Topic 4: Enzymes and metabolism

Transcription

1 Topic 4: Enzymes and metabolism 1. An is a living molecule produced by glands to digest food in the alimentary canal. living molecule produced by cells to synthesise complex molecules from simpler ones. protein molecule produced by living cells to catalyse a particular biochemical reaction. protein molecule produced by living cells to catalyse a particular biochemical reaction at 37oC 2. An is only required in a small amount because its shape is specific. it speeds up both forward and backward reactions. it is made of proteins. it is not consumed in the reaction. 3. Which of the following can cause denaturation of s? high temperature low temperature presence of a competitive inhibitor only and only and only, and 4. Enzymes can be denatured by heat because they Need optimal temperature to work Are active in cold only Are structurally changed in high temperature Are biological catalysts 5. Which statement is true for all s? They are denatured at Temperature above 60 They catalyse the breakdown of larger molecules into smaller one They have active sites which can bind to only one kind of molecule They reduce the amount of energy required to start a reaction. 6. Life is maintained by metabolism which refers to all Breaking down reactions in the cells Building up reactions in the cells Essential biochemical reactions in the cells Food oxidation and energy releasing processes in the cells 7. Which of the following cannot increase metabolic rate? eading Sleeping Talking

2 Jogging 8. Which property of s can be explained by the lock-and-key hypothesis? Enzymes are reusable. Enzymes are proteins. The actions of s are specific. Enzymes are biological catalysts. Directions: uestions 9 to 11 refer to the diagram below, which shows the molecules before and after an enzymatic reaction: Before reaction After reaction T S 9. What are molecules to T? S T A product B product C product D product product 10. Which of the following statements is/are correct? The specificity of the action of can be explained by the lock-and-key hypothesis. and represent the lock in the lock-and-key hypothesis., S and T represent the key in the lock-and-key hypothesis. only and only and only, and 11. The reaction is an example of metabolism. catabolism. anabolism. and only and only and only

3 , and 12. Which of the following are examples of catabolism? amino acid --> protein glucose --> water + carbon dioxide lipid --> glycerol + fatty acid and only and only and only, and 13. Amylase is an which catalyses the breakdown of starch to sugar. However, it cannot catalyse the breakdown of cellulose. This is because amylase is denatured by cellulose. amylase can only work in a narrow range of ph. amylase has a specific active site. cellulose is an inhibitor to the action of amylase. 14. Which of the following is/are possible (s) for X? X active sites only and only and only, and 15. In an investigation of the effect of temperature on the activity, four test tubes containing an solution and some milk were kept in water baths of different temperatures. The time taken for the milk to coagulate was recorded. The results are shown in the table below. Temperature of water bath ( C) Time taken for coagulation of milk (min) X

4 X denotes no coagulation after 30 minutes. What can be concluded from the results? The activity of this is affected by temperature. The optimum temperature for this is 40 This is denatured at high temperatures. A only B only C and only D, and Directions: uestions 16 to 18 refer to the diagram below which shows an experiment. Equal volumes of amylase solution were added to each of the four test tubes. All the tubes were kept at 40oC and the contents were maintained at ph 7. amylase added to each tube At the beginning W After 30 minutes W X Y X cloudy egg white suspension clear sucrose solution cloudy starch suspension cloudy egg white suspension Z Y clear maltose solution clear cooking oil Z clear sucrose solution clear cooking oil 16. Which of the following is the factor being investigated? ph temperature 17. Which of the following is the conclusion of this experiment? Amylase works best at 40o Amylase can digest all the food substances except egg white. Amylase is specific to its. Amylase works best at ph If lipase were used instead of amylase, which tube would contain acidic contents after 30 minutes? W X Y Z 19. Seeds produce some s when they germinate. Which of the following is the main function of these s? to synthesise starch from sugars for storage

5 to increase the rate of water absorption in the root to break down insoluble food into soluble forms to carry out photosynthesis 20. When hydrogen peroxide solution is added to a wound for sterilization, bubbles evolve rapidly from the wound. Which of the following is a correct explanation of the phenomenon? The red blood cells contains catalase The haemoglobin liberates oxygen. The hydrogen peroxide increases the respiratory rate of the wounded tissues. Carbon dioxide is evolved from the wounded tissue. Directions: uestions refer to the diagram below, which is a diagrammatic representation of an catalysed reaction. S S 21. Which of the following substances can be used again? S 22. Which of the following statement can be deduced from the diagram? Enzyme action is specific. The reaction is reversible. Enzymes are inactive at low temperatures. and only and only and only, and 23. Which of the following is not explained by the diagram? Enzymes can be reused. Enzymes is specific Enzymes reaction is reversible eaction rate is speeded up. 24. Which of the following enzymatic reactions can be represented by the diagram? Formation of fat

6 formation of lactose Formation of sucrose Formation of protein 25. What would happen when an with an optimum ph of 8.5 is added to a solution with a ph of 4? The may be denatured. The activity would be lower at ph 4 than ph 8.5. The activity would be the same at both ph values. only and only and only and only 26. A fresh potato was mashed and some extract of the mash was added to a starch solution. After 20 minutes, a r educing sugar was detected in the mixture. Which of the following control experiment(s) is (are) required to conclude that the extract contained an that digest starch? Boil the extract before adding it into the starch solution Use water instead of extract The extract had to be tested with Benedict s solution Only and only and only, and Directions: uestions below refer to the apparatus below which is used to compare the activities of the catalase extracted from different tissues. The action of catalase is as follow:

7 27. What are, and at the beginning of the experiment H2O2 H2O2 catalase H2O2 H2O catalase catalase H2O H2O2 H2O2 H2O catalyse 28. How can the reaction rate be measured? Measure the amount of gas collected in the first 30 seconds Measure the amount of gas collected when the reaction has completed. Measure the amount of H2O2 left in the flask. Measure the amount of water formed in the flask. 29. Which of the following is not a precaution of the experiment? All joints must be air-tight The amount of extracted added each time must be the same/ The amount of H2O2 used each time must be the same. The tap must be kept open during experiment. ate of reaction Directions: uestions 30 and 31 refer to the graph below which shows the rate of reactions catalysed by s X, Y and Z over a range of ph values. Z Y X The rates of the reactions catalysed by s X and Y are equal at ph 4. ph 5.5. ph 6.5. ph Which of the following is the most probable conclusion that can be drawn from the graph? The optimum ph values for s X, Y and Z are 4, 7 and 8.5 respectively. Enzyme X is found in the stomach and Y is found in the mouth. Enzyme Z is more active than X and Y. only and only and only, and

8 Directions: uestion below refer to the following experiment which investigates the activities of the catalase which can be found in the liver of man. It catalyses the following reaction: catalase Hydrogen peroxide water + oxygen Catalase was added to 5cm3 hydrogen peroxide solution and the oxygen evolved in the first minute was collected. The results are shown below. Test tube Temperature( ) Volume of oxygen collected(cm3) S What conclusions can be drawn from the above results? The s was destroyed at low and high temperatures. For every 10 increase in temperature, the reaction rate was double. The only worked at certain temperature range. eaction rate varied linearly with temperature. 33. If another temperature is to be tested, which temperature should be chosen to get the maximum amount of oxygen? If test tubes and S were them immersed in a water bath of 20, what would be the amount of oxygen collected in the first minute? S 0 cm3 0 cm3 0 cm3 10 cm3 10 cm3 0 cm3 10 cm3 10 cm3

9 35. Experiments were carried out using the apparatus below. rubber cap oxygen hydrogen peroxide solution potato disc In which of the following conditions was oxygen produced most rapidly? Number of potato discs Condition of potato discs 5 boiled 10 boiled 5 raw 10 raw activity concentration concentration activity activity activity 36. Which of the following graphs shows the effect of concentration on activity? concentration concentration 37. Which of the following can reduce the effect of a competitive inhibitor on s? increasing the concentration adding another non-competitive inhibitor decreasing the temperature at which the reaction takes place only and only and only, and

10 38. Which of the following statements about inhibitors is correct? Cyanide and copper(ii) ions are competitive inhibitors. Competitive inhibitors alter the structure of s. Enzymatic activities cannot be restored by increasing concentration in the presence of noncompetitive inhibitors. All inhibitors have a similar shape with the molecules. Directions: uestions refer to the following diagram, which shows a reaction involving X and s ubstrate. Molecules were then added. The figures in the diagram show their quantity in relative units. 39. If and has similar affinity to X, which of the following would occur when 200 units of molecule were added to the reaction involving X and? The rate of reaction would increase by 20%. The rate of reaction would decrease by 20%. The would stop its activities. The rate of reaction would not be affected. 40. If 2000 units of molecule were added to the reaction instead of molecule, which of the following would occur? The rate of reaction will increase. The rate of reaction would increase sharply. Molecules would block most of the s. The rate of reaction would not be affected. 41. If molecules had not been added to the reaction, what should be the quanitities of the and after the reaction has been completed? Enzyme X Substrate 0 unit 0 unit 100 units 100units 100 unit 0 unit 0 unit 900 units

11 42. An experiment was carried out to investigate the effects of two metals on activities. An and its were incubated at 40oC with various concentrations of either metal X or metal Y. The time taken for the complete breakdown of the was measured. The results were recorded in the table below. Concentration (ppm) Time needed to break down the (seconds) Metal X Metal Y (ppm = parts per million) Which of the following correctly describes the effects of high concentration of these metals on activity? High concentration of metal X inhibited inhibited promoted promoted High concentration of metal Y promoted inhibited inhibited promoted ate of reaction 43. The graph below shows the reaction rate of an without inhibition and that of the same in the presence of an inhibitor. Which curve represents the effect of a non-competitive inhibitor? no inhibition (4) Substrate concentration (4) 44. In an investigation to determine the effect of temperature on the activity of an, the time for all the to disappear from a standard solution was recorded. Which graph shows the results of this investigation?

12 45. In the following graph, each of the curves, and represents an -controlled reaction in one of the following situations: - With the uninhibited - With a non-competitive inhibitor added to the - With a competitive inhibitor added to the Which curve represents each situation? Uninhibited competitive added non-competitive added Directions: uestions 46 to 47 refer to the experiment below. TEST 1: 1 g of freshly ground liver was placed in a test tube with 1 cm3 of hydrogen peroxide. A gas was formed. The gas re-lit a glowing splint TEST 2: 1 g of ground liver was boiled. When fresh hydrogen peroxide was added to the boiled liver, no gas was formed. TEST 3: Ground liver treated with strong acid produced results similar to those obtained in test 2. TEST 4: Ground liver treated with strong alkali produced results similar to those obtained in test 2.

13 46. A hypothesis about activity in liver is being tested. The hypothesis is that the activity is affected by acids, alkalis, boiling and hydrogen peroxide. acids, alkalis and hydrogen peroxide. acids, alkalis and boiling. grinding the liver. 47. Which of the following test tubes was the control for the experiment? the one containing boiled liver and hydrogen peroxide the one containing freshly ground liver and hydrogen peroxide the one containing liver treated with alkali the one containing liver treated with acid 48. Which test(s) showed that the reaction was controlled by an? test 1 only test 1 and test 2 only test 2, test 3 and test 4 only test 1, test 2, test 3 and test 4 Directions: The following two questions refer to the diagrams below, which show the set-ups for investigating the effectiveness of washing powders on stain removal. protein stain lipid stain cloth cloth o Non-biological powder at 25 C Non-biological powder at 25 C (4) o protein stain protein stain cloth cloth o o Biological powder at 25 C Biological powder at 35 C 49. Which two set-ups are compared to show the effect of temperature on stain removal? A and B and C and (4) D and (4) 50. Which factor is being investigated by comparing and? A temperature B type of washing powder C type of cloth D type of stain 51. Which of the following is/are the advantage(s) of using s in industrial processes?

14 Can reduce the production of unwanted products Only small amount is required Can work well in low temperature (4) Does not need extreme and expensive conditions such as very high temperature or pressure. and, and, (4), and (4) 52. How can s help in manufacturing sofa? Making it tougher by digesting fibre emove hairs from hides (牛皮) Making the color of the sofa Make it more spongy