Enzymes 1 Flashcards Preview

Science for Medicine > Enzymes 1 > Flashcards

Flashcards in Enzymes 1 Deck (64):
1

What are virtually all reactions in the body mediated by?

Enzymes

2

What is an enzyme?

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

3

How are enzymes efficient?

They catalyse at a very high reaction rate

4

5

What is meant by the specificity of enzymes?

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

6

Are can enzyme reactions be controlled?

They can be regulated

7

What pH and temperature conditions do enzymes work in?

Mild

8

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

They are so specific

9

What are ribozymes?

Catalytic RNA molecules with no protein content

10

What are enzymes named and classified according to?

The reactions that they catalyse

11

What is a cofactor?

Non protein component needed for activity

12

What is usually the cofactor?

An ion such as Fe2+, Fe3+, K+ or Mg2+

13

What is a coenzyme?

Complex organic molecule that is usually produced from vitamins

14

Give some examples of coenzymes?

FAD (comes from riboflavin)

NAD (comes from niacin)

Coenzyme A (comes from pantothenate)

15

What is a prosthetic group?

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

16

What is an example of a prosthetic group?

The haem in haemoglobin

17

What is an apoenzyme?`

Protein component of an enzyme that contains a cofactor

18

What is a haloenzyme?

'Whole enzyme', the apoenzyme plus the cofactor

19

What is a substrate?

Molecules acted on by an enzyme

20

What is the active site?

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

21

What does the name of an enzyme normally end in?

-ase, the name also normally relates to the function

22

What are the 6 classes of enzymes?

Oxidoreductases

Transferases

Hydrolases

Lyases

Isomerases

Ligases

23

What do oxidoreductases do?

Transfer electrons

24

What do transferases do?

Transfer groups

25

What do hydrolases do?

Hydrolyse (transfer chemical groups to water)

26

What do lyases do?

Form or add groups to double bonds

27

What do isomerases do?

Transfer groups within molecules (form isomers)

28

What do ligases do?

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

29

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

Move the reaction equilbrium

Make a non spontaneous reaction spontaneous

30

What are 3 things that enzymes do?

Increase the rate of a spontaneous reaction

Lower the activation energy of biochemical reactions

Accerlerate movement towards equilbrium

31

What delta G value must spontaneous reactions have?

Negative so they will increase entropy

32

When does the transition state occur? 

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

33

Why are spontaneous reacitons not instantaneous?

Because of the energy barrier

34

What is the energy barrier?

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

35

What does an enzyme allow a reaction to occur through?

A different route

E+S ⇔ ES ⇔ EP ⇔ E + P

36

What does induced fit mean?

Conformation changes in protein structure when the substrate binds

37

What are 3 techniques used to analyse an enzymes?

Mutagenesis

3D structure

Enzyme kinetics

38

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

The initial rate of the ration would also change

39

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

The substrate is used up

40

How can the initial velocity (vo) be studied?

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

41

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

42

What happens to vo as initial [S] increases?

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

43

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

Due to the finite number of enzymes

44

What is vmax?

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

45

When does vmax occur?

When all enzyme sites are saturated with substrate

46

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

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

47

What limits the rate of the entire reaction?

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

48

What is the rate of the reaction proportional to?

Amount of ES

49

What is the M-M equation?

50

What is KM (Michaelis constant)?

Substrate concentration at half of the vmax

51

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

It looks like Vo = Vmax/2

52

What is the steady state assumption?

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

53

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

The graph curves and basically goes to infiity

54

What is the most accurate way to determine vmax experimentally?

Drawing a Lineumer-Burk plot (double reciprical plot)

55

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

1/vmax

56

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

1/KM

57

What can KM also be defined as?

KM = (K-1 + K2) / K1

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

KM = K-1 / K1

58

What can KM also be termed as?

The dissociation constant of the ES complex

59

What can KM be described as it terms of rate?

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

60

What does KM indicate about an enzyme and a substrate?

The affinity of the enzyme with that substrate

61

What does a large KM mean?

Less stable ES complex (low affinity)

62

What does a low KM mean?

More stable ES complex (high affinity)

63

What does vmax tell you?

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

64

What do KM and vmax change in response to?

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