2.2 tests for bio molecules Flashcards
How do you test for starch?
Method: Add iodine solution
Colour change: If starch is present there will be a colour change from yellow-brown to blue-black
How do you test for reducing sugars?
Method: Heat a reducing sugar with benedicts solution.
Colour change: blue to orange
(goes blue to green to yellow to orange-red)
How do you test for Non-reducing sugars?
Method:
-Boil with hydrochloric acid to hydrolyse the sucrose in to glucose and fructose
-neutralise it using sodium hydrogencarbonate
-test for reducing sugars again
Colour change:
a positive result will be green, yellow, orange or red
How do you test for lipids?
Method: The emulsion test -mix the sample with ethanol (as lipids are not soluble in water) - filter -pour the solution into water
Colour change: A white emulsion indicates lipids
What is a reducing sugar?
A sugar which can ‘reduce’ other molecules by donating electrons.
e.g. the monosaccharides glucose, galactose, fructose
or the disaccharide lactose or maltose
Why do non-reducing sugars not show up using the method for reducing sugars?
They cant donate electrons, meaning they cant turn the Cu2+ into Cu+, so no copper oxide is formed.
Copper oxide is responsible for changing the colour.
What colour change shows a positive result for the test for sugars?
Start: Blue
End: Green -> Yellow -> Orange -> Red
(each colour shows an increase in the concentration of sugar)
What is the colour change when starch is present in iodine?
No Starch: Yellow brown
Starch Added: Blue-black
What is the name of the test for proteins?
Biuret Test
What colour change indicates the presence of protein in the biuret test?
Blue to Purple
How do we test for lipids?
Emulsion Test
Adding ethanol and water
What indicates a positive result from the emulsion test>
A cloudy white precipitate
