Testing for biological molecules Flashcards
What test would you use when testing for sugars?
Benedicts test (copper Cu2+ ions)
What test would you use when testing for starch?
Iodine solution
What test would you use when testing for protein?
Biuret reagent
What test would you use when testing for lipids?
Emulsion test (ethanol)
How do you perform the benedicts test for reducing sugars?
Add benedicts solution to the sample.
Heat the solution, don’t boil.
What colour will the benedicts test go after heating if there is low sugar concentration?
Green
What colour will the benedicts test go after heating if there is a high sugar concentration?
Brick red
What must be done before carrying out the benedicts test if testing for a non-reducing sugar?
The sugars must be broken down first.
Boil the solution with dilute hydrochloric acid.
Neutralise the acidic solution with sodium hydrogencarbonate.
What colour is a negative result for the iodine test for starch?
Browny-orange
What colour is a positive result for the iodine test for starch?
If starch is present the mixture turns blue-black.
What colour is a negative result when using the biuret reagent to test for protein?
Pale blue
What colour is a positive result when using the biuret reagent to test for protein?
If protein is present the mixture turns pale purple.
What is the method of the emulsion test?
Shake the sample with ethanol for 1 minute to dissolve any lipids.
Pour the mixture into water in a clean test tube.
What is a positive result for the emulsion test?
The solution will form a cloudy white emulsion (precipitate).
How can these colour-based tests be quantified?
Using colorimetry and a calibration curve created using a serial dilution of a known concentration.
