YEAR 2 : Practical 1 - Invesigation of dehydrogenase activity In yeast

Question 1

What is yeast?

Answer 1

A single celled living organism

Question 2

Which processes is the enzyme dehydrogenase involved in?

Answer 2

Glycolysis
The link reaction
Krebs’ cycle

Question 3

Where does yeast perform aerobic respiration?

Answer 3

Where there is access to oxygen, towards the top of a suspension in a test tube

Question 4

Where does yeast perform anaerobic respiration?

Answer 4

Lower down in a test tube where there isn’t access to oxygen

Question 5

What does the enzyme dehydrogenase’s activity do?

Answer 5

Removes hydrogen atoms from intermediates in both types of respiration and transfers them to hydrogen acceptors like NAD

Question 6

How is a colour change brought on in this practical?

Answer 6

If an artificial hydrogen acceptor is added to the suspension, it will accept the hydrogen atoms and undergo a colour change on being reduced

Question 7

How do we measure the rate of dehydrogenase’s activity during this practical?

Answer 7

The time taken for the artificial indicator to change colour can be used as a measure of the rate of dehydrogenase activity

Question 8

Apparatus of the experiment

Answer 8

Redox indicator ; methylene blue
Yeast suspension
Water baths
Test tubes
Cork for test tubes
10cm^3 syringe
1cm^3 syringe
Stop clock

Question 9

Amount of methylene blue

Answer 9

0.05g/100cm^3

Question 10

Amount of yeast suspension

Answer 10

100g/dm^3

Question 11

Method of this practical

Answer 11

1.) Place 10cm^3 of the yeast suspension into a test tube
2.) Place test tube in water bath for 5 minutes to equilibrate
3.) Add 1cm^3 methylene blue indicator
4.) Place a cork on top of the test tube and invert once to mix
5.) Replace the test-tube in the water bath
6.) Time how long the indicator takes to change colour

Question 12

What is the colour change that occurs?

Answer 12

From blue to creamy

Question 13

Why does the colour change occur?

Answer 13

As yeast respires, dehydrogenase reduces methylene blue until it loses its colour

Question 14

How do we alter the method in order to measure the effect of temperature on the activity of dehydrogenase?

Answer 14

Use 5 different temperatures —> room temperature and set the water baths to 4 other temperatures

Question 15

What does a higher temperature cause?

Answer 15

Faster colour change

Question 16

Why does a higher temperature water bath result in a faster colour change?

Answer 16

More collisions due to higher kinetic energy of enzymes = increased probability of substrates colliding with the enzyme’s active site

Question 17

What must we do as yeast is in suspension?

Answer 17

Ensure to mix it so that it isn’t stronger at the bottom

Question 18

What’s the biggest fault in this practical?

Answer 18

The colour change is subjective

Question 19

What can we do to resolve the issue of the colour change being subjective?

Answer 19

Use a colorimeter or colour chart for better accuracy