate and inactivate pyruvate kinase

A

glucagon

60
Q

in regards of pyruvate, how is GNG initiated

A

pyruvate is carboxylized to initiate GNG

61
Q

what activates carboxylation of pyruvate to initiate GNG

A

Acetyl-CoA

62
Q

other than activating carboxylation of pyruvate, what does Acetyl-CoA do

A

it inhibits pyruvate oxidation

BIOL 2421 - Cellular Biochem (21 decks)

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