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Enzymes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are enzymes?

A

They are biological catalysts
They are proteins

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2
Q

What do enzymes do within a reaction?

A
  • They speed up the rate of reaction
  • They lower the activation energy by bending the bonds within the substrate
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3
Q

Are enzymes specific to one reaction?

A

Yes

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4
Q

Are enzymes used up or changed by the recation?

A

No

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5
Q

Do enzymes alter the product of the reaction?

A

No

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6
Q

Can they create reactions?

A

No - they only catalyse reactions which already occur

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7
Q

What kind of proteins are enzymes?

A

Globular

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8
Q

What do enzymes have that makes them strong?

A

They have a high molecular weight, they are substantial, solid and have a certain amount of stability
(so we try not to change the environment)

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9
Q

What are enzymes sensitive to?

A
  • Temperature and pH
  • They are denatured at high temperatures and at pH’s that they are not optimal in
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10
Q

Ho do high temperatures affect enzymes?

A

They are denatured as the bonds are broken - the active site changes shape

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11
Q

How do different pH’s affect enzymes?

A

They are denatured. Only hydrogen and ionic bonds in enzymes are affected by pH

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12
Q

What is the active site?

A

It is where the chemical reactions take place. It has a complimentary 3D tertiary structure to one specific substrate

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13
Q

What are the two types of reactions that enzymes catalyse?

A

Anabolic - building up
Catabolic - breaking down

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14
Q

What kind of reactions are digestion reactions?

A

Catabolic

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15
Q

Why are the majority of enzymes soluble in water?

A

Due to hydrophilic R variable groups on their amino acids

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16
Q

What is the reaction known as when an enzyme is inside the cell?

A

Intracellularly e.g. DNA replication happens inside cells

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17
Q

What is the reaction known as when an enzyme is outside the cell?

A

Extracellularly - it occurs outside of the cells which have constructed it e.g. in fluids
e.g. extracellular action of pepsin and amylase

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18
Q

What are the main groups of enzymes?

A

Oxidoreductase
Transferases
Lysases
Hydrolases
Ligases
Isomerases

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19
Q

What is oxidoreductase?

A

The transfer of electrons in oxidation and reduction reactions

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20
Q

What are transferases?

A

Transfer of a functional group from one molecule to another

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21
Q

What are lysases?

A

Splitting of bonds (not hydrolysis or oxidation)

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22
Q

What are hydrolases?

A

Hydrolysis of bonds (all digestive enzymes)

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23
Q

What are ligases?

A

Joining of 2 molecules by formation of covalent bonds

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24
Q

What are isomerases?

A

Isomerisation of molecules e.g. conversion of glucose and fructose to sucrose

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25
Q

What do some enzymes need before they catalyse a reaction?

A

Non-protein substances

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26
Q

What are activators?

A

Inorganic groups permanently bound to enzymes and are a type of prosthetic group e.g. iron, copper

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27
Q

What are co-enzymes?

A

Organic molecules that bind only temporarily to the enzyme, transferring a chemical group necessary required for the reaction

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28
Q

What is the lock and key model?

A
  • Substrate binds to active site
  • This creates an enzyme/substrate complex
  • Bends the bonds of the substrate
  • The reaction occurs and we have an enzyme/product complex
  • The active site releases products
  • The product molecules diffuse away from the active site
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29
Q

What does the lock and key model propose?

A

The substrate is an exact complimentary shape to the active site

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30
Q

What does the induced fit model take into account?

A

The fact that proteins (enzymes) have some 3 dimensional flexibility

31
Q

How does the induced fit model work?

A
  • Substrate binds to the enzyme at the active site which is a similar complimentary shape to the substrate but not exactly
  • Binding of the substrate induces the enzyme to change shape such that there is an exact fit in the active site once the substrate has bound
32
Q

According to the induced fit model, when can the reaction only take place?

A

After induced fit has occured

33
Q

What happens to the active site, according to the induced fit model, after the products are released?

A

It goes back to its original shape

34
Q

What is the activation energy?

A

The minimum amount of energy required for a reaction to start

35
Q

What affects the rate of enzyme catalysed reactions?

A
  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
  • Inhibitors
  • Activators
36
Q

At a low temperature, what is the rate of reaction like in enzymes?

A

Slow
Enzymes and substrates have little kinetic energy and move around less
So fewer successful collisions
Fewer enzyme/substrate complexes
We don’t achieve the activation energy
Less product per second being generated

37
Q

What happens as we increase the temperature up to the optimum to the rate of reaction in enzymes?

A

We increase kinetic energy
Increased number of successful collisions
Increased number of enzyme/substrate complexes
Increased rate of reaction
More product formed per second

38
Q

What happens as we increase the temperature by 10 degrees in enzyme controlled reactions?

A

The rate of reaction doubles
Q10 = 2

39
Q

What happens at the optimum temperature in enzyme controlled reactions?

A

Optimum is around 37 degrees
Fastest rate of reaction
Most successful collisions per second
Highest rate of enzyme/substrate complexes
Highest rate of product formation per second

40
Q

What happens at temperature above the optimum in enzyme controlled reactions?

A

The active site denatures
Its 3D tertiary structure is no longer complimentary to the substrate
There are fewer successful collisions per second
Lower rate of enzyme/substrate complexes forming
Lower rate of product formation per second
Decrease in rate of reaction

41
Q

What happens when the active site denatures?

A

The tertiary structure bonds are broken
This changes the 3D tertiary structure of the active site so no longer complimentary shape to the substrate

42
Q

Do specific enzymes all work over the same range of pH?

A

No- each one can only work over a particular range of pH

43
Q

Does each enzyme have its own optimum pH where the rate of reaction is maximum?

A

Yes

44
Q

What do changes in pH result in?

A
  • It affects the hydrogen and ionic bonds responsible for the tertiary structure shape of active sites
  • Extremes of pH break these bonds and denature the active sites
  • So it is no longer a 3D tertiary complimentary shape to the substrate
  • So fewer successful collisions per second
  • So fewer enzyme/ substrate complexes
  • So less product per second and rate of reaction drops
45
Q

If we have 10 active sites, until when is the substrate the limiting factor on rate of reaction?

A

Until there are 10 substrates

46
Q

When does the number of active sites become the limiting factor in the rate of reaction?

A
  • When the number of substrates exceeds the number of active sites
  • At this moment, all the active sites are occupied
  • The rate of reaction is at its fastest and an increase in substrate concentration does not increase the rate of reaction
  • There is a maximum number of enzyme substrate complexes
47
Q

Is rate of reaction directly proportional to enzyme concentration?

A

Yes - as enzyme concentration increases, the rate of reaction increases

48
Q

What happens when all the substrates are used up in a reaction?

A

The reaction is finished

49
Q

In living cells, what is the enzyme concentration like compared to the substrate concentration?

A

Enzyme concentrations are usually much lower than substrate concentration

50
Q

Is substrate concentration ever a limiting factor?

A

Rarely

51
Q

What is an inhibitor?

A

It is something that slows down the rate of reaction - inhibits the enzyme

52
Q

What is a competitive inhibitor?

A
  • It competes with the substrate to bind with the active site
  • It has a similar 3D shape to the substrate or a similar 3D complimentary shape to the active site
53
Q

What happens when a competitive inhibitor binds to the active site?

A

-It prevents enzyme/substrate complexes forming
- Active site is occupied so fewer products formed per second
- So lower rate of reaction

54
Q

What do inhibitors help us control?

A

The speed/rate of reaction of the enzyme

55
Q

Apart from the active site, are there any there binding sites on an enzyme?

A

Yes
There is a binding site/allosteric site away from the active site

56
Q

What kind of inhibitors bind to the binding site?

A

Non-competitive inhibitors as it does not bind to the active site

57
Q

What happens when a non-competitive inhibitor binds to the binding site?

A
  • It causes a 3D shape change to the active site so it is no longer a 3D complimentary shape to the substrate
  • It also prevents active site bending bonds
58
Q

How does a non-competitive inhibitor lower the rate of reaction?

A

It prevents successful enzyme/substrate complexes forming

59
Q

What happens if the non-competitive inhibitor is removed from the binding site?

A

The active site will return to its original 3D complimentary shape

60
Q

Are these types (competitive and non-competitive) of inhibitors reversible?

A

Yes and they can be removed

61
Q

When competitive inhibitors are present, what happens to the rate of reaction as substrate concentration is increased?

A
  • There is an increase in probability that the competitive inhibitor will not bind to the active site
  • So increasing number of enzyme/substrate complexes
  • Higher rate of reaction
62
Q

What can happen to the rate of reaction, with competitive inhibitors present, if we have a large enough substrate concentration?

A

They can out-compete the inhibitors and eventually reach the same rate of reaction as if there were no inhibitors

63
Q

What happens when there is a high substrate concentration but non-competitive inhibitors are present?

A
  • All enzyme active sites are occupied
  • But the substrate molecules bound to enzymes with attached inhibitors are not converted into product
  • So the maximum rates are never achieved
64
Q

If we have a large enough substrate concentration with non-competitive inhibitors present, can a maximum rate of reaction ever be achieved?

A
  • No
  • The effect of the inhibitor is not overcome by increasing the substrate concentration
  • Active sites do not convert substrate to product
  • The effect is equal to lowering enzyme concentration
65
Q

How do poisons act as inhibitors?

A

They are non-competitive inhibitors that bond to the binding site permanently

66
Q

What kind of reactions do poisons inhibit?

A

They stop metabolic reactions from occurring and essentially cause someone to die
(no energy from respiration so no energy for all reactions in the body etc)

67
Q

Apart from poisons, what can also act as inhibitors?

A

Drugs

68
Q

What is allosteric regulation?

A

The term used to describe any case in which a protein’s function at one site is affected by binding of a regulatory molecule at another site
(e.g non-competitive inhibitors or activators)

69
Q

What is end product inhibition important for?

A

Regulating metabolic pathways

70
Q

In end product inhibition, what does the end product often act as?

A

A regulator

71
Q

In end product inhibition, what happens when the end product concentration is high?

A

It binds non-competitively to an enzyme in the pathway, blocking further production of itself
(e.g. if there is an enzyme A in the beginning, it inhibits enzyme A)

72
Q

In end product inhibition, what happens when the product concentration begins to fall after the product has inhibited the reaction?

A

The product leaves the binding site and the active site is then available

73
Q

How is ATP synthesis regulated?

A

Through end product inhibition

Biology (12 decks)

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