Biochemical Tests for Molecules

This is just loads of practicals involving biological molecules we need to know how to do.

Benedict's Test for Sugars
Sugar is a general term for Monosaccharides and Disaccharides. All sugars can be classed as Reducing or Non-Reducing. The Benedict's Test Differs depending on the Type of Sugar you are testing for.

BENEDICT'S TEST FOR REDUCING SUGARS

• Reducing sugars include All Monosaccharides (i.e. glucose) and some Disaccharides (i.e. maltose and lactose)
• To the sample, we need to add Benedict's Reagent (It's blue).
• now we need to heat it up and Bring it to the Boil. This is usually done in a Water Bath.
• The colour should go: BLUE>GREEN>YELLOW>ORANGE>BRICK-RED
• If the test is Positive, the Precipitate will Change Colour. The Higher the Concentration of reducing sugars, the Further the Colour Change will go.
• We can use this to compare the amount of reducing sugar in different solutions, however, weighing would be a more reliable alternative.

BENEDICT'S TEST FOR NON-REDUCING SUGARS

• If the result of the above test is negative, it could still have non-reducing sugars in the solution, such as sucrose. But first, we have to Break Them Down into Monosaccharides.
• For this, you will need a New Sample of the Test Solution.
• Add Dilute Hydrochloric Acid and Heat It in a water bath that has been Brought to the Boil.
• Then Add Sodium Hydrogencarbonate to neutralise the solution. Then carry out Benedict's test for Reducing Sugars as explained above. 
• If the solution forms a precipitate which is not blue, the solution contains non-reducing sugars.
• If the solution remains blue, there are no sugars present.

Test Strips for Glucose

Glucose can be tested for using Test Strips coated in a Reagent. The strips are Dipped in a Test Solution and Change Colour if Glucose is Present. The test strip can be Compared to a Chart to Estimate the Concentration of Glucose present. This is used in Urine Tests, which may indicate Diabetes.

Iodine Test for Starch

• Add iodine dissolved in Potassium Iodide solution to the test sample.
• If Starch is Present, the sample will change from brown/orange to Blue/Black.
• If there's no starch, the sample will stay brown/orange

Biuret Test for Proteins.

There are 2 stages:

1. The test solution must be alkaline, so we need to add a few drops of Sodium Hydroxide solution.
2. Then add Copper (II) Sulphate solution.

If Proteins are Present, the solution turns purple.

If no proteins are present, the solution will stay blue.

Emulsion Test for Lipids

• Add Ethanol to the Test Sample, and Shake Well for 60s.
• Then pour the solution into a test tube of Water.

If Lipids are Present, the solution will turn Milky.

If no lipids are present, the solution will remain clear.