Syllabus Edition
First teaching 2014
Last exams 2024
1 markWhich of the following statements is not true about enzymes in metabolic pathways?
All metabolic reactions are catalysed by an enzyme.
All proteins are enzymes.
All enzymes are proteins.
All enzymes reduce activation energy of metabolic reactions in living organisms.
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1 markThe following statements are about enzymes:
Which of these statements are correct for all enzymes?
1 and 3 only
1, 2 and 3 only
2, 3 and 4 only
All of them are correct
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1 markWhich of the following sketch graphs best shows the effect of an enzyme on a biochemical reaction profile?
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1 markWhich one of the following phenomena is not a consequence of end-product inhibition in biochemical pathways?
Regulation of the pathway.
Prevention of a build-up of biochemical intermediate compounds.
Shutdown of the pathway once product levels reach zero.
Allosteric changes to an enzyme involved in the pathway.
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1 markEnzymes alter the activation energy required for a biochemical reaction to take place. Which of the following gives the best definition of activation energy?
The energy input required to break bonds in order for a reaction to take place.
The energy is released as bonds breaks in a reaction.
The energy required to allow substrates and enzymes to be closely aligned at the active site.
The energy given off when an enzyme-substrate complex forms.
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1 markThis diagram shows a metabolic pathway occurring in an organelle. The speed of this metabolic pathway is self-regulating as the end product acts as a competitive inhibitor to enzyme 2.
| enzyme 1 | enzyme 2 | enzyme 3 | ||||
| reactant | → | intermediate X | → | intermediate Y | → | end product |
What would you expect not to occur when adding an additional end product to the organelle?
Enzyme 2's activity will decrease
The amount of intermediate Y would decrease
The amount of reactant would increase
The amount of intermediate X would increase
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1 markIn the graph, Z represents the relationship between the initial rate of an enzyme-catalysed reaction and the concentration of its substrate under optimal conditions and without an inhibitor.
Which curve would represent the same experiment carried out in the presence of a low concentration of a non-competitive inhibitor?
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1 markThe graphs in A - D show the progress of an enzyme-catalysed reaction, measured by the volume of product released from the reaction mixture over time.
Which graph best depicts how a scientist would establish the average rate of reaction over the first minute of the reaction?
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1 markThe following six statements are steps in using bioinformatics to find potential cures for malaria, one of the most serious infectious diseases that humans face. The steps are not listed in the correct order below.
1. Computer modelling of candidate molecules to identify strong candidates
2. Determining the malaria parasite's proteome
3. Identifying candidate molecules that could inhibit malaria parasite enzymes
4. Sequencing the malaria parasite's genome
5. Drug trials to establish safety and efficacy
6. Identification of malaria parasite enzymes that could be targets
Which of A - D places the statements into chronological order?
4 → 2 → 6 → 3 → 1 → 5
2 → 4 → 3 → 5 → 6 → 1
4 → 2 → 3 → 5 → 1 → 6
2 → 6 → 4 → 5 → 3 → 1
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1 markThe enzyme catalase was added to a large volume of hydrogen peroxide solution. The volume of oxygen produced in the first five seconds was measured at 250 cm3.
What is the initial rate of reaction in dm3 min-1 ?
50 dm3 min-1
3 dm3 min-1
0.05 dm3 min-1
3 000 dm3 min-1
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Which of the following statements about metabolism are correct?
I and IV only
II and III
All of the statements
I, II and III
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Which of the following is not a correct description of the “transition state” in enzyme-controlled reactions?
The enzyme-substrate complex, prior to the products being formed, can be said to be in the transition state.
The enzyme-product complex, prior to the products being released, can be said to be in the transition state.
The transition state occurs when a substrate binds to the enzyme’s active site.
Transition state is a temporary state
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The graph below shows the energy changes during a reaction.
What effect would adding an enzyme have on the energy changes of the reaction?
Reduction in energy at A
Reduction in energy at B
Reduction in energy at C
Reduction in energy at D
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What is the difference between a competitive and non-competitive inhibitor?
|
Competitive inhibitor |
Non-competitive inhibitor |
|
| A |
Interferes with active site |
Interferes with an alternative site |
| B |
Interferes with an alternative site |
Interferes with the active site |
| C |
Changes the active site |
Changes the substrate |
| D |
Changes the substrate |
Changes the active site |
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Cyanide ions are an example of an allosteric inhibitor that targets the enzyme cytochrome c oxidase in aerobic respiration.
Which row best describes the action of cyanide ions?
|
Can bind to an alternative site |
Can bind to the active site |
|
| A |
Yes |
Yes |
| B |
Yes |
No |
| C |
No |
Yes |
| D |
No |
No |
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Isoleucine can be described as an end-product inhibitor.
Which statement best describes the action of isoleucine?
It acts as a competitive inhibitor to threonine and it binds to an allosteric site on threonine deaminase.
It acts as a competitive inhibitor to threonine and it binds to the active site on threonine deaminase.
It acts as a non-competitive inhibitor to threonine and it binds to an active site on threonine deaminase.
It acts as a non-competitive inhibitor to threonine and it binds to an allosteric site on threonine deaminase.
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The protein sequence of an enzyme involved in the Plasmodium parasite’s metabolism has been identified in order to support research into anti-malarial drugs.
Which terms best fill the gaps in the sentence about Plasmodium parasite research below?
Bioinformatics can be used to screen ………I……….. against a database of chemicals to identify potential ………II………..
|
I |
II |
|
| A |
Enzymes |
Enzyme inhibitors |
| B |
Proteomes |
Products |
| C |
Enzymes |
Active sites |
| D |
Proteomes |
Substrates |
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Which graph shows the rate of a reaction taking place in the presence of a competitive inhibitor compared to the rate of a reaction in the absence of an inhibitor?
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The table below gives information on the rates of several enzyme-catalysed reactions.
|
Rate of reaction / product formed sec⁻¹ |
Enzyme |
|
1.0 x 10⁶ |
Citrate synthase |
|
5.2 x 10³ |
Aconitase |
|
9.2 x 10⁴ |
Fumarase |
|
3.7 x 10⁷ |
Malate dehydrogenase |
Which enzyme catalyses the reaction with the fastest rate of product formation?
Citrate synthase
Aconitase
Fumarase
Malate dehydrogenase
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Which statement best describes how to calculate the initial rate of a reaction from a graph such as the one below?
Draw a tangent that crosses the origin and that corresponds to the first part of the curve, calculate the rate by dividing change in volume by change in time.
Draw a tangent that corresponds to an area part way along the curve, calculate the rate by dividing change in volume by change in time.
Draw a tangent that crosses the origin and that corresponds to the first part of the curve, calculate the rate by dividing change in time by change in volume.
Draw a tangent that corresponds to an area part way along the curve, calculate the rate by dividing change in time by change in volume
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