3.2. Factors that affect enzyme action
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 202 questions
Trypsin is an enzyme which catalyses the hydrolysis of casein, a protein found in milk. Milk that contains casein has a cloudy, white appearance. As the casein is hydrolysed by trypsin, the milk changes in appearance to a clear , colourless solution. A student carried out an experiment to investigate the effect of enzyme concentration on the rate at which trypsin hydrolyses casein. The student added a solution of trypsin to a sample of milk and recorded the time taken for the milk to become transparent. The student repeated the experiment with different concentrations of trypsin. All other variables were kept constant. shows the results from the experiment. When the concentration of trypsin increases from 2.0% to 4.0%, the time taken for the milk to become transparent decreases by 48%. Calculate the percentage decrease in the time taken for milk to become transparent when the concentration of trypsin increases from 0.25% to 0.5%. Write your answer to the nearest whole number. percentage decrease Explain the results shown in . Trypsin has the potential to be used in a wide range of industrial processes. The use of immobilised enzymes in industrial processes has many advantages. Scientists investigated the effect of temperature on the activity of trypsin immobilised on the surface of a material and trypsin free in solution. Table 5.1 shows the results of the investigation. Table 5.1 temperature / °C percentage of maximum activity of immobilised trypsin percentage of maximum activity of trypsin free in solution State a reason for the difference in percentage of maximum activity of immobilised trypsin and trypsin free in solution at 25 °C. Suggest and explain why the percentage of maximum activity of immobilised trypsin at 55 °C is higher than the percentage of maximum activity of trypsin free in solution at 55 °C.
9700_w24_qp_21
THEORY
2024
Paper 2, Variant 1
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Azotobacter vinelandii is a bacterium found in the soil that is able to fix atmospheric nitrogen. One feature of nitrogen-fixing bacteria is the ability to synthesise the enzyme nitrogenase, a molybdenum- and iron-containing, protein complex. Molybdenum is a mineral ion found in the soil solution. It enters the cell as molybdate ions, through membrane transport proteins. The proteins have the ability to bind to, and hydrolyse, ATP. Name and describe the mechanism of transport of molybdate ions into the cell. State the structures in the bacterial cell where the protein components of nitrogenase are synthesised. Part of the equation for the reaction that is catalysed by nitrogenase in A. vinelandii is shown below. Complete the equation by naming the product of the reaction. nitrogenase atmospheric nitrogen (N 2 ) ATP and hydrogen Table 3.1 shows the various types of nitrogen fixation that occur throughout the world and gives estimates of the mass of atmospheric nitrogen fixed in a year. Table 3.1 type of nitrogen fixation mass of nitrogen fixed / ×109 kg yr–1 non-biological Haber process combustion lightning biological agricultural land non-agricultural land sea Using data from Table 3.1, calculate the percentage of nitrogen fixation carried out worldwide by nitrogen-fixing organisms, such as A. vinelandii, in agricultural land. Show your working and express your answer to the nearest whole number. answer % Explain why the proportion of nitrogen gas in the atmosphere remains stable at 78%, even though nitrogen fixation removes nitrogen gas from the atmosphere. Describe and explain the benefits to humans of the presence of nitrogen-fixing bacteria, such as A. vinelandii, in agricultural land.
9700_w11_qp_22
THEORY
2011
Paper 2, Variant 2
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shows the structure of the R groups of three amino acids, aspartate (Asp), glutamine (Gln) and isoleucine (Ile). C O– O CH2 Asp R group C NH3+ O CH2 CH2 GIn R group CH3 CH3 H CH2 C Ile R group One of the mRNA codons for the amino acid Gln is CAA. A mutation could change this codon from CAA to UAA. UAA is a STOP codon. State what is meant by a STOP codon. Many proteins that contain the amino acids shown in are globular. Describe how the three R groups in can contribute to the globular structure of a protein. An example of a globular protein is the enzyme starch phosphorylase. This enzyme catalyses the conversion of starch to glucose-1-phosphate. Name the type of bond that is broken when starch is converted to glucose-1-phosphate. An investigation was carried out to find out how the activity of starch phosphorylase varied with temperature, when free in solution and when immobilised in alginate. The results are shown in . temperature / °C enzyme activity / arbitrary units free enzyme immobilised enzyme Key With reference to , compare the results for the enzyme activity when free in solution and when immobilised. State how the Michaelis–Menten constant (Km) is derived from Vmax for an enzyme. The Km values for starch phosphorylase were determined when free in solution and when immobilised. The Km values were: • free in solution, Km = 0.34 mmol dm–3 • immobilised, Km = 0.84 mmol dm–3. Suggest an explanation for the difference between the two values.
9700_w17_qp_21
THEORY
2017
Paper 2, Variant 1
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Enzyme inhibitors and monoclonal antibodies can be used in the treatment of disease. Mevinolin is an enzyme inhibitor that can be prescribed as a drug to reduce the concentration of cholesterol in blood plasma. High concentrations of cholesterol in the blood have been linked to an increased risk of cardiovascular disease. Mevinolin acts as a competitive inhibitor of the enzyme HMG CoA reductase. This enzyme catalyses one of the first steps in the synthesis of cholesterol, as shown in . HMG CoA reductase HMG CoA mevalonic acid Explain how mevinolin inhibits the enzyme HMG CoA reductase. Outline the use of monoclonal antibodies in the treatment of disease.
9700_s18_qp_22
THEORY
2018
Paper 2, Variant 2
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A significant quantity of the metallic copper produced in some countries is obtained using the chemoautotrophic bacterium, Thiobacillus ferro-oxidans, which is present in rocks in many countries. The process, known as bioleaching, is shown in . Acidified water is pumped onto large heaps of waste material, containing iron and copper sulfides, left from conventional mining. Thiobacillus ferro-oxidans oxidises iron (sulfide to iron (sulfate. The iron (ions oxidise copper sulfide to soluble copper sulfate. The solution is collected in shallow ponds. step 1 step 2 step 3 step 4 Scrap iron is put into the ponds and the following reaction allows metallic copper to be precipated onto the iron: Cu2+ + Fe Cu + Fe2+ Metallic copper is scraped off the surface of the scrap iron and refined. Suggest the benefit to the bacterium of step 2. State two environmental disadvantages of extracting metals by bioleaching. 1. 2. Explain why the production of metallic copper by bioleaching can be cheaper than using conventional mining methods.
9700_s08_qp_4
THEORY
2008
Paper 4, Variant 0
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The fig tree, Ficus carica, and the papaya tree, Carica papaya, produce a milky-looking fluid known as latex. The latex is released when plant tissue is wounded and it is thought to act as a defence against attack by herbivorous insects or parasitic worms. Latex is a complex mixture of substances and the exact composition of the mixture depends on the plant species. A group of enzymes that hydrolyse proteins, known as cysteine proteases, are commonly found in latex. Ficin, found in F. carica, and papain, found in C. papaya, are both cysteine protease enzymes. These enzymes have been extracted and purified for use commercially. An investigation was carried out to compare the effect of temperature on the activity of ficin and papain. The results are shown in . temperature / °C percentage of maximum activity papain ficin With reference to , describe the differences between the activity of papain compared to the activity of ficin between 20 °C and 80 °C. Ficin and papain have been shown to be effective in the digestion of parasitic nematodes . With reference to , explain which enzyme you would select to use in an oral medication for the treatment of human intestinal parasitic nematodes. One commercial use of the enzyme ficin is the production of Fab fragments (antigen binding regions) of mouse IgG antibodies for use in immunological studies. The process uses immobilised ficin to cleave the antibodies in the hinge region. Suggest one practical advantage of using immobilised ficin for this process, rather than ficin free in solution. Streptococcus pyogenes is a bacterium that can cause a range of diseases in humans. S. pyogenes synthesises streptopain, a cysteine protease that hydrolyses structural proteins in human connective tissue. Streptopain is secreted to the outside of the cell. State the term given to an enzyme that is produced by a cell and is then secreted to the outside, where it has its action. Suggest one example of a structural protein in connective tissue that can be hydrolysed by streptopain.
9700_s18_qp_23
THEORY
2018
Paper 2, Variant 3
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In the small intestine, the enzyme lactase hydrolyses the disaccharide lactose into the monosaccharides glucose and galactose. A deficiency of lactase can lead to a condition known as lactose intolerance. The lactose passes undigested into the large intestine resulting in diarrhoea. Some babies are born with congenital lactase deficiency, which is an inherited condition, and require lactose-free milk from birth. Suggest how two parents, who can digest lactose, can have a child with congenital lactase deficiency. The enzyme lactase can be produced by biotechnology and then used to produce lactose-free dairy products. Lactase is frequently used immobilised in alginate beads. shows a comparison between the activity of lactase free in solution and lactase immobilised in alginate beads, over a range of temperatures. Equal concentrations of free lactase and immobilised lactase were used. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 temperature / ° C enzyme activity / arbitrary units Key free lactase immobilised lactase With reference to : describe the effect of immobilisation on the activity of lactase suggest explanations for the differences between the activity of immobilised lactase and free lactase up to 40 °C. State the advantages of using immobilised enzymes instead of free enzymes.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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Table 2.1 shows eight ions that are biologically important. Table 2.1 ammonium (NH4 +) A hydrogen (H+) B hydrogen carbonate (HCO3 –) C iron (Fe2+) D magnesium (Mg2+) E nitrate (NO3 –) F phosphate (PO4 3–) G sulfate (SO4 2–) H Choose one ion to match each of the following statements. In each case write one letter from Table 2.1. You may use each letter (A to H) once, more than once or not at all. A component of polynucleotides. Ion produced by enzyme activity inside red blood cells. Ion used in the production of all amino acids in chloroplasts. Ion that diffuses through carrier proteins with sucrose into companion cells in phloem tissue. Component of haem group in haemoglobin that binds oxygen. The enzyme nitrogenase is found in free-living and symbiotic nitrogen-fixing bacteria. Nitrogenase catalyses the reaction: N2 + 6 e– + 8H+ 2NH4 + Some nitrogenase enzymes have vanadium ions in their active sites; others have molybdenum ions. Explain how the enzyme nitrogenase functions in the fixation of nitrogen. Some pea plants were grown with their roots in a solution of mineral ions. The solution was kept aerated for three days. The concentrations of five ions in the solution and in the root tissue were determined after the three days. The results are shown in Table 2.2. Table 2.2 ion concentration / mmol dm–3 surrounding solution root tissue potassium (K+) 1.0 75.0 magnesium (Mg2+) 0.3 3.5 calcium (Ca2+) 1.0 2.0 phosphate (PO4 3–) 1.0 21.1 sulfate (SO4 2–) 0.3 19.7 With reference to Table 2.2, suggest how cell surface membranes of root cells are responsible for the concentrations of ions in the roots compared to the surrounding solution.
9700_w13_qp_21
THEORY
2013
Paper 2, Variant 1
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Questions Discovered
202