Q.61 Given below are two statements :
Statement I : Sanger’s chain termination method is used for sequencing of a single stranded DNA by using
nucleotides and short DNA stretches.
Statement II : Sanger’s protein sequencing method uses 1-fluoro-2, 4-dinitrobenzene, dansyl chloride and
nucleosides for protein sequencing.
In the light of the above statements, choose the correct answer from the options given below :
1. Both Statement I and Statement II are true
2. Both Statement I and Statement II are false
3. Statement I is true but Statement II is false
4. Statement I is false but Statement II is true
Sanger’s chain termination method, commonly known as Sanger sequencing, is for DNA sequencing, while Sanger’s protein method uses specific chemical reagents—not nucleosides. The correct answer is option 3: Statement I is true but Statement II is false.
Statement I: True Explanation
Sanger’s chain termination method sequences single-stranded DNA using DNA polymerase, normal dNTPs (deoxynucleotides), and chain-terminating ddNTPs (dideoxynucleotides), plus a primer (short DNA oligonucleotide).
The ddNTPs randomly halt synthesis at each position, producing fragments separated by size on a gel or capillary electrophoresis to read the sequence.
This classic technique reads up to ~900 base pairs accurately, ideal for plasmids or PCR products.
Statement II: False Explanation
Sanger’s protein sequencing uses 1-fluoro-2,4-dinitrobenzene (DNFB or Sanger’s reagent) to label the N-terminal amino acid via nucleophilic substitution, forming a yellow DNP derivative identifiable post-hydrolysis.
Dansyl chloride later improved N-terminal detection with fluorescent derivatives, but neither method employs nucleosides (RNA/DNA building blocks).
Protein sequencing advanced to Edman degradation; nucleosides are irrelevant here.
All Options Evaluated
| Option | Description | Correct? | Reason |
|---|---|---|---|
| 1. Both true | Assumes both statements accurate | No | Statement II wrongly includes nucleosides |
| 2. Both false | Claims neither correct | No | Statement I correctly describes DNA method |
| 3. I true, II false | Matches facts | Yes | DNA uses nucleotides/short DNA; protein uses DNFB/dansyl chloride |
| 4. I false, II true | Reverses accuracy | No | DNA method is standard; no nucleosides in protein sequencing |
This distinction is key for exams in molecular biology or biotechnology, separating Sanger’s dual Nobel-winning contributions (DNA 1980, protein 1958).
