3.1. Mode of action of enzymes
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 74 questions
Tobacco smoking is known to be associated with atherosclerosis and emphysema. Outline ways in which tobacco smoking can contribute to atherosclerosis. is a scan of the lungs of a person with emphysema. One common feature in the damaged areas labelled is a loss of the elastic fibres of the alveoli. Another feature is an increased number of macrophages and neutrophils. damaged area of right lung State the general role shared by macrophages and neutrophils. Suggest how the loss of the elastic fibres would cause the enlargement of the lung shown in . The synthesis and release of elastase enzymes by macrophages and neutrophils is an important feature in the development and progression of emphysema. Elastase causes the breakdown of the protein elastin, the main component of elastic fibres. Explain what is meant by an enzyme. Elastase has an active site with a specific shape. The mode of action of this enzyme supports the lock and key hypothesis. Explain the mode of action of elastase. You may use the space below to draw a diagram or diagrams to help your answer. There are two inhibitors of elastase that are produced in the body, TIMP-1 and A1AT: • macrophage elastase is inhibited by TIMP-1 • neutrophil elastase is inhibited by A1AT. The inhibitors can be inactivated by the elastase enzymes: • macrophage elastase can inactivate A1AT • neutrophil elastase can inactivate TIMP-1. In healthy lungs, the activity of elastase enzymes is regulated. Tobacco smoke can disrupt this regulation. One effect of tobacco smoke is to cause changes in the structure of A1AT, a competitive inhibitor. Suggest how structural changes to A1AT will affect its mode of action. A1AT is a protein. Some non-smokers have a mutation in the gene coding for A1AT and are at risk of developing emphysema as there is a lack of A1AT in the lung tissue. Explain why a lack of A1AT in these non-smokers means that they are at risk of developing emphysema. Tobacco smoke is known to cause increased production of macrophage elastase. MMP12 is the gene coding for macrophage elastase. Copies of this gene are produced as messenger RNA (mRNA). Describe how this mRNA is used in translation to produce macrophage elastase.
9700_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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The enzyme catalase is found in many plant and animal tissues. The enzyme catalyses the decomposition of hydrogen peroxide, which is a toxic product of metabolism. The reaction is: catalase 2H2O2 O2 + 2H2O A research team investigated the activity of two forms of catalase, P and Q, extracted from Anopheles gambiae, an important vector of malaria. The team investigated the effect of increasing concentrations of hydrogen peroxide on the activity of these two forms of catalase. The results are shown in . concentration of hydrogen peroxide / mM activity of catalase / arbitrary units catalase P catalase Q With reference to , describe and explain the effect of increasing the concentration of hydrogen peroxide on the activity of catalase P. Each molecule of catalase consists of four identical polypeptides. The two forms of catalase in A. gambiae differ by only one amino acid at position 2 in the amino acid sequence. Catalase P has serine and catalase Q has tryptophan. Suggest how the difference in one amino acid is responsible for the lower activity of catalase Q compared with catalase P. Female mosquitoes feed on blood in order to produce their eggs. After feeding, the metabolic rate increases for egg production. The researchers allowed female mosquitoes to feed on blood. They found that female mosquitoes with only catalase P produced more eggs than those with only catalase Q. Suggest why there is a difference in egg production between the two types of A. gambiae. Metal ions can act as a non-competitive inhibitor of catalase. Explain how copper ions can act as a non-competitive inhibitor. Enzyme inhibitors can also inhibit carrier proteins in cell surface membranes. Explain why carrier proteins are required in cell surface membranes. Describe three roles of cell surface membranes, other than the transport of substances into and out of cells. 1. 2. 3.
9700_w15_qp_23
THEORY
2015
Paper 2, Variant 3
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shows the structure of the enzyme lysozyme. s s s s s s s s Lys Trp Trp Trp Val Gly Gly Gly Gly Gly Gly Gly Gly Gly Gly Gly Gly Arg Cys Glu Leu Ala Ala Ala Ala Ala Ala Gln Gln Ile Ile Ile Ile Pro Pro Ile Ile Gln Ala Ala Ala Ala Ala Ala Leu Asp Asn Tyr Tyr Ser Ser Ser Ser Ser Ser Ser Ser Ser Ser Tyr Asn Asn Asn Thr Thr Thr Thr Thr Thr Asn Asn Asn Asn Asn Asn Asn Asn Asn Asp Asp Thr Asp Asp Asp Asp Asp Leu Leu Leu Leu Leu Leu Glu Cys Cys Cys Cys Cys Cys Cys Arg His Arg Arg Arg Trp Trp Trp Arg Arg Arg Arg Arg Arg Phe Phe Phe Val Val Val Val Val Lys Met Met Lys Lys Lys Lys Name the two types of covalent bond in the structure in . The primary structure of lysozyme is shown in . Explain the meaning of the term primary structure. Lysozyme hydrolyses the β-1,4 glycosidic bonds present in compounds found in bacterial cell walls. State what is meant by the term hydrolysis. Suggest the type of biological molecule which is the substrate for lysozyme. Lysozyme uses the induced fit mechanism. Explain the mode of action of an enzyme that uses the induced fit mechanism. In human tears and saliva, lysozyme acts as an extracellular enzyme. State what is meant by the term extracellular. shows the results of an investigation into the effect of substrate concentration on the rate of reaction catalysed by lysozyme. substrate concentration / mmol rate of reaction / μmol min–1 Use to: state the lowest substrate concentration to give the maximum rate of reaction, Vmax determine the Michaelis-Menten constant, Km. Km = The investigation was repeated in the presence of a competitive inhibitor of lysozyme. Draw a curve on to show the expected results.
9700_w16_qp_21
THEORY
2016
Paper 2, Variant 1
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Telomerase is an enzyme that is important in maintaining the telomeres that are located at the ends of chromosomes. Explain the importance of telomeres. Suggest why telomerase is present in much higher quantities in stem cells and cancer cells than in other cell types. Studies suggest that telomerase is a flexible molecule when binding its substrate. The active site changes its shape slightly to allow the formation of the enzyme-substrate complex. Name the theory that describes this mode of enzyme action. An investigation was carried out into the effect of substrate concentration on the activity of telomerase. The results are shown in . 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 rate of reaction / arbitrary units substrate concentration / μmol dm–3 With reference to , explain the difference in the rates of reaction obtained for telomerase at a substrate concentration of 0.2 μmol dm−3 compared with a substrate concentration of 1.6 μmol dm−3.
9700_w19_qp_22
THEORY
2019
Paper 2, Variant 2
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Questions Discovered
74