Question

Procedure:

1. 10 Test tubes were labelled (0C,0E,15C,15E,30C,30E,45C,45E,60C, and 60E.)

2. 2 mL cathecol-buffer at pH 6 was added into each test tubes.

3. 3.5 mL of water was added into all of the C tubes (0C,15C,30C,45C, and 60C.)

4. 3 mL of water was added into the remaining tubes.

5.The two tubes were put into an ice bath.

6. 0.5 mL of enzyme polyphenoloxidase was added into tube E when the mixture had reached certain T (O°C)

7.The transmittance of both C and E test tubes were measured using spectrophotometer no sooner had the mixture been well-mixed.

8.The experiment was repeated as the procedure written in number 5-8, but the temperature was changed into "15C" and "15E"

9. The experiment was repeated for the remaining temperatures as the procedure written in number 5-8, except for number 6: The tubes were put into the water (hot) bath.

Questions (I will be quizzed on.)

1.What is the optimum Temperature according to your data?

2.Explain what causes the changes in reaction rate in the 0°c tubes as compared with tubes at high temperatures, up to the optimum temperature.

3.After passing the optimum temperature, why does further increase in temperature cause a decrease in the reaction time?

Tube # % Transmittance

OC 100%

0E 37.2%

15C 100%

15E 15.1%

30C 100%

3OE 15%

45C 100%

45E 21.3%

60C 100%

60E 33%

Please answer questions 1-3, explain, thank you.

Answer 1

Ans.1. % transmittance of all controls is 100% and that of respective enzyme-treatments at various temperatures are less than 100%. It means that % transmittance of the sample is inversely proportional to the concentration of end-product (a chromophore, that absorbs light at specific wavelength of the protocol).

Therefore, greater is % transmittance, lesser is the rate of reaction at the specified temperature.

Thus, the order of rate of reaction is-

            r (15 E) = r (30 E) > r (60E) > r (0E) ; where, r= rate of reaction.

Since, the maximum reaction rates are obtained at both 15⁰C and 30⁰C, both represent the optimum activities. The optimum temperature is, therefore, 15-30⁰C.

Ans. 3. Like chemical reactions, the enzyme-catalyzed reactions also involve enzyme-substrate collision in correct orientation. Greater the fruitful collisions, greater is the rate of reaction

Increase in temperature increases the kinetic temperature of the enzyme and substrate molecules as well as the molecules constituting the reaction medium. Increase in kinetic energy of enzyme and reactant molecules also increase the rate of collision i.e. greater number of substrate molecules are expected to collide with the enzyme per unit time.

Therefore, increase in kinetic energy of the substrate and enzyme at higher temperature increases the rate of reaction. Increase in rate of the reaction of a reaction (enzyme catalyzed or a simple chemical reaction) catalyze greater number or substrate per unit time and thus, the reaction time is decreased.

For example, a reaction at 10⁰C forms 100 molecules of products per second- it will take 10 seconds to from 1000 molecules of product. The same reaction forms 200 products at 20⁰C per seconds - it will take only 5 seconds to from 1000 molecules of product. Thus, at 20⁰C, the rate of reaction is increased and the reaction time is decreased.