Question

Which one of the following is not a test for sugar?

• A. Benedict's test \
• B. Fehling's test \
• C. Bradford test \
• D. Molisch test

Hint:

Bradford = Blue = Protein! It is one of the most common protein-binding assays used in biological research labs around the world.

Answer 1

The Correct Option is C

Step 1: Concept Specific diagnostic biochemical color tests are designed to distinguish between fundamental biomolecule classes, such as carbohydrates (sugars) and proteins.

Step 2: Meaning * Sugar assays generally monitor condensation reactions with phenols or the reduction of alkaline heavy metal solutions. * Protein assays monitor complexation or binding interactions with unique dyes or metallic ions.

Step 3: Analysis * Benedict's test (A): Detects reducing sugars through copper reduction. * Fehling's test (B): A classic test used to differentiate between water-soluble carbohydrate aldehydes and ketones. * Bradford test (C): A colorimetric protein assay based on an absorbance shift of Coomassie Brilliant Blue G-250 dye when it binds to basic and aromatic amino acid residues. It has zero reactivity with sugars. * Molisch test (D): A general test for all carbohydrates based on acid dehydration to furfural derivatives which condense with $\alpha$-naphthol to form a purple ring.

Step 4: Conclusion Therefore, the Bradford test is strictly a protein assay and is not used for carbohydrate or sugar identification. Final Answer: (C)