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.
2
Q
Define the term “substrate”. (F)
A
A substance used, or acted on, by another process or substance i.e. a reactant.
3
Q
Define the term “product”. (F)
A
The molecule(s) that is formed by a reaction.
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.
5
Q
Define the term “anabolic reactions”.
A
Reactions of metabolism that construct molecules from smaller units, requiring energy.
6
Q
Define the term “catabolic reactions”.
A
Reactions of metabolism that break molecules down into smaller units, releasing energy.
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.
8
Q
Define the term “metabolism”.
A
The chemical processes that occur within a living organism in order to maintain life.
9
Q
Define the term “intracellular enzyme”. Give one example.
A
An enzyme that acts inside the cell e.g. catalase.
10
Q
Define the term “extracellular enzyme”. Give two examples.
A
An enzyme that acts outside the cell e.g. amylase, trypsin.
11
Q
State the substrate for the enzyme catalase. (F)
A
Hydrogen peroxide (H2O2)
12
Q
State the substrate for the enzyme amylase. (F)
A
Starch
13
Q
State the substrate for the enzyme trypsin. (F)
A
Protein
14
Q
State the products for the enzyme catalase. (F)
A
Oxygen and water
15
Q
State the products for the enzyme amylase. (F)
A
Glucose
16
Q
State the products for the enzyme trypsin. (F)
A
Polypeptides (amino acids by other enzymes)
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.
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
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
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.
21
Q
Define the term “complementary shape”. (F)
A
The shape of the active site and the substrate match so they can fit together.
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.
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.
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
25
Describe the “lock and key” hypothesis of enzyme action. (F) ***
- 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
26
Describe the “induced-fit” hypothesis of enzyme action. ***
- active site of the enzyme changes shape slightly
- changes in enzymes tertiary structure strengthen binding
- puts strain on substrate molecule and weakens bonds
27
Suggest how the R-groups of amino acids are involved in catalysing reactions.
Interactions between R-groups in tertiary structure affect the shape of the active site and which substrates it can catalyse reactions for
28
Define the term “activation energy”. (F)
The energy required to initiate a reaction.
29
Define the term “rate of reaction”. (F)
How quickly the reaction takes place.
30
State what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.
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.
31
State 5 factors that affect the rate of an enzyme controlled reaction. (F)
- enzyme concentration
- substrate concentration
- temperature
- pH
- inhibitors
32
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.
- initially has steep gradient
| - levels out to be flat
33
Explain the shape of a graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time.
- 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
34
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.
The gradient is the rate of reaction.
35
Define the term “initial rate of reaction”.
The speed of the reaction at the start of the reaction (t=0)
36
Describe the significance of the initial rate of reaction in investigations into factors affecting the rate of enzyme-controlled reactions.
The initial rate of reaction is used to compare how the enzyme-controlled reactions differ when a factor is changed.
37
Describe a graph showing how temperature affects the initial rate of an enzyme-controlled reaction.
- 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
38
Explain why increasing the temperature from below the optimum up towards the optimum increases the rate of reaction. (F)
- 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
39
Define the term “temperature coefficient, Q10”.
A measure of how much the rate of a reaction increases with a 10°C temperature increase.
40
State the temperature coefficient's usual value for enzyme controlled reactions.
2
41
Explain why increasing the temperature up from the optimum decreases the rate of reaction abruptly. (F)
- 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
Describe a graph showing how pH affects the initial rate of an enzyme-controlled reaction.
- steep increase in gradient from pH close to optimum pH
- peak at optimum pH
- steep decrease in gradient after optimum pH
43
Explain why a pH change away from the optimum decreases the rate of reaction. (F)
- pH is governed by concentration of H^+ ions
- interacts with ionic bonds and hydrogen bonds
- changes tertiary shape
44
Explain why Siamese cats are white with black tails, ears, paws and faces. (S+C)
- tyrosinase (melanin-production enzyme)
- denatured at body temperature
- extremities are at lower temperature, so enzyme is not denatured
- more melanin is produced
45
Describe a graph showing how substrate concentration affects the initial rate of an enzyme-controlled reaction.
- initially has a steep gradient
- gradient becomes shallower over time
- levels off and becomes flat
46
Define the term “Vmax”.
The maximum rate of an enzyme-catalysed reaction.
47
Explain how increasing the substrate concentration affects the initial rate of an enzyme-controlled reaction. (F)
- 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
Describe a graph showing how enzyme concentration affects the initial rate of an enzyme-controlled reaction.
- straight line increasing in gradient
49
Explain how increasing the enzyme concentration affects the initial rate of an enzyme-controlled reaction. (F)
- 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
Describe the components of a well-designed experiment.
- only changing the independent variable
- accurate method of measuring dependent variable
- all other control variables kept the same
- repeats
51
Describe how to evaluate an experimental design (including limitations of the experiment).
- consider range of the independent variable
- accuracy of measuring instruments
- sufficient number of repeats
- potential lack of control for controlled variables
52
Describe how to identify possible improvements to an experimental design.
- improve accuracy
| - improve repeatability
53
Describe and explain how to investigate any of the factors that affect the rate of enzyme-controlled reactions. (F)
- 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
Describe how to plot two variables from data into an appropriate graphical form.
Independent variable on x-axis, dependent variable on y-axis
55
Define the term “anomaly”.
A result that deviates from what is expected (outlier).
56
Explain how to identify anomalies in experimental measurements.
When a result differs from the other results achieved, or does not fit with the hypothesis.
57
Describe how anomalies can be dealt with.
Do repeats and find averages without including the anomaly.
58
State the equation for a straight line.
y = mx + c
59
State the meaning of the terms “m” in the equation for a straight line.
Gradient
60
Describe how to find "m" from a graph.
Change in y / change in x
61
State the meaning of the terms “c” in the equation for a straight line.
Y-intercept
62
Describe how to find "c" from a graph.
Where the graph crosses the y-axis
63
Explain how to calculate a rate of change from a graph showing a linear relationship (and how to determine suitable units).
Change in y / change in x
64
Explain how to estimate a rate of change at a particular point on a graph showing a non-linear relationship.
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
Describe how to clearly describe data from a graph or a table. (F)
- refer to the point(s) where it is occurring
- state all data
- describe overall trends
66
Describe the considerations that need to be taken into account when drawing conclusions from data.
- use entire graph
| - consider likelihood of mistakes
67
Define the term “cofactor”. (F)
Non-protein component necessary for the effective functioning of an enzyme
68
Define the term “coenzyme”. (F)
An organic cofactor
69
Give two possible roles of cofactors/coenzymes. (F)
- transfer atoms or groups from one reaction to another
| - form part of the active site
70
Describe the similarities between cofactors, coenzymes and prosthetic groups.
- essential for effective enzyme function
71
Describe the differences between cofactors, coenzymes and prosthetic groups.
- 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
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.
- 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
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.
- permanently bound to the active site of the enzyme
| - cofactor and coenzyme are be temporarily bound to an enzyme
74
Give two examples of coenzymes that are synthesised from vitamins in our diet.
- 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
Describe 4 ways in which multi-step reaction pathways can be regulated by cells.
- competitive inhibition
- non-competitive inhibition
- end-producy inhibition
- inactive precursor enzymes
76
Define the terms “enzyme inhibitor”. (F)
Molecules that prevent enzymes from carrying out their normal function of catalysis.
77
Define the terms “competitive inhibitor”. (F)
An inhibitor that competes with the substrate to bind to the active site on an enzyme.
78
Define the terms “non-competitive inhibitor”. (F)
An inhibitor that binds to an enzyme at an allosteric site.
79
Define the terms “reversible inhibitor”. (F)
An inhibitor that binds temporarily to the active site of the enzyme.
80
Define the terms “irreversible inhibitor”. (F)
An inhibitor that binds permanently to the active site of the enzyme.
81
Define the terms “allosteric site”. (F)
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
Explain how a competitive inhibitor affects the rate of an enzyme-controlled reaction. (F)
- 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
State two examples of competitive inhibitors and describe their action.
- statins: inhibit synthesis of cholesterol
| - aspirin: irreversibly inhibits active site of COX enzymes, preventing synthesis of chemicals producing pain and fever
84
Explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction. (F)
- 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
State two examples of non-competitive inhibitors and describe their action
- organophosphates: irreversibly inhibit enzyme necessary for nerve impulse transmission
- proton pump inhibitors (PPIs): irreversibly block enzyme system responsible for secreting H^+ into stomach
86
Describe a graph showing how substrate concentration affects the rate of an enzyme-controlled reaction if a competitive inhibitor is present.
- less steep gradient than without inhibitor
87
Describe a graph showing how substrate concentration affects the rate of an enzyme-controlled reaction if a non-competitive inhibitor is present.
- less steep gradient than without inhibitor
88
Explain the effect of competitive inhibitors on the Vmax of an enzyme-controlled reaction.
- Vmax stays the same
| - if substrate concentration is increased enough, can overcome effect of inhibitor
89
Explain the effect of non-competitive inhibitors on the Vmax of an enzyme-controlled reaction.
- Vmax decreases
| - substrate concentration does not affect inhibitor's ability to inhibit enzyme
90
Define the term “end-product inhibition”. (F)
The product of a reaction inhibits the enzyme required for the reaction.
91
Describe the usefulness of end-product inhibition in controlling metabolic pathways. (F)
- 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
Describe how ATP is involved in end-product inhibition of the enzyme phosphofructokinase (PFK). (S+C)
- 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
Define the term “inactive precursor enzyme”.
An inactive enzyme that can be turned into an active form by further modification.
94
Explain why enzymes may be produced in as inactive precursors.
- 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
Describe three ways in which inactive precursor may be activated.
- 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
Define the term “apoenzyme”.
An inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor
97
Define the term “holoenzyme”.
An enzyme with its required cofactor
98
Define the term “zymogens”.
An inactive substance which is converted into an enzyme when activated by another enzyme.
99
Define the term “proenzymes”.
A biologically inactive substance which is metabolized into an enzyme.
100
Give 2 examples of inactive precursor enzymes and describe how they are activated.
- 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
