Testing For Macromolecules

Carbohydrates that in solution contain an aldehyde group

-CHO

reducing sugars and non-reducing sugars

Used to test for presence of reducing sugars/simple carbohydrates Add reagent to solution and heat in a water bath.

copper (II) sulfate in an alkaline solution, BLUE color

if negative: solution remains BLUE if positive: solution gradually changes from BLUE to RED BROWN (copper (II) sulfate oxidizes to copper oxide due to reducing sugar)

If Benedict's Test was used and no change occurred, non-reducing sugars may be present. The disaccharide must first be broken down to two monosaccharides using hydrolysis. Add hydrochloric acid to the solution for the reaction to occur. Once reaction occurs, neutralize acid and perform Benedict's test once again. NOTE: BENEDICTS REAGENT NEEDS ALKALINE CONDITION TO WORK THEREFORE ACID MUST BE NEUTRALIZED

If a change occurs in the second test with Benedicts Reagent, then non-reducing sugars are present.

BG: Lugol's Reagent, or iodine solution, is used to test for the presence of starch. Starch's long coil structure has a hole through the middle that perfectly complements iodine molecules. To test, add drop of iodine solution into substance being tested.

Iodine solution is ORANGE-BROWN, if starch is present a BLUE-BLACK ppt will form

3 known tests 1) grease spot test 2) sudan red test 3) ethanol emulsion test !!!

Translucent grease spots on unglazed brown paper bags indicates presence of lipids (but not amount or location)

BG: Sudan red powder is a fat soluble dye. Simple add powder into solution and it will stain red where lipids are present

BG: Lipids do not dissolve in water but they do dissolve in ethanol. To perform this test, suspend sample into concentrated ethanol and shake vigorously, if lipids are present a cloudy white emulsion will form. If not, ethanol will simply mix with water and remain a clear solution.

Biuret Test

copper (II) sulfate and potassium hydroxide ( CuSO4 & KOH )

BG: All proteins have peptide bonds containing nitrogen atoms. These nitrogen atoms combine with copper (II) ions and form a PURPLE complex. Add biuret reagent to solution and wait a few minutes for color to gradually change. No heating required.

If long polypeptide chains are present, color will change from BLUE to PURPLE If short polypeptide chains are present, color will change from BLUE to PINK.

If long polypeptide chains are present, color will change from BLUE to PURPLE If short polypeptide chains are present, color will change from BLUE to PINK.