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Enzymes Flashcards

1
Q

Define the term “enzyme”. (F)

A

A biological catalyst that interacts with substrate molecules to facilitate chemical reactions. Usually globular proteins.

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2
Q

Define the term “substrate”. (F)

A

A substance used, or acted on, by another process or substance i.e. a reactant.

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3
Q

Define the term “product”. (F)

A

The molecule(s) that is formed by a reaction.

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4
Q

Explain why enzymes are necessary to life.

A

Many processes necessary to life involve chemical reactions which need to happen very fast. Enzymes catalyse reactions without extreme conditions.

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5
Q

Define the term “anabolic reactions”.

A

Reactions of metabolism that construct molecules from smaller units, requiring energy.

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6
Q

Define the term “catabolic reactions”.

A

Reactions of metabolism that break molecules down into smaller units, releasing energy.

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7
Q

Define the term “digestion”.

A

The catabolic process in the digestive tract where ingested food is converted into simpler, soluble and diffusible substances that can be assimilated by the body.

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8
Q

Define the term “metabolism”.

A

The chemical processes that occur within a living organism in order to maintain life.

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9
Q

Define the term “intracellular enzyme”. Give one example.

A

An enzyme that acts inside the cell e.g. catalase.

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10
Q

Define the term “extracellular enzyme”. Give two examples.

A

An enzyme that acts outside the cell e.g. amylase, trypsin.

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11
Q

State the substrate for the enzyme catalase. (F)

A

Hydrogen peroxide (H2O2)

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12
Q

State the substrate for the enzyme amylase. (F)

A

Starch

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13
Q

State the substrate for the enzyme trypsin. (F)

A

Protein

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14
Q

State the products for the enzyme catalase. (F)

A

Oxygen and water

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15
Q

State the products for the enzyme amylase. (F)

A

Glucose

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16
Q

State the products for the enzyme trypsin. (F)

A

Polypeptides (amino acids by other enzymes)

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17
Q

Explain the role of extracellular enzymes in general.

A

Break down large nutrient molecules into smaller molecules that can enter cells to make products needed by the organism.

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18
Q

Summarise the digestion of starch as an example of the role of extracellular enzymes.

A
  • amylase in saliva and small intestine
  • partially breaks starch down into maltose
  • maltase in small intestine
  • breaks maltose into glucose
  • glucose absorbed into cells lining digestive system and bloodstream
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19
Q

Summarise the digestion of proteins as an example of the role of extracellular enzymes.

A
  • trypsin (protease) in small intestine
  • catalyses digestion of proteins into smaller peptides which can be broken down further into amino acids by other proteases
  • amino acids absorbed by cells lining digestive system and bloodstream
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20
Q

Define the term “active site”. (F)

A

The area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind to a substrate with specificity.

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21
Q

Define the term “complementary shape”. (F)

A

The shape of the active site and the substrate match so they can fit together.

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22
Q

Define the term “specific”. (F)

A

Each enzyme has a single substrate that it works on and that will fit into its active site.

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23
Q

Explain why an enzyme only catalyses one type of reaction. (F)

A

For an enzyme to work, the substrate has to be complementary to the active site of the enzyme. If it is not complementary, the reaction will not be catalysed.

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24
Q

State the sequence of events in an enzyme-controlled reaction. (F)

A
  • substrate fits into active site, forming the enzyme-substrate complex
  • lowers activation energy of reaction
  • reaction is catalysed and the enzyme-product complex formed
  • product is released from enzyme
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25
Q

Describe the “lock and key” hypothesis of enzyme action. (F) ***

A
  • only a specific substrate will fit into the active site of an enzyme
  • the active site is unchanging
  • the R-groups within the active site interact with the substrate
  • strain is put on the bonds within the substrate
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26
Q

Describe the “induced-fit” hypothesis of enzyme action. ***

A
  • active site of the enzyme changes shape slightly
  • changes in enzymes tertiary structure strengthen binding
  • puts strain on substrate molecule and weakens bonds
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27
Q

Suggest how the R-groups of amino acids are involved in catalysing reactions.

A

Interactions between R-groups in tertiary structure affect the shape of the active site and which substrates it can catalyse reactions for

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28
Q

Define the term “activation energy”. (F)

A

The energy required to initiate a reaction.

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29
Q

Define the term “rate of reaction”. (F)

A

How quickly the reaction takes place.

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30
Q

State what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.

A

Lowers the activation energy which means more molecules will have sufficient energy to initiate a reaction, so there are more successful collisions and a faster rate of reaction.

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31
Q

State 5 factors that affect the rate of an enzyme controlled reaction. (F)

A
  • enzyme concentration
  • substrate concentration
  • temperature
  • pH
  • inhibitors
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32
Q

Describe a graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time following the start of an experiment.

A
  • initially has steep gradient

- levels out to be flat

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33
Q

Explain the shape of a graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time.

A
  • initially the rate is steep because there is a high concentration of substrate
  • the gradient becomes less steep as the concentration of substrate decreases
  • the graph levels out when there is no more substrate to react
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34
Q

Explain the significance of the gradient of the line at any one point for the graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time.

A

The gradient is the rate of reaction.

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35
Q

Define the term “initial rate of reaction”.

A

The speed of the reaction at the start of the reaction (t=0)

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36
Q

Describe the significance of the initial rate of reaction in investigations into factors affecting the rate of enzyme-controlled reactions.

A

The initial rate of reaction is used to compare how the enzyme-controlled reactions differ when a factor is changed.

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37
Q

Describe a graph showing how temperature affects the initial rate of an enzyme-controlled reaction.

A
  • at low temperatures, the gradient is very shallow
  • slowly gets steeper as the temperature increases
  • peaks at the optimum temperature
  • gradient steeply decreases after optimum
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38
Q

Explain why increasing the temperature from below the optimum up towards the optimum increases the rate of reaction. (F)

A
  • react by colliding and forming the enzyme-substrate complex at the right energy
  • molecules have more kinetic energy
  • more likely to collide to form enzyme-substrate complex
  • more likely to have sufficient energy to form enzyme-substrate complex
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39
Q

Define the term “temperature coefficient, Q10”.

A

A measure of how much the rate of a reaction increases with a 10°C temperature increase.

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40
Q

State the temperature coefficient’s usual value for enzyme controlled reactions.

A

2

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41
Q

Explain why increasing the temperature up from the optimum decreases the rate of reaction abruptly. (F)

A
  • heat affects the secondary structure of the enzyme
  • strains and breaks the hydrogen bonds
  • enzyme loses shape (tertiary structure) and denatures
  • active site no longer complementary to substrate
  • can no longer form enzyme-substrate complex
42
Q

Describe a graph showing how pH affects the initial rate of an enzyme-controlled reaction.

A
  • steep increase in gradient from pH close to optimum pH
  • peak at optimum pH
  • steep decrease in gradient after optimum pH
43
Q

Explain why a pH change away from the optimum decreases the rate of reaction. (F)

A
  • pH is governed by concentration of H^+ ions
  • interacts with ionic bonds and hydrogen bonds
  • changes tertiary shape
44
Q

Explain why Siamese cats are white with black tails, ears, paws and faces. (S+C)

A
  • tyrosinase (melanin-production enzyme)
  • denatured at body temperature
  • extremities are at lower temperature, so enzyme is not denatured
  • more melanin is produced
45
Q

Describe a graph showing how substrate concentration affects the initial rate of an enzyme-controlled reaction.

A
  • initially has a steep gradient
  • gradient becomes shallower over time
  • levels off and becomes flat
46
Q

Define the term “Vmax”.

A

The maximum rate of an enzyme-catalysed reaction.

47
Q

Explain how increasing the substrate concentration affects the initial rate of an enzyme-controlled reaction. (F)

A
  • increased concentration leads to higher collision rate with enzymes and more enzyme-substrate complexes formed
  • levels off at Vmax where all the active sites are occupied by substrate particles and no more enzyme-substrate complexes can be formed
48
Q

Describe a graph showing how enzyme concentration affects the initial rate of an enzyme-controlled reaction.

A
  • straight line increasing in gradient
49
Q

Explain how increasing the enzyme concentration affects the initial rate of an enzyme-controlled reaction. (F)

A
  • increased concentration leads to higher collision rate with substrate and more enzyme-substrate complexes formed
  • levels off at Vmax where all the substrate particles are bonded to enzymes (no longer a substrate excess)
50
Q

Describe the components of a well-designed experiment.

A
  • only changing the independent variable
  • accurate method of measuring dependent variable
  • all other control variables kept the same
  • repeats
51
Q

Describe how to evaluate an experimental design (including limitations of the experiment).

A
  • consider range of the independent variable
  • accuracy of measuring instruments
  • sufficient number of repeats
  • potential lack of control for controlled variables
52
Q

Describe how to identify possible improvements to an experimental design.

A
  • improve accuracy

- improve repeatability

53
Q

Describe and explain how to investigate any of the factors that affect the rate of enzyme-controlled reactions. (F)

A
  • measure disappearance of reactant or appearance of product
  • i.e. catalase
  • measure volume of O2 produced by subtracting the mass of the test tube after reaction from the initial mass
  • alter different factors e.g. different water baths, different buffer solutions, different ratios of enzyme:substrate concentrations
  • find rate of reaction by dividing mass by time taken
  • plot on graph
54
Q

Describe how to plot two variables from data into an appropriate graphical form.

A

Independent variable on x-axis, dependent variable on y-axis

55
Q

Define the term “anomaly”.

A

A result that deviates from what is expected (outlier).

56
Q

Explain how to identify anomalies in experimental measurements.

A

When a result differs from the other results achieved, or does not fit with the hypothesis.

57
Q

Describe how anomalies can be dealt with.

A

Do repeats and find averages without including the anomaly.

58
Q

State the equation for a straight line.

A

y = mx + c

59
Q

State the meaning of the terms “m” in the equation for a straight line.

A

Gradient

60
Q

Describe how to find “m” from a graph.

A

Change in y / change in x

61
Q

State the meaning of the terms “c” in the equation for a straight line.

A

Y-intercept

62
Q

Describe how to find “c” from a graph.

A

Where the graph crosses the y-axis

63
Q

Explain how to calculate a rate of change from a graph showing a linear relationship (and how to determine suitable units).

A

Change in y / change in x

64
Q

Explain how to estimate a rate of change at a particular point on a graph showing a non-linear relationship.

A

Draw a tangent at the particular point (a line that touches the curve at only one point) and calculate the gradient of the tangent.

65
Q

Describe how to clearly describe data from a graph or a table. (F)

A
  • refer to the point(s) where it is occurring
  • state all data
  • describe overall trends
66
Q

Describe the considerations that need to be taken into account when drawing conclusions from data.

A
  • use entire graph

- consider likelihood of mistakes

67
Q

Define the term “cofactor”. (F)

A

Non-protein component necessary for the effective functioning of an enzyme

68
Q

Define the term “coenzyme”. (F)

A

An organic cofactor

69
Q

Give two possible roles of cofactors/coenzymes. (F)

A
  • transfer atoms or groups from one reaction to another

- form part of the active site

70
Q

Describe the similarities between cofactors, coenzymes and prosthetic groups.

A
  • essential for effective enzyme function
71
Q

Describe the differences between cofactors, coenzymes and prosthetic groups.

A
  • cofactors and coenzymes may be temporarily bound to an enzyme, but a prosthetic group is permanently bound
  • coenzyme is always organic, cofactor is always inorganic, prosthetic group can be either
72
Q

Explain why the chloride ion necessary for the correct formation of the active site in amylase is called a cofactor not a coenzyme or prosthetic group.

A
  • cofactor because it is an inorganic ion
  • not a coenzyme because it is inorganic
  • not a prosthetic group because it is not permanently bound to the active site of the enzyme
73
Q

Explain why the zinc ion that forms an important part of the structure of carbonic anhydrase (an enzyme necessary of the metabolism of carbon dioxide) is called a prosthetic group not a cofactor or coenzyme.

A
  • permanently bound to the active site of the enzyme

- cofactor and coenzyme are be temporarily bound to an enzyme

74
Q

Give two examples of coenzymes that are synthesised from vitamins in our diet.

A
  • NAD (vitamin B3) [responsible for transfer of H atoms between molecules in respiration]
  • coenzyme A (vitamin B5) [ essential in breakdown of fatty acids and carbohydrates in respiration]
75
Q

Describe 4 ways in which multi-step reaction pathways can be regulated by cells.

A
  • competitive inhibition
  • non-competitive inhibition
  • end-producy inhibition
  • inactive precursor enzymes
76
Q

Define the terms “enzyme inhibitor”. (F)

A

Molecules that prevent enzymes from carrying out their normal function of catalysis.

77
Q

Define the terms “competitive inhibitor”. (F)

A

An inhibitor that competes with the substrate to bind to the active site on an enzyme.

78
Q

Define the terms “non-competitive inhibitor”. (F)

A

An inhibitor that binds to an enzyme at an allosteric site.

79
Q

Define the terms “reversible inhibitor”. (F)

A

An inhibitor that binds temporarily to the active site of the enzyme.

80
Q

Define the terms “irreversible inhibitor”. (F)

A

An inhibitor that binds permanently to the active site of the enzyme.

81
Q

Define the terms “allosteric site”. (F)

A

The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active.

82
Q

Explain how a competitive inhibitor affects the rate of an enzyme-controlled reaction. (F)

A
  • rate of reaction decreases
  • has a similar shape to substrate so can fit into the active site of the enzyme
  • blocks substrate from entering active site
  • enzyme cannot carry out its function
  • substrate and inhibitor molecules compete to bind with active sites
83
Q

State two examples of competitive inhibitors and describe their action.

A
  • statins: inhibit synthesis of cholesterol

- aspirin: irreversibly inhibits active site of COX enzymes, preventing synthesis of chemicals producing pain and fever

84
Q

Explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction. (F)

A
  • rate of reaction decreases
  • inhibitor binds to allosteric site of an enzyme
  • changes tertiary structure of an enzyme so active site changes shape
  • active site no longer complementary to substrate
  • enzyme cannot carry out function
85
Q

State two examples of non-competitive inhibitors and describe their action

A
  • organophosphates: irreversibly inhibit enzyme necessary for nerve impulse transmission
  • proton pump inhibitors (PPIs): irreversibly block enzyme system responsible for secreting H^+ into stomach
86
Q

Describe a graph showing how substrate concentration affects the rate of an enzyme-controlled reaction if a competitive inhibitor is present.

A
  • less steep gradient than without inhibitor
87
Q

Describe a graph showing how substrate concentration affects the rate of an enzyme-controlled reaction if a non-competitive inhibitor is present.

A
  • less steep gradient than without inhibitor
88
Q

Explain the effect of competitive inhibitors on the Vmax of an enzyme-controlled reaction.

A
  • Vmax stays the same

- if substrate concentration is increased enough, can overcome effect of inhibitor

89
Q

Explain the effect of non-competitive inhibitors on the Vmax of an enzyme-controlled reaction.

A
  • Vmax decreases

- substrate concentration does not affect inhibitor’s ability to inhibit enzyme

90
Q

Define the term “end-product inhibition”. (F)

A

The product of a reaction inhibits the enzyme required for the reaction.

91
Q

Describe the usefulness of end-product inhibition in controlling metabolic pathways. (F)

A
  • negative feedback control mechanism
  • no excess product made and no resources wasted
  • if there is little product, more will be made
  • if there is too much product, it inhibits its own production
92
Q

Describe how ATP is involved in end-product inhibition of the enzyme phosphofructokinase (PFK). (S+C)

A
  • PFK catalyses breakdown of glucose molecule
  • high ATP levels: binds to allosteric site on PFK so glucose is not broken down
  • as ATP is used up, less binds to PFK and enzyme catalyses breakdown of glucose so more ATP is produced
93
Q

Define the term “inactive precursor enzyme”.

A

An inactive enzyme that can be turned into an active form by further modification.

94
Q

Explain why enzymes may be produced in as inactive precursors.

A
  • to prevent causing damage within cells producing them or tissues where they are released
  • action needs to be controlled and only activated under certain conditions
95
Q

Describe three ways in which inactive precursor may be activated.

A
  • change in shape i.e. by addition of a cofactor
  • action of another enzyme i.e. protease to cleave bonds in structure
  • change in conditions i.e. pH or temperature
96
Q

Define the term “apoenzyme”.

A

An inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor

97
Q

Define the term “holoenzyme”.

A

An enzyme with its required cofactor

98
Q

Define the term “zymogens”.

A

An inactive substance which is converted into an enzyme when activated by another enzyme.

99
Q

Define the term “proenzymes”.

A

A biologically inactive substance which is metabolized into an enzyme.

100
Q

Give 2 examples of inactive precursor enzymes and describe how they are activated.

A
  • inactive pepsinogen: released into stomach to digest proteins, acid pH activates it to form pepsin (protects body tissues)
  • Factor X: activated by cofactor vitamin K to catalyse prothrombin into thrombin by cleaving bonds

Biology (23 decks)

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