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Chapter 15 > Regulation of Glycolysis > Flashcards

Regulation of Glycolysis Flashcards

1
Q

when we are looking for the key steps that are important for the regulation of glycolysis we can look at 3 key things what are they?

A
  1. show irreversibility based on delta G and single arrows : the ones that are plus or minus 10. the in vivo numbers are better than in vitro , if its irreversible its probably a key step
  2. is it capable of being allostericly modified : if yes its a potential key step
  3. are the modifiers present: if the modifiers are able to actually modify the enzyme
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2
Q

what is the rate determining step of glycolysis

A

-PFK is the rate determine step because of delta g and it has the most present modifiers

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3
Q

how many irreversible steps are there is glycolysis

A
  • there are 3 irreversible steps in glycolysis
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4
Q

list 3 allosteric activators of the rate determining enzyme pfk

A

ADP, AMP, F26P - activators

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5
Q

list an inhibitor of pfk

A

ATP

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6
Q

Will ATP shift a PFK to the R or T state?

A

ATP will shift things to the t state

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7
Q

will the activators of PFK shift it to the R or T state

A

R state

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8
Q

does F6P bind to the R or T state of PFK

A

R

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9
Q

Why can ATP bind to T and R state

A

ATP is both a substrate and an allosteric inhibitor.

The substrate site binds ATP equally well in either conformation
Inhibitor site binds ATP almost exclusively in the T state.

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10
Q

How many binding sites does PFK have for ATP?

A

Each PFK subunit has two binding sites for ATP: a substrate site and an inhibitor site.

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11
Q

List 3 compounds that reverse the inhibitory effects of ATP on PFK

A

Other compounds, including ADP, AMP, and fructose-2,6-bisphosphate (F2,6P), reverse the inhibitory effects of ATP and are therefore activators of PFK.

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12
Q

Does the inhibitor site bind ATP in the T or R state?

A

Inhibitor site binds ATP almost exclusively in the T state.

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13
Q

What effect do high concentrations of ATP have on glycolysis/ PFK?

A

At high concentrations, ATP acts as an allosteric inhibitor of PFK by binding to the T state

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14
Q

what is the effect of Shifting the T to R equilibrium in favor of the T state on pfk

A

Shifting the T to R equilibrium in favor of the T state and thus decreasing PFK’s affinity for F6P

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15
Q

Describe what a graph looks like with high concentrations of ATP on PFK.

A

In graphical terms, high concentrations of ATP shift the curve of PFK activity versus [F6P] to the right and make it even more sigmoidal (cooperative)

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16
Q

describe what an activator such as ADP or AMP does to the confirmational state of PFK

A

An activator such as AMP or ADP counters the effect of ATP by binding to R-state PFK, thereby shifting the T to R equilibrium toward the R state.

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17
Q

Does more ATP shift the PFK graph to the left or the right?

A

the right

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18
Q

is pfk inhibited when ATP is high or low?

A

When [ATP] is high as a result of low metabolic demand, PFK is inhibited and flux through glycolysis is low; [ATP] is low, flux through the pathway is high and ATP is synthesized to replenish the pool

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19
Q

what is substrate cycling

A

Known as a substrate cycle because it cycles a substrate to an intermediate and back again. It functions to decrease the minimum flux. The substrate is put into a “holding pattern.”

20
Q

is PFK exergonic or endergonic

A

PFK: is highly exergonic (ΔG = –25.9 kJ · mol–1)

21
Q

list 2 things that will stop the inhibition of PFK by ATP.

A

Inhibition of PFK by ATP is relieved by AMP as well as ADP. This results from AMP’s preferential binding to the R state of PFK

22
Q

What reaction will amplify the PFK activity if the decrease in ATP is too small

A

A metabolic signal consisting of a decrease in [ATP] too small to relieve PFK inhibition is amplified significantly by the adenylate kinase reaction, which increases [AMP] by an amount that produces a much larger increase in PFK activity.

23
Q

what does substrate cycling actually cycle?

A

Known as a substrate cycle because it cycles a substrate to an intermediate and back again.

24
Q

is substrate cycling a futile process

A

Not at all “futile” but, rather, has a regulatory function

25
Q

what 2 things control substrate cycling ?

A

The rate of substrate cycling itself may be under hormonal or neuronal control so as to increase the sensitivity of the metabolic system under conditions when high activity (fight or flight) is anticipated.

26
Q

what two enzymes are an example of substrate cycling ?

A

F6P and FBP

27
Q

describe what substrate cycling looks like in resting muscle

A

In resting muscle, both enzymes in the F6P/FBP substrate cycle are active, and glycolytic flux is low.

28
Q

What does substrate cycling look like in active muscle

A

In active muscle, PFK activity increases while FBPase activity decreases. This dramatically increases the flux through PFK and therefore results in high glycolytic flux.

29
Q

why is PFK the rate determining step

A

most negative delta g, has most modifiers, has most modifiers present

30
Q

List the 3 activators of PFK

A

ADP, AMP, and fructose-2,6-bisphosphate (F2,6P), reverse the inhibitory effects of ATP and are therefore activators of PFK.

31
Q

list the 2 inhibitors of PFK

A

citrate and ATP

32
Q

When pfk is inhibited is is in the t state or the r state

A

t state

33
Q

how many binding sites does PFK have for ATP

A
  1. Each PFK subunit has two binding sites for ATP: a substrate site and an inhibitor site.
34
Q

t/f ATP can bind in either the T state or the R state

A

The substrate site binds ATP equally well in either conformation

35
Q

Is F26P s substrate of glycolysis ?

A

no

36
Q

what is the most potent activator of PFK

A

f2 6p

37
Q

T/F ATP can bind to PFK regardless of T or R state

A

true

38
Q

if PFK is in the T state can ATP bind to the substrate site

A

yes

39
Q

if PFK is in the T state can ATP bind to the allosteric site

A

yes

40
Q

if PFK is in the R state can ATP bind to the substrate site

A

no

41
Q

if PFK is in the R state can ATP bind to the allosteric site

A

yes

42
Q

if PFK is in the T state would F6P be able to bind to substrate binding site

A

yes , because F6P is a substrate . And if we are following the rules of allostery it will be able to bind. But since ADP is not a substrate it has to be only in the R state in order to bind.

43
Q

does it take ATP to do substrate cycling ?

A

yes , it is like an engine in idle

44
Q

why would we use substrate cycling?

A

if we see a delta g reaction around 10 we can assume that it is reversible . this means that if we go from a to b we can use the same enzyme. but if the number is greater than ten then we can not use the same enzyme to go backwards in the reaction because the reaction is not reversible.

45
Q

what are 3 steps in glycolysis that we could use substrate cycling

A

There are 3 steps where this theory is able to be applied. This theory can be applied in: PGI - it is so negative that we will need another reaction system. Hexokinase, PFK and PK. According to the delta g’s of these reactions we would need to use substrate cycling in order to take the reaction backwards.

46
Q

what enzyme does pfk use to do substrate cycling?

A

Fructose-1,6-bisphosphatase (FBPase) which is present in many mammalian tissues catalyzes the exergonic hydrolysis of FBP (ΔG = –8.6 kJ · mol–1).

Chapter 15 (5 decks)

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