Biological Molecules - Enzyme-Controlled Reactions

Question 1

How do you
MEASURE the RATE of an ENZYME-CONTROLLED REACTION

by
measuring HOW FAST the PRODUCT is made?

Answer 1

• Set up boiling tubes containing the same volume and concentration of hydrogen peroxide.

To keep pH constant, add equal volumes of a suitable buffer solution to each tube.

• Set up the rest of the apparatus:
  i. e. bung in boiling tube and delivery tube from boiling tube to upside down measuring cylinder in trough of water.
• Put each boiling tube in a water bath set to a different temperature
  (e.g. 10 degrees, 20, 30, 40)
  along with another tube containing catalase

(wait 5 mins before moving onto the next step so the enzyme gets up to temperature)

• Use a pipette to add the same volume and concentration of catalase to each boiling tube. Then quickly attach the bung and delivery tube.
• Record how much oxygen is produced in the first minute (60s) of the reaction. Use a stopwatch to measure the time.
• Repeat the experiment at each temperature three times, and use the results to find an average volume of oxygen produced.
• Calculate the average rate of reaction at each temperature by dividing the volume of oxygen produced by the time taken (i.e. 60s). The units will be cm3s-1.
  ___________________________________

NOTE:

Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen.
It’s easy to measure the volume of oxygen produced and to work out how fast it’s given off.
The oxygen displaces the water from the measuring cylinder. (a clamp stand would also be pretty useful to hold the cylinder upside down, as would a stopwatch and a water bath.)

Question 2

How do you
MEASURE the RATE of an ENZYME-CONTROLLED REACTION

by
measuring HOW FAST the SUBSTRATE is BROKEN DOWN?

Answer 2

The enzyme AMYLASE catalyses the breakdown of STARCH to MALTOSE.

A drop of iodine in potassium iodide is put into each well on a spotting tile.

A known concentration of amylase and starch are then mixed together in a test tube.

A dropping pipette is used to put a drop of this mixture into one of the wells containing the iodine solution on the spotting tile at regular intervals and the resulting colour is observed.

The iodine solution goes DARKER BLUE-BLACK when STARCH IS PRESENT but remains its normal BROWNY-ORANGE colour when there’s NO STARCH around.

You can see how fast amylase is working by recording how long it takes for the iodine solution to no longer turn blue-black when starch / amylase mixture is added.

Repeat the experiment using different concentration of amylase.

Make sure that you also repeat the experiment three times at each amylase concentration.