This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Intact peptide bond is necessary for which test 
Select and explain. 
A. UV diffraction, B. Ninhydrin, C. Diazo reaction, D. All
A: UV diffraction
Answer: A: UV diffraction 
Explanation: Ninhydrin test and diazo reactions can identify individual amino acid, e.g. diazo reaction is given by histidine or tyrosine. So, an intact peptide bond is not necessary for this reaction, as they can be positive with an individual amino acid.
UV diffraction is used to identify higher order structure (secondary, tertiary, quaternary). Thus, non-covalent, as well as covalent (peptide) bonds should be intact.