Section 3: Genetics, Cellular and Molecular Biology
CRISPR-Cas9 gene editing
Subtopic: Fundamentals of CRISPR-Cas9 gene editing
Question Statement:
Which one of the following is the basic principle of Sanger's DNA sequencing
method?
Options:
(A) Chain termination by incorporation of dideoxynucleotides
(B) Chain elongation by incorporation of dideoxynucleotides
(C) Release of inorganic pyrophosphate
(D) Chain cleavage by modification of dideoxynucleotides
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.23)**
**1. Governing Concept**:
- **Topic**: Recombinant DNA Technology & DNA Sequencing
- Sanger sequencing (dideoxy chain termination method) relies on DNA polymerase incorporating 2',3'-dideoxynucleoside triphosphates (ddNTPs). Because ddNTPs lack the 3'-OH group necessary for phosphodiester bond formation with the incoming nucleotide, their incorporation causes immediate **chain termination**.
**2. Option Analysis**:
- **Option (A) [Chain termination by incorporation of dideoxynucleotides] is CORRECT**: Fundamental operating principle of the Sanger enzymatic sequencing method.
- **Option (B) [Chain elongation by incorporation of dideoxynucleotides] is INCORRECT**: Dideoxynucleotides completely halt elongation rather than permitting it.
- **Option (C) [Release of inorganic pyrophosphate] is INCORRECT**: Principle underlying Pyrosequencing, not Sanger sequencing.
- **Option (D) [Chain cleavage by modification of dideoxynucleotides] is INCORRECT**: Maxam-Gilbert sequencing uses chemical cleavage; Sanger does not cleave chains.
**3. Final Answer**:
- **Correct Choice**: **A**
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