enzymes exam questions

Question 1

what is an enzyme? (2)

Answer 1

-protein
-catalyst

Question 2

Gelatine is a protein. When a warm gelatine solution cools, it sets to form a jelly.
Fresh pineapple juice contains an enzyme that digests protein.
A student investigated the effect of pineapple juice on the setting of jelly.
He set up three different tubes of warm gelatine solution and recorded which had set after three hours. The contents of each tube and his results are shown in the table.

Tube Contents of tube Jelly formed
A 6 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 water No
B 6 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 hydrochloric acid Yes
C 6 cm3 gelatine + 2 cm3 boiled pineapple juice + 2 cm3 water Yes
(a) Explain why 2 cm3 of water was added to tubes A and C.

(2)

Answer 2

-to keep concentration of gelatine constant
-to keep concentration of pineapple juice constant.

Question 3

explain the results for tube A and tube B

Answer 3

tube A- enzyme in pineapple juice digests protein in gelatine
so no gelatine to form jelly

Tube B- enzyme in juice is denatured
-by hydrochloric acid
-tertiary structure changes

Question 4

what was the purpose of tube C

Answer 4

-to act as a control
-shows that enzyme in pineapple breaks down gelatine
-boiling denatures enzyme

Question 5

A student investigated the effect of lipase concentration on the hydrolysis of lipids.
He took a beaker containing a suspension of lipids. He placed a pH probe attached to a data logger into the beaker. After 5 minutes, he added the lipase solution. The data logger recorded the pH. The apparatus used is shown in the diagram below.

(a) The student did not add a buffer to the lipase solution.
Explain why.
(1)

Answer 5

-student is measuring the change in pH

Question 6

give 2 variables the student would have controlled in this investigation. (2)

Answer 6

-temperature
-volume of lipase solution.

Question 7

give the suitable control for this investigation. (1)

Answer 7

-boiled lipase solution

Question 8

explain the results shown in the graph (2)

Answer 8

-fatty acids produced
-curve levels off as all substrate used up.

Question 9

) The student repeated the experiment with a higher concentration of lipase solution.
Describe and explain the results you would expect him to get.
(3)

Answer 9

-faster fall in pH and levels off at same point
-more enzyme substrate complexes formed
-same amount of fatty acids produced

Question 10

describe the induced fit model of enzyme action. (2)

Answer 10

-shape of active site changes shape as enazyme substarte complex forms
-stressing/bending bonds in substrate.

Question 11

) A scientist investigated the hydrolysis of starch.
He added amylase to a suspension of starch and measured the concentration of maltose in the reaction mixture at regular intervals.
His results are shown in the graph below.

explain the results shown in the graph. (2)

Answer 11

-increase in concentration of maltose slows as starch is used up

Question 12

In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature.
Explain why maltase:
* only breaks down maltose
* allows this reaction to take place at normal body temperature.
(5)

Answer 12

-tertiary structure of enzyme
-means active site is complimentary to maltose
-active site changes shape slightly to mould around substrate/induced fit model
-enzyme acts as a catalyst/lowers activation energy
-as enzyme substrate complex forms.