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Biochemistry II > Regulation of Glycolysis & Gluconeogenesis > Flashcards

Regulation of Glycolysis & Gluconeogenesis Flashcards

1
Q

How is short-term regulation accomplished?

A

Changes in enzymatic activity

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2
Q

How can the activity of an enzyme be altered? We discussed four ways in lecture.

A
  1. Allostery
  2. Covalent modification
  3. Substrate concentration change
  4. Compartmentalization
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3
Q

What is allosteric regulation?

A

Regulation that occurs as a result of some small molecule that inhibits or activates an enzyme by binding somewhere besides the enzyme’s active site

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4
Q

What types of covalent modifications are common in regulation?

A

Phosphorylation

Methylation

Acetylation

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5
Q

What amino acid residues are most often targeted for phosphorylation?

A

Serine

Tyrosine

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6
Q

How does the change in substrate concentration regulate an enzyme’s activity?

A

When [S] ≤ km a change in substrate concentration will affect the rate

When [S] >>> km changes in substrate concentration are unlikely to affect the rate as it is insensitive to substrate concentration changes

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7
Q

How is long-term regulation accomplished in the cell?

A

Changing the rate of synthesis and degradation of specific enzymes in the pathway

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8
Q

What do we mean by compartmentalization?

A

The enzyme and substrate are separated usually via binding to a regulatory protein

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9
Q

What is vmax equal to?

A

vmax = kcat [E]total

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10
Q

What is kcat?

A

Catalytic constant

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11
Q

If the enzyme concentration increases, what happens to vmax?

A

vmax increases

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12
Q

Expression of a gene is controlled by specific sequences in the DNA that are recognized by _________________ ______________.

A

Transcription factors

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13
Q

To what do transcription factors bind?

A

Response elements near the promoter

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14
Q

What do transcription factors generall do?

A

Increase or decrease transcription of a particular gene

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15
Q

_________________________ is also involved in long-term regulation and is associated with the stability of mRNA, translation rate, and protein turnover.

A

Degradation

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16
Q

The regulation of glycolysis and gluconeogenesis occurs at the three ____________________ steps in the pathways.

A

Irreversible

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17
Q

In what manner are the three irreversible steps in glycolysis and gluconeogenesis regulated?

A

A reciprocal manner

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18
Q

The three irreversible steps of glycolysis and gluconeogenesis operate far from or close to equilibrium?

A

Far from

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19
Q

How are reactions in metabolic pathways that operate near equilibrium regulated?

A

Changes in substrate and product concentration - Le Chatelier’s Principle

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20
Q

What is the first major point of (enzymatic) regulation discussed in class?

A

Hexokinase and glucose-6-phosphatase

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21
Q

Which hexokinase is distributed mainly in muscle tissue?

A

Hexokinase II

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22
Q

What hexokinase is distributed in the liver?

A

Hexokinase IV or glucokinase

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23
Q

Hexokinase IV is also known as ______________________ and resides in the liver.

A

Glucokinase

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24
Q

There are several different forms or __________________________ of hexokinase in the human genome; these forms have different affinities for their substrates as well as different regulatory components.

A

Isozymes

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25
Q

Based on the following Michaelis-Menten plot, what are the approximately km values for hexokinase and glucokinase?

A

Hexokinase ~ 0.25 mM

Glucogkinase ~6 mM

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26
Q

Hexokinase has a much lower km value for glucose than does glucokinase. Why?

A

A low km means that an enzyme has a higher affinity for a substrate; in the muscle, we want hexokinase to trap glucose in the cell for usage. This means that we want hexokinase II to have a low km or a high affinity for glucose.

In the liver, we want to release glucose into the bloodstream and thereby maintain blood glucose concentrations. This means that we want glucokinase to have a high km or a low affinity for glucose.

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27
Q

The vmax of hexokinase II occurs at _____ (low or high) concentrations of glucose.

A

Low

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28
Q

The vmax of glucokinase occurs at _______ (low or high) concentraitons of glucose.

A

High

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29
Q

Which enzyme - hexokinase II or hexokinase IV/glucokinase - is inhibited by glucokinase regulatory protein?

A

Glucokinase IV/hexokinase IV

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30
Q

What are the five characteristics of hexokinase II discussed in class?

A
  1. Tissue distribution - in muscle (mainly)
  2. km - ~0.25 mM (glucose)
  3. vmax - occurs at low concentrations of glucose
  4. Inhibition by G6P - yes (allostery)
  5. Inhibition by glucokinase regulatory protein - no
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31
Q

Which enzyme - hexokinase II or hexokinase IV/glucokinase - is inhibited by glucose-6-phosphate?

A

Hexokinase II

32
Q

What is the biological significance of the differences between hexokinase II and hexokinase IV/glucokinase?

A

Muscle is a consumer of glucose; hexokinase’s role is to maintain the glucose concentration in the cell so that it can be consumed for energy.

Liver maintains glucose concentrations in the blood; the liver needs to send glucose out of the cell; it has a higher km so as to prevent the phosphorylation of glucose, which would trap glucose in the cell

33
Q

Glucokinase is also regulated by _______________________.

A

Compartmentalization

34
Q

At high concentrations of fructose-6-phosphate, the regulatory protein ______________________ _______________ _____________ (GKRP) binds to glucokinase and sequesters it within the nucleus.

A

Glucokinase regulatory protein

35
Q

Why do we want glucokinase sequestered at high levels of fructose-6-phosphate?

A

In the liver, high levels of fructose-6-phosphate indicate that the glucose concentration has decreased outside of the cell - we need to sequester glucokinase so that any incoming glucose remains unphosphorylated and free to exit the cell and stabilize blood glucose levels

36
Q

Why do we want glucokinase active at high levels of glucose?

A

In the liver, high levels of glucose suggest that there is too much glucose in the blood, we we want to release glucokinase and phosphorylate glucose, trapping it in the cell and thus returning blood glucose levels to normal.

37
Q

What glucose transporter is present in the liver?

38
Q

At ________________ (high or low) cellular glucose concentrations, glucokinase moves into the cytosol and becomes active. At ____________________ (high or low) cellular glucose concentrations, glucokinase regulatory protein binds glucokinase and sequesters it in the nucleus.

39
Q

At ______________________ (high or low) levels of fructose-6-phosphate, glucokinase is active.

At ____________________ (high or low) levels of fructose-6-phosphate, glucokinase is inactive and sequestered in the nucleus.

40
Q

Glucose-6-phosphatase is not under allosteric control. Instead it is controlled by concentrations of _________________________.

A

Glucose-6-phosphate

41
Q

If the concentraiton of glucose-6-phosphate increases in the liver, what happens to the activity levels of glucose-6-phosphatase?

A

It increases; we want to produce glucose to leave the cell

42
Q

When is synthesis of glucose-6-phosphatase induced?

A

When blood glucose levels drop

43
Q

Glucose-6-phosphatase is under what hormone’s control?

44
Q

What is the second major point of regulation discussed in class (AKA THE MAJOR REGULATION STEP)?

A

Phosphofructokinase-1 and fructose-1,6-bisphosphatase-1

45
Q

What is the committed step of glycolysis?

A

The transformation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1

46
Q

Why can’t PFK-1 and FBPase-1 operate at the same time?

A

Because the sum of the two steps is ATP + H20 –> ADP + Pi; it is energetically wasteful and futile

47
Q

What is the energy status of the cell related to?

A

Concentrations of ATP and AMP

48
Q

High ATP levels indicate that the cell is energy _____________.

49
Q

High AMP levels indicate that the cell is energy ___________.

50
Q

Which is a better indicator of the cell’s energy status: ATP or AMP?

51
Q

How does ATP affect the activity of PFK-1?

A

ATP is an allosteric inhibitor of PFK-1

52
Q

______________________ kinetics indicate allostery.

53
Q

How does fructose-2,6-bisphosphate affect the activity of PFK-1?

A

F26BP is an allosteric activactor of PFK-1

54
Q

______ is an allosteric inhibitor of PFK-1 while ____ is an allosteric activator of PFK-1 for its substrate fructose-6-phosphate.

55
Q

How do ATP and F26BP act as allosteric modulators of PFK-1?

A

They decrease or increase the affinity of PFK-1 for F6P

ATP decreases affinity; F26BP increases affinity

56
Q

How does F26BP affect the activity of FBPase-1?

A

F26BP is an allosteric inhibitor of FBPase-1

57
Q

____________ is an allosteric inhibitor of fructose-1,6-bisphosphatase-1, lowering its affinity for the substrate, fructose-1,6-bisphosphate.

A

Fructose-2,6-bisphosphate

58
Q

What are three activators of PFK-1?

A
  1. F26BP
  2. AMP
  3. ADP
59
Q

What are two inhibitors of PFK-1?

A
  1. ATP
  2. Citrate
60
Q

What are activators for FBPase-1?

A

None were discussed

61
Q

What are two inhibitors of FBPase-1?

62
Q

Where does fructose-2,6-bisphosphate come from?

A

It is derived from the phosphorylation of fructose-6-phosphate by phosphofructokinase-2

63
Q

PFK2 and FBPase-2 are part of a _______________ enzyme.

A

Bifunctional

64
Q

When is the FBPase-2 activity of PFK2/FBPase2 “on”?

A

When the enzyme is phosphorylated

65
Q

When is FBPase-2 activity of PFK2/FBPase 2 “off”?

A

When the enzyme is dephosphorylated

66
Q

What enzyme catalyzes the hydrolysis of fructose-2,6-bisphosphate to fructose-6-phosphate?

A

Fructose-2,6-bisphosphatase-2

67
Q

The concentration of ________________________________ is critically important for the regulation of glucose metabolism; its concentration is regulated by hormonal signaling pathways

A

Fructose-2,6-bisphosphate

68
Q

The third major point of regulation involves pyruvate kinase versus _________________ _______________ and PEP carboxykinase.

A

pyruvate carboxylase

69
Q

_____________ ____________ exists in different forms depending upon tissue type.

A

Pyruvate kinase

70
Q

In all tissue types, what four molecules inhibit pyruvate kinase?

A
  1. ATP
  2. Acetyl-CoA
  3. Long-chain fatty acids
  4. Alanine
71
Q

In the liver isoform, pyruvate kinase is also regulated by ______________________ ________________.

A

Covalent modification

72
Q

What does phosphorylation by PKA of pyruvate kinase in the liver accomplish?

A

Inactivation of pyruvate kinase

73
Q

Pyruvate carboxylase is regulated by ATP. High levels of ATP are _________________.

A

Stimulatory

74
Q

PEP carboxykinase is regulated transcriptionally via the glucagon and insulin signals. What does each signal cause?

A

Glucagon increases transcription of PEP carboxykinase

Insulin decreases transcription of PEP carboxykinase

Biochemistry II (19 decks)

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