chapter 4 II

Answers:

Objective questions

1. D	2. A	3. B	4. A	5. B
6. C	7. B	8. A	9. D	10.A

Activity 1

a- lock                    b-lock and key hypothesis           c- substrate

d-key            e-active site                               f-enzyme-substrate complex

g-enzyme     h-products

Activity 2

a) i)provide energy during respiration

   ii)as food storage

  iii)build cell walls of plant

b  i)respiration cannot occur

   ii)no storage food in the form of starch or glycogen

  iii)plant cells are irregular in shape because there is no cellulose

c)  To form the structure of cells such as protoplasm, connective tissues and

     muscles.

d)i)Plasma membrane is not well formed.

  ii)No absorption of vitamin A, D, E and K.

e) Biocatalysts-increase the rate of biochemical reaction.

f) i)No chemical reactions in the cells.

  ii)All lining processes stop functioning.

Activity 3

a) i) W: Fat molecule

        X: Lipase

        Y: Fatty Acid

        Z: Glycerol

    ii) X works on specific substrate molecules.

        X remains unchanged at the end of the reaction.

b) i) ‘Lock and Key’ hypothesis

    ii) In the ‘Lock and Key’ hypothesis of enzyme action, the substrate fits into the

        active site of the enzyme. Various types of bonds hold the substrate in the 

        active site to form an enzyme-substrate complex. The enzyme then

        converts the substrate to product. The product leaves the enzyme.

c) i)  Lipase are extensively used in the dairy industry for the hydrolysis of milk 

        fats.

    ii) Enzymes are named by adding the suffix –ase to the name of their

        substrate. For example; maltase catalyses the hydrolysis of maltose to

        glucose.

d) For most enzymes, denaturation occurs at about 60^oC. The high temperature

    breaks the bonds that forms the protein structure. The active site loses its

    shape and fails to fit the substrate.

Activity 4

a) The optimum pH for this enzymes is pH 6. The activity of the enzymes

    decreases at pH values of less and more than 6.

b) A change in the pH can alter the changes on the active sites and the surface

    of the substrate. This can reduce the ability of both molecules to bind with

    each other. Therefore, the reaction cannot take place.

c) i) This enzyme can remove lipid stains on clothes and function optimally at low

       temperature. This makes washing clothes easier as high temperatures are

       not required.

    ii) The value of pH that is too high or too low is corrosive and this can damage

        clothes and harm our hands.

   iii) The enzyme can disintegrate to form inorganic compounds which are not

        toxic to the environment.

Essay

Title: The effect of pH on activity of enzyme.

Problem statement: What is the effect of pH on the activity of the enzyme

                                pepsin?

Hypothesis: The enzyme pepsin is most active in an acidic medium.

Variables: a) Manipulated variable: pH for the medium

                 b) Responding variable: rate of the enzyme reaction (condition of

                     mixture-cloudy or clear)

                 c) Controlled variable: Temperature of the medium, volume of the egg

                     albumen solution

Apparatus and materials:

Thermometer, test tubes, water bath, dropper, egg albumen solution, distilled water, 1 % pepsin solution, 0.1 M hydrochloric acid, 0.1 M sodium bicarbonate solution, syringe.

Procedure:

1. The egg albumen solution is prepared by mixing the egg white from an egg 500ml of distilled water. The mixture is boiled and the big particles are removed.
2. With the help of a syringe, 2 ml of egg white solution is placed in the three test tubes and labelled P,Q and R.
3. The following solutions are then added into each test tube.(refer to the  figure below).

P: 1 ml of 0.1 M hydrochloric acid + 1 ml of 1 % pepsin solution

Q: 1 ml of distilled water + 1 ml of 1 % pepsin solution

R: 1 ml of 0.1 M sodium bicarbonate solution + 1 ml of 1 % pepsin solution

                              

4. A strip pf pH paper is placed inside each test tube and the pH of each

     solution is recorded.

5. The three test tubes are then placed in the water bath with its temperature 

           maintained at 37^oC for 15 minutes.

6. The condition of the mixture, whether cloudy or clear, is recorded.

Results:

Test tube	pH value	Beginning of experiment	End of experiment
P	3	cloudy	Clear (protein has been broken down)
Q	7	cloudy	Cloudy (protein remains)
R	8	cloudy	Cloudy (protein remains)

Conclusion:

 The hypothesis is accepted.

 The enzyme pepsin is most active in pH 3 which is an acidic medium. The

 enzyme pepsin requires pepsin an acidic medium to act on the protein