1: Enzyme concentration affecting the initial rate of reaction

Question 1

Independent variable

Answer 1

Enzyme concentration (trypsin)

Question 2

Dependent variable

Answer 2

change in absorbance per second (rate of reaction)

Question 3

What are the factors that affect enzyme activity (4)?

(these 4 factors need controlling)

Answer 3

1. Enzyme concentration
2. Substrate concentration
3. Temperature
4. pH

Question 4

How is a control set up in a practical measuring enzyme activity?

Answer 4

Replace the enzyme solution with distilled water or boiled enzyme solution.

Question 5

Name the substrate found in milk

Answer 5

casein

Question 6

What device is used to measure change in absorbance?

Answer 6

colorimeter

Question 7

Over time the solution changes colour from white to _____

Answer 7

colourless

Question 8

Why are comparisons made at the start of a reaction?

Answer 8

There are no limiting factors,

substrate concentration is at its highest and their concentration values are known and thus can be compared

Question 9

If the cuvette used for the reaction was scratched (but the reference cuvette wasn’t) would this give a systematic error or random error?

Answer 9

Systematic error because
it would cause absorbance readings to be higher than the true value for every measurement

Question 10

How can the results of the practical measuring enzyme activity be used to find the initial rate of reaction?

Answer 10

Plot your results on a graph of ‘rate of reaction’ against ‘time’.
Draw a tangent at time = 0 to find the initial rate.

Question 11

Outline the practical procedure used to measure the effect of temperature on enzyme activity, using trypsin and milk.

Answer 11

Immerse equal volumes of trypsin and milk, stored in different test tubes, in a water-bath for 5 minutes for the temperature to equilibrate.
Mix together and immediately start timing, record the time taken for the milk to be completely hydrolysed (become colourless/ same as the control standard set up).
Test at least 5 temperatures, with at least 3 repeats at each temperature.

Question 12

How is the rate of reaction calculated from time?

Answer 12

Rate of reaction = 1/time

Question 13

What is the effect of temperature on enzyme activity?

Answer 13

As temperature increases, kinetic energy increases so more ES complexes form. The rate of reaction increases up to the optimum temperature.
Beyond that, bonds in the enzyme tertiary structure break, which changes the shape of the active site. The substrate and enzyme are no longer complementary, so rate of reaction decreases.

Question 14

What is the risk and level of risk associated with handling enzymes?

Answer 14

Students may have allergic reactions to enzymes, so avoid contact with skin and eyes, wear eye protection.
Low risk.