Practical Biochemistry 2: Quantitative Tests for Biological Molecules

Question 1

When testing for reducing sugars, what happens if there’s more sugar present?

Answer 1

• Precipitate amount will increase
• Copper (II) ion amount remaining in solution will decrease

Question 2

How can we try to quantify the concentration of sugar in the original sample?

Answer 2

Assessing how precipitate and copper ion amounts change, using colorimetry

Question 3

How does a colorimeter work?

Answer 3

Shining a light through sample, using a centrifuge to separate precipitate and excess Benedict’s solution (supernatant)

Question 4

What is a supernatant?

Answer 4

Usually clear liquid lying above sediment, precipitate, or solid material settled at container bottom, often after process like settling, precipitation, or centrifugation

Question 5

What is a cuvette?

Answer 5

A small vial

Question 6

How can we use a colorimeter?

Answer 6

1. Use a pipette to take supernatant and place it in cuvette
2. Place into colorimeter, ensuring not to leave greasy fingerprint on cuvette surface
3. Using filter, shine coloured light through solution, detecting how much passes through (percentage transmission)

Question 7

What is a cuvette commonly made from?

Answer 7

Glass or plastic

Question 8

Why is it important not to leave a greasy fingerprint on the cuvette?

Answer 8

It could affect light transmission

Question 9

Why are coloured filters often used in colorimetry?

Answer 9

For greater accuracy

Question 10

In colorimetry, what colour does the solution reflect and absorb?

Answer 10

• Reflects blue light
• Absorbs red light

Question 11

In colorimetry, why does the solution absorb red light?

Answer 11

If there’s lots of unreacted copper sulfate, supernatant is still quite blue, absorption of red light is high and percentage transmission is low

Question 12

In colorimetry, why does the solution reflect blue light?

Answer 12

If there’s little unreacted copper sulfate, supernatant is less blue, absorption of red light is low and percentage transmission is high

Question 13

How can a colorimeter be zeroed between readings?

Answer 13

Placing appropriate ‘blank’ sample to reset 100% transmission/absorption, can be water

Question 14

How is a calibration curve used?

Answer 14

1. Take series of known concentrations of reducing sugar
2. Using sample of each, carry out Benedict’s test
3. Use colorimeter to record percentage transmission of light through
4. Plot graph to show ‘transmission of light’ against concentration of reducing sugar

Question 15

What can a calibration curve be used to find out?

Answer 15

Used with other ‘unknown’ samples to determine concentration of sugar in original sample

Question 16

How does a biosensor work?

Answer 16

Take biological or chemical variable cannot easily be measured and convert it to an electrical signal

Question 17

When colorimeters use UV light, what do cuvettes need to be made of?

Answer 17

Quartz

Question 18

What does a biosensor look like?

Answer 18

Question 19

What can biosensors be used to detect?

Answer 19

• Contaminants in water
• Pathogens/toxins in food
• Airborne bacteria