3.1. Mode of action of enzymes
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 74 questions
Enzymes are polymers of amino acids. Complete to show the general structure of an amino acid. O C C H N When bananas are peeled, the exposed tissue gradually turns brown in the presence of oxygen in the air. This is due to an enzyme called catechol oxidase, which acts on the substrate catechol. Catechol and catechol oxidase are present in the banana tissue. The overall reaction is shown in . catechol catechol oxidase melanin oxygen A student investigated how the concentration of catechol oxidase affects the rate of this reaction. All other variables were kept constant throughout the investigation. For each concentration of catechol oxidase used, the student mixed catechol oxidase solution with catechol and recorded the time taken for the mixture to reach a standard brown colour. The rate of reaction, R, for each concentration of catechol oxidase used was then calculated using the formula: R = time to reach standard brown colour in minutes Calculate the rate of reaction when the standard brown colour was reached in 2 minutes 30 seconds. rate of reaction = min–1 is a graph showing the results of the investigation. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 rate of reaction / min–1 percentage concentration of catechol oxidase State how the results shown in show that substrate was in excess at all concentrations of catechol oxidase tested. The student carried out a further experiment to investigate how the concentration of catechol affects the initial rate of reaction. All other variables were kept constant throughout this investigation. is a graph showing the effect of varying the concentration of catechol on the initial rate of reaction. 0.0 0.00 0.20 0.40 0.60 catechol concentration / mol dm–3 0.80 1.00 1.20 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 initial rate of reaction / min–1 Explain the shape of the curve shown in . Use to calculate the value of the Michaelis–Menten constant (Km) for the reaction between catechol oxidase and catechol. Km = mol dm–3 Methylcatechol has a similar shape to catechol. Catechol oxidase can also use methylcatechol as a substrate. The Km value for the reaction using methylcatechol as the substrate was found to be much lower than the Km value for the reaction using catechol as the substrate, when the reactions were carried out under the same conditions. State what these Km values indicate about the relationship between the enzyme and the two substrates.
9700_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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Penicillin is an antibiotic that interferes with the synthesis of cell walls in bacteria. Even before penicillin became widely available in the 1940s, the enzyme penicillinase which breaks down penicillin had been isolated. This enzyme is now found in many bacteria and gives them resistance to penicillin. is a ribbon model of the structure of the enzyme penicillinase. The arrow indicates the active site of the enzyme. Explain why the shape of the active site of an enzyme, such as penicillinase, is important. With reference to , identify the aspects of protein structure that are shown and those that are not shown. aspects of protein structure shown aspects of protein structure not shown shows the changes in energy during the progress of an uncatalysed reaction. progress of the reaction energy Draw on a curve to show changes in energy during the progress of the same reaction when catalysed by an enzyme. State the term given to the energy level that must be overcome before a reaction can progress. Antibiotic resistance is a serious worldwide problem. Suggest how antibiotics can be used effectively to avoid the development of widespread resistance in bacteria.
9700_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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Questions Discovered
74