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Z OLD Molecules, Genes and Disease > Enzyme Activity > Flashcards

Enzyme Activity Flashcards

1
Q

Give the general equation for a reversible reaction

A

Substrate ↔ products

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2
Q

What must be true if a reaction is going to occur?

A

There must be a change in energy

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3
Q

Why must there be a change in energy for a reaction to occur?

A

Because of the making and breaking of bonds

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4
Q

What is important for overcoming energy barriers?

A

Enzymes

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5
Q

Why are enzymes important for overcoming energy barriers?

A

They produce transition states

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6
Q

What is the transition state?

A

The high energy intermediate that lies between substrate and products

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7
Q

What is the activation energy?

A

The minimum energy that substrate must have to allow for the reaction

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8
Q

What must be done to increase the rate of reaction?

A

The energy barrier must be overcome

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9
Q

How can the rate of reaction be increased?

A
  • Temperature
  • Concentration
  • Enzymes
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10
Q

How does temperature increase rate of reaction?

A

It increases the number of molecules with the activation energy

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11
Q

How does concentration increase in the rate of reaction?

A

It increases the chance of molecular conditions

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12
Q

What are the limitations of changing the rate of reaction using temperature and concentration?

A

They can’t really be changed in biological systems

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13
Q

What are enzymes?

A

Biological catalysts that increase the rate of reaction by lowering the activation energy

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14
Q

What do enzymes facilitate?

A

The formation of the transition state

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15
Q

Why is rate of reaction important?

A

Because some reactions are very slow, so even if it’s a favourable reaction, it may not occur

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16
Q

What are the features of enzymes?

A
  • Highly specific

- Unchanged after reaction

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17
Q

What is the result of enzymes being highly specific?

A

They normally only work for 1 or 2 reactions

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18
Q

Do enzymes change at all?

A

They may be changed during the reaction

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19
Q

What do enzymes do to rate of reaction?

A

Increase it

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20
Q

What kind of molecules are enzymes?

A

Proteins (with one or two exceptions)

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21
Q

What may enzymes require?

A

Associated cofactors

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22
Q

What are cofactors?

A

Other things that allow enzymes to work

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23
Q

Why are enzymes relevant in medicine?

A
  • Inheritable genetic disorders can be caused by changes in an enzyme
  • Overactive enzymes can cause disease
  • Measurement of enzyme activity for diagnosis
  • Inhibition of enzymes for drugs
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24
Q

How can genetic disorders cause problems with enzymes?

A

Mutations can destroy or slow an enzyme

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25
Q

Give an example of a disease caused by an overactive enzyme?

A

Some cancers

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26
Q

What is the active site?

A

The place where substrates bind, and where chemical reactions occur

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27
Q

How much of the enzyme does the active site occupy?

A

Only a small part; 5-6 amino acids

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28
Q

What is the purpose of the rest of the enzyme?

A

Acts as a scaffold for the active sit

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29
Q

What is the active site formed from?

A

Amino acids from different parts of the primary sequence

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30
Q

How is it possible that the active site amino acids come from different parts of the amino acid sequence?

A

When the protein is in it’s 3D confirmation, the amino acids are bought close together

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31
Q

Where do amino acids usually sit?

A

In clefts or crevices- not usually on the surface

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32
Q

What does the creft/crevice in which the active site usually do?

A

Excludes water

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33
Q

Why does the cleft/crevice the active site sits in usually exclude water?

A

Because water is so concentrated that it can interfere with the reaction

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34
Q

What shape is the active site?

A

One that is complementary to the substrate

35
Q

What does the binding of the substrate to the active site induce?

A

A change in confirmation

36
Q

What is the theory that the binding of substrate to the active site causes a change in confirmation called?

A

The induced fit hypothesis

37
Q

When does the active site form a completely complementary shape to the substrate?

A

After the substrate has binds

38
Q

What happens as the substrate binds?

A

The enzyme changes shape to accommodate the substrate

39
Q

How is the substrate bound to the active site?

A

By multiple weak bonds

40
Q

What type of bonds bind the active site to the substrate?

A

All non-covalent

41
Q

Why must the binding of active site to substrate not be too tight?

A

Otherwise the product would not be released

42
Q

What is the importance of the non-covalent interactions binding the substrate to the active site?

A

They hold it in exactly the right conformation

43
Q

How do enzymes work?

A

By stabilising the transition state

44
Q

What happens as the substrate levels decrease?

A

Product levels increase

45
Q

What is V 0 ?

A

The initial rate of reaction

46
Q

Why do we use V 0 ?

A

Because when measuring rate of reaction, we must know the concentration of the substrate, and the only time we know this is right at the start

47
Q

What do different enzymes have?

A

Different optimum conditions

48
Q

What do optimum conditions consist of?

A

NAME?

49
Q

What often happens as an enzyme catalysed reaction reaches maximum velocity?

A

The plot of reaction rate as a function of substrate concentration has the shape of a rectangular hyperbola

50
Q

What does the Michaelis-Menten model for enzyme catalysis propose?

A

That a specific complex between enzyme and substrate is a necessary intermediate in catalysis

51
Q

Give the chemical equation for the Michaelis-Menten model

A

E+S ↔ ES → E+P

52
Q

What is the Michaelis-Menten equation?

A

V 0 = Vmax[S] / Km + [S]

Where Km = Michaelis constant
and V max = maximal velocity (mol/min)
Assuming an infinite [substrate]

53
Q

What does the Michaelis-Menten equation predict?

A

A plot of V 0 versus [S] will be a rectangular hyperbola

54
Q

What does the Michaelis-Menten equation tell us?

A

That rate is dependent on concentration

55
Q

Do all enzymes obey the Michaelis-Menten model?

A

No

56
Q

Which enzymes often don’t follow the Michaelis-Menten model?

A

Regulated enzymes that show co-operativity

57
Q

What is Vmax?

A

The maximal rate when all enzymes active site are saturated with substrate

58
Q

What does Vmax vary depending on?

A

Concentration of enzyme being measured

59
Q

What is Km?

A

Substrate concentration that gives half maximal velocity

60
Q

What do Km values give?

A

A measure of affinity of an enzyme to its substrate

61
Q

What does a low Km mean?

A

High affinity for substrate

62
Q

What does a high Km mean?

A

Low affinity for substrate

63
Q

What is 1 unit?

A

The amount of enzyme that can catalyse 1 micromole of product per minute

64
Q

What is the Lineweaver-Burk plot?

A

1/V 0 = Km/Vmax . 1/[S] + 1/Vmax

65
Q

How can Km be determined from the Lineweaver-Burk plot?

A

It is the negative reciprocal of where the plot meets the x-axis

66
Q

How can Vmax be determined from the Lineweaver-Burk plot?

A

It is the reciprocal of where the plot meets the y axis

67
Q

What are enzyme inhibitors?

A

Molecules that slow down or prevent enzyme reactions

68
Q

What do enzyme inhibitors include?

A

Many drugs

69
Q

Are enzyme inhibitors reversible or irreversible?

A

Can be either

70
Q

What happens when enzyme inhibitors are irreversible?

A

They bind very tightly, generally using a form of covalent bond, blocking function completely

71
Q

What happens when enzyme inhibitors are irreversible?

A

They bind non-covalently and can free dissociate

72
Q

What are the two types of enzyme inhibition?

A

NAME?

73
Q

Where do competitive inhibitors bind?

A

Active site

74
Q

What must be true of a competitive inhibitor?

A

It must also be complementary to the active site

75
Q

What does a competitive inhibitor reduce?

A

The proportion of enzyme molecules bound to substrate

76
Q

Does a competitive inhibitor affect Km or Vmax?

A

Km

77
Q

Why does a competitive inhibitor not affect Vmax?

A

Adding enough substrate will always overcome the effect of the inhibitor

78
Q

Why does a competitive inhibitor increase Km?

A

Because the inhibitor competes with the substrate for active sites

79
Q

Where does a non-competive inhibitor bind?

A

Another site of the enzyme

80
Q

Does a non-competitive inhibitor affect Km or Vmax?

A

Vmax

81
Q

What does a non-competitive inhibitor decrease?

A

The turnover number of an enzyme

82
Q

How does a non-competive inhibitor exert its effect?

A

It changes the overall shape of the molecule

83
Q

What other affect can compounds binding outside the active site have?

A

They can activate the enzyme, rather than inhibit

Z OLD Molecules, Genes and Disease (14 decks)

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