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Science for Medicine > Enzymes 1 > Flashcards

Enzymes 1 Flashcards

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1
Q

What are virtually all reactions in the body mediated by?

A

Enzymes

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2
Q

What is an enzyme?

A

A biological catalyst that increases the rate of a reaction without being changed in the overall process

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3
Q

How are enzymes efficient?

A

They catalyse at a very high reaction rate

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4
Q
A
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5
Q

What is meant by the specificity of enzymes?

A

They are very specific, with only certain substrates binding to them

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6
Q

Are can enzyme reactions be controlled?

A

They can be regulated

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7
Q

What pH and temperature conditions do enzymes work in?

A

Mild

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8
Q

How do the set of enzymes in a cell determine which metabolic pathways take place?

A

They are so specific

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9
Q

What are ribozymes?

A

Catalytic RNA molecules with no protein content

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10
Q

What are enzymes named and classified according to?

A

The reactions that they catalyse

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11
Q

What is a cofactor?

A

Non protein component needed for activity

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12
Q

What is usually the cofactor?

A

An ion such as Fe2+, Fe3+, K+ or Mg2+

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13
Q

What is a coenzyme?

A

Complex organic molecule that is usually produced from vitamins

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14
Q

Give some examples of coenzymes?

A

FAD (comes from riboflavin)

NAD (comes from niacin)

Coenzyme A (comes from pantothenate)

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15
Q

What is a prosthetic group?

A

Cofactor covalently bound to an enzyme or very tight associated with the enzyme

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16
Q

What is an example of a prosthetic group?

A

The haem in haemoglobin

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17
Q

What is an apoenzyme?`

A

Protein component of an enzyme that contains a cofactor

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18
Q

What is a haloenzyme?

A

‘Whole enzyme’, the apoenzyme plus the cofactor

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19
Q

What is a substrate?

A

Molecules acted on by an enzyme

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20
Q

What is the active site?

A

Part of an enzyme in which the substrate bind and is acted upon

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21
Q

What does the name of an enzyme normally end in?

A

-ase, the name also normally relates to the function

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22
Q

What are the 6 classes of enzymes?

A

Oxidoreductases

Transferases

Hydrolases

Lyases

Isomerases

Ligases

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23
Q

What do oxidoreductases do?

A

Transfer electrons

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24
Q

What do transferases do?

A

Transfer groups

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25
Q

What do hydrolases do?

A

Hydrolyse (transfer chemical groups to water)

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26
Q

What do lyases do?

A

Form or add groups to double bonds

27
Q

What do isomerases do?

A

Transfer groups within molecules (form isomers)

28
Q

What do ligases do?

A

Formation of C-C, C-S, C-O and C-N (coupled to ATP cleavage)

29
Q

What are two things that enzymes do not do to a reaction?

A

Move the reaction equilbrium

Make a non spontaneous reaction spontaneous

30
Q

What are 3 things that enzymes do?

A

Increase the rate of a spontaneous reaction

Lower the activation energy of biochemical reactions

Accerlerate movement towards equilbrium

31
Q

What delta G value must spontaneous reactions have?

A

Negative so they will increase entropy

32
Q

When does the transition state occur?

A

When the stable molecules become unstable and may carry on to the product or revert back to the substrate

33
Q

Why are spontaneous reacitons not instantaneous?

A

Because of the energy barrier

34
Q

What is the energy barrier?

A

Energy required to position chemical groups correctly, bond rearrangments, e- rearrangement etc

35
Q

What does an enzyme allow a reaction to occur through?

A

A different route

E+S ⇔ ES ⇔ EP ⇔ E + P

36
Q

What does induced fit mean?

A

Conformation changes in protein structure when the substrate binds

37
Q

What are 3 techniques used to analyse an enzymes?

A

Mutagenesis

3D structure

Enzyme kinetics

38
Q

What would happen to the initial rate of a reaction if we changed the substrate concentration?

A

The initial rate of the ration would also change

39
Q

Why does the rate of the reaction decrease as time proceeds?

A

The substrate is used up

40
Q

How can the initial velocity (vo) be studied?

A

By knowing the precise [S], and having lots of S

41
Q

What does a graph of substrate concentration against vo look like?

A
42
Q

What happens to vo as initial [S] increases?

A

It increases until it levels out due to all of the enzymes active sites being used

43
Q

Why at higher [S] does vo change very little?

A

Due to the finite number of enzymes

44
Q

What is vmax?

A

Occurs when [S] becomes so large that vo changes a vanishably small amount (all enzyme active sites are saturated with substrate)

45
Q

When does vmax occur?

A

When all enzyme sites are saturated with substrate

46
Q

What is the model that Machaelis and Menten proposed to acount for the curve of [S] against vo?

A
  1. First part of the reaction occurs reversible
  2. Second part occurs more slowly
47
Q

What limits the rate of the entire reaction?

A

The second step (ES to E + P) is the slowest step and so is the rate determining step

48
Q

What is the rate of the reaction proportional to?

A

Amount of ES

49
Q

What is the M-M equation?

A
50
Q

What is KM (Michaelis constant)?

A

Substrate concentration at half of the vmax

51
Q

Whats happens to the M-M equation when [S] is equal to KM?

A

It looks like Vo = Vmax/2

52
Q

What is the steady state assumption?

A

[ES] does not change with time due to the rate of formation being equal to the rate of breakdown

53
Q

Why is it hard to determin vmax using the graph of [S] against vo?

A

The graph curves and basically goes to infiity

54
Q

What is the most accurate way to determine vmax experimentally?

A

Drawing a Lineumer-Burk plot (double reciprical plot)

55
Q

That does the intersection of the y-axis on a Lineurner-Burk plot represent?

A

1/vmax

56
Q

What does the intersection of the x-axis on a Lineumer-Burke plot represent?

A

1/KM

57
Q

What can KM also be defined as?

A

KM = (K-1 + K2) / K1

Because K2 is the rate limiting step (K2 < K-1):

KM = K-1 / K1

58
Q

What can KM also be termed as?

A

The dissociation constant of the ES complex

59
Q

What can KM be described as it terms of rate?

A

Ratio of rate constant for break of ES to E+S compared to the ratio contant for formation of ES from E+S

60
Q

What does KM indicate about an enzyme and a substrate?

A

The affinity of the enzyme with that substrate

61
Q

What does a large KM mean?

A

Less stable ES complex (low affinity)

62
Q

What does a low KM mean?

A

More stable ES complex (high affinity)

63
Q

What does vmax tell you?

A

How fast the reaction is proceeding when the enzyme is saturated with substrate

64
Q

What do KM and vmax change in response to?

A

The cells condition, the same enzyme may function differently in different cells

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