Tests For Biological Molecules Flashcards
What is the name of the test for sugars
Benedict’s test
What does the term sugar mean
Term for monosaccharide and disaccharide
Test for reducting sugars
Add Benedict’s reagent to sample heat it in water bath that’s been brought to boil.
If test is positive it will form a coloured precipitate.
Higher the concentration of reducing sugar the further the colour change goes.
What sugars are reducing sugars
All monosaccharides and some disaccharides like lactose and maltose.
What is a coloured precipitate
Solid particles suspended in solution
What’s an accurate way of comparing how much reducing sugar is in different solutions.
Filter the solution and weigh the precipitate.
Test for non reducing sugars
If result of reducing sugars is negative there could be a non reducing sugar present.
To test for a non reducing sugar you first have to break them down into monosaccharides.
You do this by adding dilute hydrochloric acid and heat sample in water bath brought to boil. Then you neutralise substance with sodium hydrocarbonate. And carry out Benedict’s test.
Give an example of a non reducing sugar
Sucrose.
How do you test for starch?
You use iodine.
Test for starch
Add iodine dissolved in potassium iodide solution.
If starch present browny orange to blue black.
No starch stays browny orange.
What test do you use for proteins
Biuret test
How do you do a biuret test
The test solution needs to be alkaline, so first add a few drops of sodium hydroxide solution.
Then add copper 2 sulfate solution.
Results for biuret test
If protein present solution turns purple
Negative stays blue
What test do you use for lipids
You use the emulsion test
How do you carry out the emulsion test?
Shake test substance with ethanol for 1 minute. Then pour into water.
If lipid present solution turns milky.
The more lipid the more noticable the colour change. If no lipid stays clear.q
