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Biocheem > Lecture 26 > Flashcards

Lecture 26 Flashcards

1
Q

What is the change in free energy?

A

The free energy that is associated with the free energy of products minus free energy of reactants

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2
Q

What is 𝛥Gº?

A

The standard free energy change in the chemical standard state

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3
Q

What is 𝛥Gº’ ?

A

The change in free energy of the biochemical standard state

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4
Q

What does 𝛥Gº take into account?

A

Things like protons and water

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5
Q

What does the actual free energy change deal with?

A

The actual concentrations of the reactants and products for a given reaction but not standard concentrations that is usually 1 molar for reactants and products

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6
Q

Why is actual free energy change more important than standard free energy?

A

Because in real situations were never at the standard state

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7
Q

When is standard free energy change useful?

A

Reactions in terms of stability of products vs substrates

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8
Q

What are the conditions of the the biochemical standard state?

A
  • pH = 7
  • [S] & [P] = 1M
  • Temperature = 25ºC/298K
  • Pressure = 1 atm
  • [H2O] = 55M
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9
Q

What is the proton concentration in the biochemical state?

A

10^-7 molar

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10
Q

Why is the [H2O] = 55M in the biochemical standard state?

A

Because that is the amount found in a unit volume

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11
Q

What do we exclude from biochemical reaction calculations and why?

A
  • [H+]
  • [H2O]
  • Because we assume they’re not changing much
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12
Q

What must the actual free energy change be for a reaction to proceed?

A

It must be negative

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13
Q

What must the characteristics of the standard free energy change be for a reaction to proceed?

A

It doesn’t necessarily have to be negative for a reaction to proceed

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14
Q

What must be negative for a reaction to proceed?

A

𝛥G’ is negative - Actual free energy change is negative

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15
Q

What does Exergonic mean?

A

𝛥G’ (actual free energy change) is negative and the reaction is spontaneous

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16
Q

What can be used to represent the symbols of actual free energy change?

A

𝛥G’

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17
Q

What determines if a reaction is going to proceed in the forward or reverse direction?

A

Actual free energy change

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18
Q

What does it mean if free energy is greater than zero (𝛥G > 0)?

A

A reaction will not occur in the forward direction, it will proceed backwards so that substrates are favored

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19
Q

What does it mean if free energy is less than zero (𝛥G < 0)?

A

Reaction will occur spontaneously

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20
Q

When will a reaction be considered irreversible?

A

𝛥G &laquo_space;0

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21
Q

When is reaction considered reversible?

A

When 𝛥G ~ 0

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22
Q

What is an irreversible reaction?

A

One where the free energy change is always negative under cellular conditions

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23
Q

Which types of reactions are more encountered in metabolic pathways?

A

Reversible reactions

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24
Q

What does it mean if actual free energy (𝛥G) is close to zeroe?

A

The system is close to equilibrium, and the reaction can be reversible

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25
Q

What is 𝛥G?

A

The chemical actual free energy change

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26
Q

What is 𝛥G’?

A

The biochemical actual free energy change

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27
Q

What is 𝛥Gº’?

A

The actual free energy of the biochemical standard state

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28
Q

What is 𝛥G’?

A

The biochemical actual free energy change

29
Q

What may change the the direction of the reaction in reversible reaction?

A

Changes in concentration of either the reactants or products

30
Q

What happens as the concentration of C in a reversible reaction is increased?

A

The second term becomes more positive and the free energy change will also become more positive and the reaction will proceed in the reverse direction

31
Q

What happens as the concentration of B in a reversible reaction is increased? (B ➡️ C)

A

The second value in the equation becomes smaller and the terms becomes less positive or more negative and the actual free energy then becomes negative and the reaction proceeds in the forward direction

32
Q

What happens to the actual free energy if Q is increased (less reactants more products)?

A

The actual free energy becomes less negative

33
Q

What should 𝛥G (actual free energy) be equal to at equilibrium?

A

It should be equal to 0

34
Q

What should Q be equal to at equilibrium?

A

K

35
Q

What does it mean in terms of reactants and products if the actual free energy change is more negative?

A

This means the reaction is more spontaneous so there are more reactants to drive the products. Because looking at Q, the ratio of products to reactants, there are more reactants on the bottom meaning that Q is smaller and the whole term is smaller

36
Q

What are metabolic pathways?

A

A series of enzyme-catalyzed chemical reactions

37
Q

When will a metabolic pathway proceed?

A

When the free energy change overall is negative ie. exergonic

38
Q

In a metabolic pathway (A→B↔C↔D→E) what are the concentrations of intermediates?

A

A and E change but B, C, and D are relatively stable

39
Q

Which steps in metabolism are usually regulated?

A

Irreversible steps are usually regulated

40
Q

What is the rate-limiting step in a pathway?

A

The irreversible, regulated reaction that determines the overall rate of the pathway

41
Q

What is product inhibition?

A

When an enzyme is inhibited by the product of its reaction

42
Q

What is feedback inhibition?

A

When an enzyme is inhibited by a metabolite further down the pathway

43
Q

What is feedback inhibition an example of?

A

Negative heteroallostery

44
Q

What is feed-forward activation?

A

When an enzyme may be activated by a metabolite upstream

45
Q

What is feed forward activation an example of?

A

Positive heteroallostery

46
Q

What kind of allostery is product inhibition?

A

It is heteroallostery

47
Q

What is the reciprocal pathway to glycolysis?

A

Gluconeogenesis

48
Q

What is added in reciprocal regulation?

A

Different enzymes that may consume ATP to catalyze the reverse reaction

49
Q

What is the free energy change of reversible reactions?

A

About 0

50
Q

What is the direction of reversible reactions dependant on?

A

The concentration of the substrates and products

51
Q

What aren’t usually the point of control in a metabolic pathway?

A

Reversible reactions

52
Q

Do reversible reactions use enzymes?

A

Yes

53
Q

What contributes to metabolic pathways acting at a steady state?

A
  • biological reactions being reversible
  • key reactions at the beginning and end of a pathway are often regulated synchronously
  • reversible reactions proceed to equilibrium
54
Q

When are catabolic pathways active?

A

When cellular energy levels are low

55
Q

What are high energy intermediates?

A

Compounds which contain usable chemical energy

56
Q

What is the criteria for high energy intermediates?

A
  • Energy can be recovered or used

* Simple reaction associated with large 𝛥G (20kJ/mol released)

57
Q

What are the three major types of high energy intermediates?

A
  • Electron carriers
  • Nucleotide triphosphates
  • Thioesters
58
Q

What are examples of electron carriers?

A
  • NADH
  • NADPH
  • FADH2
  • FMNH2
59
Q

What are the electron acceptors?

A

NAD+, NADP+, FAD and FMN

60
Q

What are examples of nucleotide triphosphates?

A

ATP, UTP, GTP

61
Q

Why are NTPs considered high energy molecules?

A

Because of the phosphoanhydride bond

62
Q

What are the products of hydrolysis of a thioester?

A

A carboxylate and a thiol

63
Q

Is Catabolism oxidative or reductive?

A

Oxidative

64
Q

Is anbolism oxidative or reductive?

A

Reductive

65
Q

What happens to metabolites in catabolism?

A

They lose electrons (are oxidized)

66
Q

What happens to cofactors in catabolism?

A

They are reduced (this is why they are oxidizing agents)

67
Q

What happens to metabolites in anabolism?

A

They are reduced (gain electrons)

68
Q

What happens to cofactors in anabolism?

A

They are oxidized (this is why they are called reducing agents)

Biocheem (38 decks)

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