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OCR A level biology > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is the Vmax?

A

Maximum initial velocity or rate of an enzyme-catalysed reaction

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2
Q

What kind of proteins are enzymes?

A

Globular

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3
Q

What is an enzyme?

A

A protein that acts as a catalyst in biological reactions

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4
Q

What is the relationship between the shape of the active site and the shape of the substrate?

A

They have complementary shapes

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5
Q

Give an example of an intracellular enzyme

A

Catalase

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6
Q

Give an example of an extracellular enzyme

A

Amylase

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7
Q

Define metabolic reactions

A

The reactions occurring inside the bodu at any given time

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8
Q

Where are enzymes produced?

A

On the ribosomes of a cell

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9
Q

How do enzymes speed up the rate of reaction?

A

They reduce the activation energy of a reaction

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10
Q

What are the two models for enzyme action?

A

The lock and key
and
The induced fit

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11
Q

Describe the lock and key model of enzyme action

A

The enzyme is the lock and the substrate is the key
The correct key must be used to fit in the correct lock
Only a key that fits exactly into the lock will work

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12
Q

What does the lock and key model of enzyme action suggest about the active site?

A

The active site is ridgid

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13
Q

Describe the induced fit model of enzyme action

A
  • The substrate and active site are complementary in shape but not an exact fit
  • the active site is able to change shape slightly to create a perfect fit
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14
Q

What does the induced fit model suggest about the active site?

A

The active site has a degree of flexibility

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15
Q

Outline how an enzyme causes a reaction to occur

A
  • the substrate and active site collide, forming an enzyme-substrate complex
  • the active site puts pressure on the bonds of the substrate
  • this causes them to break, forming an enzyme-product complex
  • the products are released and the enzyme reused
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16
Q

How do enzymes reduce the activation energy of a reaction?

A
  • They put pressure on the bonds in a substrate

- They bring atom groups close enough to react

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17
Q

Define metabolic pathway

A

A series of enzyme reactions whereby the product becomes the substrate of the next

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18
Q

What are anabolic reactions?

A

Reactions that build molecules

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19
Q

What are catabolic reactions?

A

Reactions that break bonds/break up molecules

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20
Q

How do R-groups of the enzyme help to break apart substrates?

A

The R-groups interact with the substrate, forming temporary bonds with the substrate which puts pressure on the bonds in the substrate bonds

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21
Q

Outline how starch is broken down in the body

A
  • starch polymers are partially broken down into maltose by amylase
  • amylase is released into the mouth via the salivary glands
  • amylase is released into the small intestine via the pancreas
  • maltose is then broken down into glucose by maltase in the small intestine
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22
Q

Outline how protein is broken down in the body

A
  • trypsin is produced by the pancreas
  • trypsin breaks proteins into smaller peptides in the small intestine

-other proteases then break the small peptides into amino acids

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23
Q

What is the active site?

A

the area of an enzyme with a shape complementary to a specific substrate allowing the enzyme to bind to a substrate with specicifity

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24
Q

Why are enzymes important to life?

A
  • life processes require chemical reactions
  • the reactions need to happen quickly
  • enzymes allow these reactions to occur quickly without high pressure/temperature
  • allow organisms to get the nutrients needed to function i.e through digestion
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25
Q

What is activation energy?

A

The energy required for a reaction to start

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26
Q

What is the substrate of catalase?

A

Hydrogen peroxide

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27
Q

What are the products of the reaction of catalase?

A

2H2O and O2

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28
Q

What is the substrate of amylase?

A

Starch

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29
Q

What are the products of the reaction of amylase?

A

Maltose

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30
Q

What is the substrate of trypsin?

A

Protein

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31
Q

What are the products of the reaction of trypsin?

A

polypeptides

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32
Q

How are metabolic pathways controlled?

A
  • By allosteric enzymes whereby the end product of the pathway binds to the allosteric site
  • once the end product levels fall, the inhibition is lifted
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33
Q

Give an example of control of a metabolic pathway

A

In respiration the enzyme PFK is inhibited by ATP and activated by ADP

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34
Q

What is the approximate optimum temperature for most enzymes in the human body?

A

40 degrees

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35
Q

What happens to the rate of reaction during the exponential phase?

A

-rate of reaction doubles every time temperature increases by 10 degrees

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36
Q

Why does the rate of reaction increase up to 60 degrees, as temperature increases?

A
  • as temperature increases, kinetic energy of particles increases
  • this means particles move faster and collide more frequently
  • increasing rate of reaction
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37
Q

Why does the rate of reaction decrease beyond 60 degrees?

A
  • hydrogen bonds and ionic bonds break
  • loss of tertiary structure
  • change in shape of the active site
  • substrate no longer fits
  • decreasing rate of reaction
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38
Q

Across how many pH units do enzymes work across?

A

4

39
Q

Describe the rate of reaction graph for pH

A
  • symmetrical curve
  • optimum pH
  • range of pH, 2 pH units either side of optimum
  • rate of reaction falls to 0 beyond pH range
40
Q

What is lost in denaturation?

A

tertiary structure/ shape of active site

41
Q

What occurs in denaturation?

A
  • active site changes shapes
  • shape no longer complementary to the substrate
  • substrate can no longer fit into the active site
  • enzyme no longer acts as a catalyst
42
Q

How does an increase in substrate concentration increase rate of reaction?

A
  • higher chance of collisions
  • limited by enzyme concentration
  • higher chance of successful collisions
  • more substrate-enzyme complexes can be formed
43
Q

Is the change in shape of active site due to pH reversible?

A

Yes

44
Q

Which 5 factors affect rate of enzyme controlled reaction?

A
  • temperature
  • pH
  • substrate concentration
  • enzyme concentration
  • enzyme inhibitors
45
Q

What are the two main types of inhibitors?

A
  • competitive

- non-competitive

46
Q

What is the effect of an increase in enzyme concentration on the rate of reaction?

A
  • it increases the rate of reaction

- up to a point where rate of reaction is limited by substrate concentration

47
Q

Why does an increase in enzyme concentration increase rate of reaction?

A
  • there are more active sites
  • higher chance of a successful collision
  • to form an enzyme-substrate complex
48
Q

How do competitive inhibitors reduce rate of reaction?

A
  • compete with the substrate for the active site

- sit in the active site and block the substrate from entering the active site

49
Q

What is the relationship between the shape of the inhibitor for a particular reaction and it’s substrate?

A

They have SIMILAR shapes

50
Q

Are competitive inhibitors reversible?

A

Yes

51
Q

Why are competitive inhibitors reversible?

A

They do not cause the enzyme to lose its shape

52
Q

What is the degree of inhibition caused by competitive inhibitors dependent on?

A

The relative concentrations of substrate and inhibitor

53
Q

What is the effect of a greater concentration of a competitive inhibitor on the rate of reaction?

A

It decreases the rate of reaction

54
Q

Why does a greater concentration of a competitive inhibitor decrease the rate of reaction?

A
  • a greater concentration of inhibitor relative to substrate means:
  • the probability of a collision between an enzyme and an inhibitor is greater than the probability of a collision between an enzyme and a substrate
55
Q

Give a difference between competitive and non-competitive inhibitors

A

-non-competitive do not compete with the substrate for the active site whilst competitive do
or
-non-competitive inhibitors bind to allosteric site whilst competitive do not

56
Q

What are the two types of non-competitive inhibitor?

A
  • reversible

- irreversible

57
Q

Give an example of a reversible non-competitive inhibitor

A

Metabolic poisons, such as cynanide

58
Q

How does cyanide act as a poison?

A
  • acts on cytochromeoxidase (an enzyme involved in respiration)
  • inhibits respiration
  • no ATP therefore is produced so death occurs
59
Q

What reaction is cytochromeoxidase involved in?

A

Aerobic respiration

60
Q

How does the antidote to cyanide work?

A

It has a higher affinity for cyanide than cytochromeoxidase

61
Q

How do non-competitive inhibitors inhibit the action of enzymes?

A

-they bind to the allosteric site

causing the active site to change shape so the substrate no longer fits

62
Q

Give an example of an irreversible non-competitive inhibitor

A

Heavy metals, such as mercury

63
Q

How does mercury act as an irreversible non-competitive inhibitor?

A
  • breaks covalent bonds in the enzyme
  • loss of tertiary and quaternary structures
  • loss of shape of active site
  • substrate can no longer fit so the enzyme loses its function
64
Q

Which enzyme does cyanide act on?

A

Cytochromeoxidase

65
Q

Define cofactors

A

non-protein components required for the effective functioning of an enzyme

66
Q

What are the 3 types of cofactors?

A
  • inorganic ion cofactors
  • coenzymes
  • prosthetic groups
67
Q

What are coenzymes?

A

Organic molecules, mostly derived from B vitamins, which bind temporarily to an enzyme

68
Q

Give an example of a coenzyme

A

NAD

69
Q

What is NAD synthesised from?

A

Vitamin B3

70
Q

What process is NAD used in?

A

Aerobic respiration

71
Q

Which reaction of aerobic respiration does NAD take part in?

A

The reaction of pyruvate to Acetyl Coenzyme A

link reaction

72
Q

What is the function of NAD?

A

Used to transfer hydrogen atoms between molecules

73
Q

What happens to NAD during the reaction of pyruvate to acetyl coenzyme A?

A

It is reduced

74
Q

What is coenzyme A used for?

A

Breakdown of fatty acids and carbohydrates (in respiration)

75
Q

What process is conezyme A used in?

A

Aerobic respiration

76
Q

Do cofactors bind temporarily or permanently to an enzyme?

A

Temporarily

77
Q

Define inorganic ion cofactor

A

Inorganic ions obtained from the diet which bind temporarily to the enzyme

78
Q

Give an example of an inorganic cofactor

A

Cl- ion for amylase

79
Q

How does Cl- act as a cofactor for amylase?

A

Temporarily binds with amylase active site
Modifies the active site shape
Allowing the starch (substrate) to fit into the active site and the enzyme to work

80
Q

Which enzyme requires a zinc ion as a prosthetic group?

A

Carbonic anhydrase

81
Q

Define prosthetic group

A

Organic or metal ions which bind permanently to the enzyme

82
Q

What is the function of carbonic anhydrase?

A

Enables CO2 to be quickly dissolved in the blood for transporation

83
Q

What is a precursor/apo enzyme?

A

An inactive form of a particular enzyme

84
Q

Which enzyme is a chloride ion an essential cofactor for?

A

Amylase

85
Q

What is a zymogen/protoenzyme?

A

Enzymes which require part of their polypeptide to be removed to bring about a change in the shape of the active site/ to reveal the active site to activate the enzyme

86
Q

Give two factors which can activate a protoenzyme?

A
  • Protease

- Change in pH

87
Q

How does protease activate a protoenzyme?

A

removes part of the protoenzyme by cleaving certain bonds to reveal the active site

88
Q

How does a change in pH activate a protoenzyme?

A

Results in changes in the tertiary structure to reveal the active site

89
Q

What is the difference between a coenzyme and an ion cofactor?

A

A coenzyme is an organic molecule whereas ion cofactors are inorganic ions

90
Q

How can the effect of concentration of an enzyme be investigated experimentally?

A
  • serial dilutions of trypsin are made
  • milk powder is added to each
  • the time taken for text behind the test tube to become visible is recorded
91
Q

Give 2 examples of competitive inhibitors

A

Aspirin and statins

92
Q

Why might enzymes be produced in inactive forms?

A
  • the enzymes could otherwise damage cells/tissues

- the action of the enzymes needs to be controlled/only used under certain conditions

93
Q

Give 3 ways a precursor enzyme can be activated

A
  • change in pH
  • protease
  • cofactor added

OCR A level biology (44 decks)

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