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WorksheetsChapter 3 - Enzymes MCQs (2015 Past Year)
Total questions: 20
Worksheet time: 12mins
[CIE, Nov 2015, P13, Q12]
The graph shows the concentration of one of the substances which is involved in an enzyme-catalysed reaction. Which substance is shown by line X?
enzyme
enzyme-product complex
enzyme-substrate complex
substrate
[CIE, Nov 2015, P13, Q13]
What describes the induced fit mode of action of an enzyme?
The binding of the active site to the substrate causes the enzyme to change shape.
The substrate and active site have complementary shapes that form temporary bonds.
The substrate causes a change in enzyme shape so the active site can bind.
The substrate changes shape so it can bind to the active site.
[CIE, Nov 2015, P13, Q14]
Line X represents the course of an enzyme-catalysed reaction under optimum conditions.
Line Y shows the action of the same enzyme on the same substrate but with one variable changed: substrate concentration or pH or temperature.
Which changes to the variables could give the results shown by line Y?
decreased substrate concentration
higher pH
lower temperature
[CIE, Nov 2015, P12, Q12]
Which statements describe some enzyme actions?
Enzymes hold reacting molecules in such a way that their reactive groups are brought close together.
In an enzyme-catalysed reaction, more molecules have sufficient energy to react than in the absence of the enzyme.
Reactions catalysed by enzymes take place at a lower temperature than they would without the enzyme.
[CIE, Nov 2015, P12, Q13]
The diagram shows the mass of product formed over time in three reactions using the same substrate and enzyme.
The volumes of substrate, enzyme and temperature were kept constant in each reaction. Which statement explains the difference in these reactions?
The pH in reactions 2 and 3 has denatured the enzyme.
There is a non-competitive inhibitor present in reaction 3.
There is the highest concentration of enzyme in reaction 1.
There is the highest concentration of substrate in reaction 1.
[CIE, Nov 2015, P12, Q14]
Tyrosinase is an enzyme that catalyses the conversion of the amino acid tyrosine into the black pigment melanin. It is responsible for the black fur colour of some rabbits.
A group of rabbits kept at 30 °C resulted in 90% of the rabbits with light fur colour. A second group of rabbits kept at 10 °C resulted in 90% of the rabbits with black fur colour.
Which hypothesis is supported by these results?
An inhibitor is present in rabbit skin cells that can bind strongly to tyrosinase when the external temperature is 30 °C.
At 10 °C external temperature there are fewer tyrosinase-tyrosine complexes formed and less melanin is produced.
Tyrosinase is an enzyme that is coded for by a gene that is switched off when the external temperature is 10 °C.
Tyrosinase is a temperature-sensitive molecule that is only activated when the external temperature is 30 °C.
[CIE, Nov 2015, P11, Q12]
The graph shows the energy levels involved in an enzyme-catalysed reaction. Substrate molecules X and Y combine to give product Z.
Which arrow shows the reduction in activation energy due to the enzyme?
A
B
C
D
[CIE, Nov 2015, P11, Q13]
Which statements about enzyme inhibitors are correct?
Competitive inhibitors may be similar shapes to the substrate.
Competitive inhibitors bind to the active site.
Non-competitive inhibitors alter the shape of the enzyme.
Non-competitive inhibitors bind to the substrate.
[CIE, Nov 2015, P11, Q14]
A fixed volume of the enzyme catalase was added to a fixed volume of hydrogen peroxide solution. The diagram shows how the amount of product changed over the course of the reaction.
What explains the shape of this graph?
The active sites become saturated.
The enzyme was denatured.
The hydrogen peroxide inhibited the reaction.
The substrate molecules were used up.
[CIE, June 2015, P13, Q14]
The enzyme DNA polymerase is used in DNA replication. This enzyme was extracted from bacteria living in natural hot water springs where the water temperature is between 85 °C and 95 °C.
Which graph would represent the relationship between temperature and the rate of DNA replication when catalysed by the enzyme from these bacteria?
A
B
C
D
[CIE, June 2015, P12, Q14]
Which statements are true about the optimum temperature of all enzymes?
It is the temperature at which the enzymes work best.
It is the highest temperature at which the enzyme will work.
It is between 35 °C and 40 °C.
[CIE, June 2015, P11, Q13] [CIE, Nov 2011, P11, Q12]
Which statements about the effect of all enzyme inhibitors are correct?
change the shape of the active site
denature the enzyme
reduce the rate of the enzyme-catalysed reaction
[CIE, June 2015, P11, Q14]
The graphs show the rate of reaction of an enzyme-catalysed reaction.
Which graph shows the effect of increasing the concentration of the substrate at two different concentrations of a competitive inhibitor?
A
B
C
D
[CIE, Nov 2014, P13, Q12]
A quantity of an enzyme was added to a quantity of its substrate. The graphs show the changes in concentration of the enzyme, the substrate, the enzyme-substrate complex and the product over time.
Which graph shows the change in the concentration of the enzyme-substrate complex?
A
B
C
D
[CIE, Nov 2014, P12, Q14]
Lipase is a digestive enzyme produced by the pancreas that catalyses the hydrolysis of dietary lipids. The table shows how the pH of a liquid food containing a high proportion of lipids decreases over time.
Which statements are possible explanations of the results of the experiment between 50 and 60 minutes?
Enzyme concentration becomes the limiting factor.
Substrate concentration becomes the limiting factor.
All the enzyme active sites are saturated.
Denaturation of the enzyme by the products.
Products are acting as competitive inhibitors.
[CIE, Nov 2014, P11, Q11]
Why do large increases in the temperature or pH alter enzyme activity?
They change the three-dimensional shape of the enzyme.
They disrupt hydrogen and ionic bonds in the enzyme.
They increase hydrophobic interactions in the enzyme.
[CIE, Nov 2014, P11, Q12]
Ethylene glycol is a chemical used to prevent water from freezing. If ethylene glycol is swallowed accidentally, it is metabolised by an enzyme found in liver cells to produce a toxic product.
The enzyme normally catalyses the oxidation of ethanol to a harmless product.
People who have swallowed ethylene glycol are treated with large doses of ethanol. This prevents formation of a toxic product and allows the body to excrete the ethylene glycol.
Which statement describes why this treatment works?
Ethanol binds near the active site on the enzyme, altering its shape.
Ethanol binds permanently to the active site of the enzyme, blocking it.
Ethanol changes the tertiary structure of the enzyme, denaturing it.
Ethanol is more likely to bind to the active site on the enzyme.
[CIE, June 2014, P11, Q12]
The statements are about enzymes. Which statements are correct for all enzymes?
They are globular proteins.
They are formed in the smooth endoplasmic reticulum.
They are only found attached to plasma membranes in the cell.
They can be inhibited by competitive inhibitors.
[CIE, June 2014, P12, Q13]
The drug ritonavir is sometimes used in the treatment of HIV / AIDS.
Ritonavir consists of three amino acids and is a competitive inhibitor of HIV protease. HIV causes this protease to be made inside human cells.
Ritonavir produces many side effects as it interferes with many metabolic processes in human cells.
Which statements about ritonavir are correct?
Ritonavir has a shape complementary to the active site of HIV protease.
Ritonavir will enter human cells directly through the lipid bilayer and not require any transport proteins.
Ritonavir is likely to inhibit many of the enzymes of human cells.
Complete hydrolysis of ritonavir would require the addition of three water molecules.
[CIE, June 2014, P13, Q13]
The graph shows the rate of activity of the enzyme sucrase plotted against the concentration of sucrose. Why does the rate of enzyme activity remain constant from 80 – 90 g dm–3?
All the enzyme has been inhibited.
All the substrate has been used up.
The concentration of the enzyme is limiting the rate.
The concentration of the substrate is limiting the rate.
