Required Practical 1 - Temperature & Rates of Reaction

Question 1

What is casein?

Answer 1

A protein found in milk. It causes it to be white & opaque

Question 2

What s trypsin?

Answer 2

The enzyme that digests casein

Question 3

How did you measure the volumes of trypsin, pH7 buffer solution and milk solution? Why not measuring cylinders?

Answer 3

Resolution on measuring cylinders too low
Used 3 separate pipettes to avoid contamination, as didn’t want experiment to start yet.
Needed 10cm cubed of all, so filled the 5 cm cubed pipette twice

Question 4

How did you alter the temperature of the solutions?

Answer 4

With a water bath, as a bunsen burner is unable to sustain a steady temperature

Question 5

Why did you add pH 7 buffer solution to trypsin?

Answer 5

When a protein (casein) breaks down, becomes amino acids. Would alter pH of the solution when product builds up, closer to pH 1. Altering pH can affect the rate of reaction, as it breaks ionic bonds formed in tertiary structure of making a protein/ enzyme. Causes protein to unfold, so enzyme denatures & slows down rate of reaction. pH is a control variable, so must be maintained with the buffer solution no matter how much acidic product is formed.
Also, buffer solution won’t chemically alter trypsin, so doesn’t matter if they’re together

Question 6

Why do we put both test tubes in the water bath for 10 minutes before mixing them?

Answer 6

Takes a while to reach the right temperature.
If only one test tube in water bath, then mixed with different temperature test tube, new solution would suddenly drop to an unknown temperature between the 2. Makes the experiment unfair/ not repeatable

Question 7

Why is it important to put the test tube back into the water bath after mixing trypsin and the milk solution?

Answer 7

Without the water bath, test tube would gradually decrease in temp until it reaches room temperature. The independent variable wouldn’t be controlled, so results not repeatable

Question 8

Why does the milk solution change from white & opaque - clear?

Answer 8

The protein casein in the milk causes the milk to be white & opaque. Once trypsin starts breaking down casein into amino acids, that property fades with casein, so it becomes colourless.
The reaction is complete when it is completely colourless - why reaction is times with the cross becoming visable

Question 9

What did you measure in seconds?

Answer 9

How long it took for the cross to become visable