Enzymes Ex

1.
(a) In the figure above, what is the optimum pH for the activity enzyme B?

(b) Give an example of an enzyme which could be represented by
(i) activity curve A
(ii) activity curve B

(c) Why does the enzyme activity of C decrease at pH values between 8 and 9?

(d) Why is the control of pH important in vivo?

ANSWERS
1(a) pH 5.5
(b) (i) Pepsin (ii) Salivary amylase
(c) At pH values between 8-9 more and more enzymes start to denature as the pH increases above optimal (pH 7.5), therefore activity of enzyme decreases.
(d) ("In vivo" means in the body, opposite of "in vitro" which is outside the body) pH must be maintained for the fluids in the body (eg. plasma and tissue fluid), inside cells as well as in the organs, so as to ensure that the enzymes are working near their optimum pH and hence would catalyse reactions at a fast rate.

2. The experiment below was set up to investigate the action of the enzyme protease on gelatine (a protein). The gelatine contained a green dye that is released when the gelatine is broken down or ‘digested’.

(a) State a possible hypothesis that the experiment was investigating. [1]
(b) What is the variable in this experiment? [1]
(c) In which tube would you expect most green dye to be released? Why? [2]
(d) What is the purpose of test-tube A? [1]
(e) What results would you expect if the test-tubes were heated in a water bath of 75 0C? Why? [2]

ANSWERS
(a) An increased surface area to volume ratio increases the rate of protein digestion and hence the rate of release of green dye;(1m)

(b) The size of the gelatine pieces;(1m)

(c) B – protease is present to digest the gelatine;
The gelatine has an increase surface area to volume ratio which increases rate of digestion by protease, therefore the greatest amount of green dye will be released;(1mx2)

(d) A control, to which the other results can be compared, to show that the breakdown of gelatine (and release of green dye) is due to the action of protease;(1m)

(e) (Assuming that time is taken for tubes to heat up to water bath temp of 75 degrees Celsius)Some reaction would occur initially for tubes B and C, and green dye will be released, with a faster rate for tube B than C, while no green dye will be released in tube A;
After a short period of time, no more dye will be released from gelatine in B and C as the enzymes are denatured at high temperatures;(1mx2)