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A Level Biology > 2.4 Enzymes > Flashcards

2.4 Enzymes Flashcards

1
Q

What are enzymes

A

Biological catalysts

‘Biological’ because they function in living systems
‘Catalysts’ because they speed up the rate of chemical reactions without being used up or undergoing permanent change

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2
Q

What type of proteins are enzymes

A

globular proteins with complex tertiary structures

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3
Q

What do enzymes control

A

Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
Virtually every metabolic reaction within living organisms is catalysed by an enzyme
Enzymes are therefore essential for life to exist

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4
Q

How process produces enzymes

A

Protein synthesis inside cells

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5
Q

Intracellular enzymes

A

Are produced and function inside the cell

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6
Q

Extracellular enzymes

A

Secreted by cells ad catalyse reactions outside cells

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7
Q

Catalase

A

Intracellular enzymes
Converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues

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8
Q

Amylase

A

Extra cellular enzyme
Hydrolyses starch into simple sugars

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9
Q

What secrets amylase

A

Salivary glands and the pnancreas

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10
Q

Where is starch digested

A

The mount and small intestine

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11
Q

Trypsin

A

Extracellular digestive enzyme
Breaks down proteins into peptides and amino acids

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12
Q

What secretes trypsin

A

Pancreas and small intestine

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13
Q

Active site

A

where specific substrates bind forming an enzyme-substrate complex

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14
Q

What can change the shape of the active site

A

Heat or pH

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15
Q

Desaturation

A

Extremes of heat or pH can change the shape of the active site, preventing substrate binding

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16
Q

What must happen in order for reaction to occur

A

Substrates collide with enzymes active site and this must happen at correct orientation and speed

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17
Q

Enzymes specificity

A

The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)

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18
Q

What is the shape of the active site determined by

A

complex tertiary structure of the protein that makes up the enzyme:

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19
Q

How does structure of proteins determine shape of active site

A

Proteins are formed from chains of amino acids held together by peptide bonds
The order of amino acids determines the shape of an enzyme
If the order is altered, the resulting three-dimensional shape changes

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20
Q

Enzyme-substrate complex

A

An enzyme-substrate complex forms when an enzyme and its substrate join together

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21
Q

How long is the enzyme-substrate complex formed for

A

only formed temporarily before the enzyme catalyses the reaction and the product(s) are released

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22
Q

Lock and key hypothesis

A

that both enzymes and substrates were rigid structures that locked into each other very precisely

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23
Q

Induced-fit hypothesis

A

The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme

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24
Q

Conformational changes

A

The slight change in shape in order for enzyme-substrate complex to be made

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25
Q

What does conformational change ensure

A

an ideal binding arrangement between the enzyme and substrate is achieved

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26
Q

Why does conformational changes happen

A

To maximise the ability of the enzyme to catalyse the reaction

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27
Q

Activation energy

A

the amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed

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28
Q

How do enzymes affect activation energy

A

Enzymes speed up chemical reactions because they reduce the stability of bonds in the reactants

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29
Q

What does the destabilisation of bonds lead to

A

Makes it more reactive

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30
Q

What would happen if without enzymes

A

extremely high temperatures or pressures would be needed to reach the activation energy for many biological reactions

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31
Q

Optimum pH

A

PH where enzymes operate best

32
Q

What happens to enzymes at extremes pH

A

Hydrogen and ionic bonds that hold the tertiary structure are broken which alters the shape of the active site causing denaturation

33
Q

Pepsin optimum pH

A

2

34
Q

Buffer solutions

A

Maintain specific pH

35
Q

Effect of pH practical

A

Iodine added to spotting tile
Add amylase + buffer solution mix and add starch solution
Start stopwatch
After 10 seconds add a drop of solution to spotting tile
Repeat every 10 seconds
Repeat steps using buffer solutions of different pH

36
Q

What should be kept the same in pH practical

A

Equal volume and concentration of enzyme

37
Q

How could you improve ph practical

A

Control temperature by using water bath at 35 degrees

38
Q

Enzymes optimum temperature

A

Temperature at which they catalyse a reaction at the maximum rate

39
Q

How do lower temperatures affect reaction

A

prevent reactions from proceeding or slow them down

40
Q

Why do lower temperatures affect enzymes activity

A

Molecules move relatively slowly as they have less kinetic energy

Less kinetic energy results in a lower frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to less frequent enzyme-substrate complex formation

Substrates and enzymes also collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)

41
Q

How do higher temperatures affect enzyme activity

A

Speed up reactions

42
Q

Why do higher temperatures affect enzyme activity

A

Molecules move more quickly as they have more kinetic energy
Increased kinetic energy results

in a higher frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to more frequent enzyme-substrate complex formation

Substrates and enzymes also collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)

43
Q

How does temperature affect enzyme activity if its too high

A

the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature

44
Q

Why does extreme temperatures cause denaturation

A

Increased kinetic energy and vibration puts strain on enzyme molecules causing weaker hydrogen and ionic bonds to start to break
Breaking of bonds cause tertiary structure to change
Active site permanently damaged and its shape is no longer complementary to the substrate preventing the substrate from binding

45
Q

Temperature coefficient

A

the ratio between the rates of that reaction at two different temperatures

46
Q

Temperature coefficient equation

A

Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)

47
Q

What does a higher enzyme concentration mean

A

The higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation

48
Q

How does enzyme concentration affect rate of reaction

A

As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration
If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting facto

49
Q

what does a higher substrate concentration mean

A

The greater the substrate concentration, the higher the rate of reaction

50
Q

Why does a higher substrate concentration increase rate of reaction

A

As the number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases

51
Q

How does increased substrate concentration affect rate of reaction

A

Increases however If the enzyme concentration remains fixed but the amount of substrate is increased past a certain point, however, all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate
When the active sites of the enzymes are all full, any substrate molecules that are added have nowhere to bind in order to form an enzyme-substrate complex

52
Q

Reversible inhibitor

A

can reduced or stop enzyme activity temporarily

53
Q

Two types of reverse inhibitors

A

Competitive and non-competitive

54
Q

Competitive inhibitor

A

have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site

55
Q

Non-competitive inhibitor

A

bind to the enzyme at an alternative site, which alters the shape of the active site and therefore prevents the substrate from binding to it

56
Q

What happens if you increase concentration of an inhibitor

A

reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely

57
Q

What happens if you increase the substance concentration to counter the competitive inhibitor

A

increasing the substrate concentration can increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes)

58
Q

What happens if you increase the substance concentration to counter non-competitive inhibitors

A

increasing the substrate concentration cannot increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form

59
Q

What can reversible inhibitors act as

A

regulators in metabolic pathways

60
Q

End-product inhibition

A

End-product of reaction binds to alternative site on enzymes preventing esc’s being formed
The end product can then detach allowing active site to reform

61
Q

Non-reversible inhibitors

A

form covalent bonds with enzymes, inhibiting them permanently

62
Q

Why are non-reversible inhibitors dangerous

A

can cause the biological reaction the enzyme is catalysing to be completely stopped

63
Q

What is the only way to avoid biological reaction the enzyme is catalysing to be stopped by non-reversible inhibitors

A

produce more of the enzyme being inhibited, which can only be achieved by transcribing and translating the gene(s) for that enzyme, which is a relatively slow process

64
Q

Cofactors

A

Non-protein substance that changes enzymes tertiary structure which allows enzyme to function properly

65
Q

Cofactor for amylase

A

Chloride ions

66
Q

inorganic cofactor

A

Particular inorganic ions may help to stabilise the structure of the enzyme or may actually take part in the reaction at the active site

67
Q

Coenzymes

A

Organic non-protein cofactors

68
Q

What do coenzymes do

A

link different enzyme-catalysed reactions into a sequence during metabolic processes, such as photosynthesis and respiration

69
Q

An example of a source of coenzymes

A

Vitamins

70
Q

Prosthetic groups

A

Cofactors that are a permanent part of the structure of the enzymes they assist

71
Q

Why are profactors essential to enzymes functioning properly

A

they help to form the final 3D shape of the enzyme

72
Q

How can enzyme catalysed reactions be investigated

A

Measuring the rate of formation of a product
Measuring the rate of disappearance of a substrate

73
Q

Rate of product formation investigation

A

Catalase is an enzyme found in the cells of most organisms that breaks down hydrogen peroxide into water and oxygen
Hydrogen peroxide and catalase are combined and the volume of oxygen generated is measured in a set time
The rate of reaction can then be calculated

74
Q

Investigating amylase activity using iodine
Rate of substrate disappearance

A

Amylase and starch are combined and this reaction mixture is then tested for starch at regular time intervals
This can be done by taking samples from the reaction mixture at each time interval and adding each sample to some iodine in potassium iodide solution
Starch forms a blue-black colour with this solution
If no starch is present, the iodine solution remains yellow-brown
In this way, the time t

75
Q

Amylase

A

digestive enzyme that hydrolyses starch into maltose and glucose

A Level Biology (10 decks)

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