Proteins and Enzymes Exam Questions and Answers Already Passed
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Course
Proteins and Enzymes
Institution
Proteins And Enzymes
Proteins and Enzymes Exam Questions and Answers Already Passed
In an investigation, the rate at which phenol was broken down by the enzyme phenol oxidase was measured in solutions with different concentrations of phenol. The experiment was then repeated with a non-competitive inhibitor added to t...
Proteins and Enzymes Exam Questions and Answers Already Passed
In an investigation, the rate at which phenol was broken down by the enzyme phenol oxidase was
measured in solutions with different concentrations of phenol. The experiment was then repeated with
a non-competitive inhibitor added to the phenol solutions. The graph shows the results.
(a) Explain why an increase in concentration of phenol solution from 2.0 to 2.5 mmol dm-3has no effect
on the rate of the reaction without inhibitor. - Answers maximum rate at which enzyme can combine
with substrate / form enzyme-substrate complexes / substrate no longer limiting / enzyme is a limiting
factor;(active site of) enzyme saturated with substrate (disqualify active sites / enzymes 'used up');
Explain the effect of the non-competitive inhibitor. - Answers inhibitor attaches to enzyme away from
the active site;changes shape of active site and prevents formation of enzyme-substrate complex;
Calculate the percentage decrease in the maximum rate of the reaction when the inhibitor was added.
Show your working.
Draw a curve on the graph to show the results expected if a competitive inhibitor instead of a non-
competitive inhibitor had been used. - Answers curve below top curve (without inhibitor) joining to top
curve / continues to increase to end of x-axis(must not exceed or level out below 'without inhibitor
curve' and must start from origin);
Urease is an enzyme which hydrolyses urea to ammonia and carbon dioxide. The ammonia produces an
alkaline solution.
, In an experiment, a solution of urease was placed in tubing made from a partially permeable membrane.
This tubing was put into a large test tube containing urea solution, as shown in the diagram. A control
was set up with urease solution in the tubing and water outside.
After 5 minutes, samples were taken from inside and outside the tubing in each of the test tubes. The
samples were tested with an indicator that is yellow below pH 8.0 and blue above pH 8.0. The results are
shown in the table.
(a) Explain the result for tube A. - Answers urea diffused into / entered the tubing and was hydrolysed /
broken down (inside tubing);ammonia increases pH / makes (solution) more alkaline and indicator turns
blue as pH above 8 / due to alkalinity / due to ammonia;idea that outside stays yellow because urease
does not pass out;
The solutions inside and outside the tubing in tube B were tested after 30 minutes for the presence of
protein.
(i) Describe how the presence of protein in a sample of a solution could be detected. - Answers i) add
biuret solution / add sodium hydroxide + coppersulphate (solution);
(disqualify heat / boil, but accept warm)
violet / lilac / purple colour;
What results of the tests for protein would you expect for tube B? In each case explain your answer.
Inside the tubing;
Outside the tubing; - Answers (ii) inside: protein present, as enzyme is protein;outside: no protein, as
urease / enzyme / protein unable to passthrough membrane / out;
(accept correct result of biuret test as indicator of protein)
Describe how you would carry out an investigation to find the optimum temperature for the activity of
urease. - Answers method to maintain range of temperatures, e.g. water baths;method to measure rate
of activity - e.g. time taken to turn indicator blue;
In an investigation into carbohydrase activity, the contents from part of the gut of a small animal were
collected. The contents were added to starch solution at pH 7 and kept in a water bath at 25°C. At one-
minute intervals, samples were removed and added to different test tubes containing dilute iodine
solution. The colour intensity of each sample was determined. The graph shows the results.
(a) Explain the change in colour intensity. - Answers colour results from starch-iodine reaction;decrease
due to breakdown of starch by carbohydrase / enzyme;
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