Difficulty: Medium
Correct Answer: All of these (all four dNTPs are required)
Explanation:
Introduction / Context:
In Sanger sequencing, DNA polymerase extends a primer using normal deoxyribonucleotides (dNTPs) while occasional incorporation of a dideoxynucleotide (ddNTP) terminates extension. Understanding the role of both dNTPs and ddNTPs is essential.
Given Data / Assumptions:
Concept / Approach:
Polymerization requires the full set of dNTPs: dATP, dTTP, dGTP, and dCTP. ddNTPs are added at limiting ratios to terminate chains at specific bases. Without dNTPs, polymerase cannot extend, and sequencing would fail.
Step-by-Step Solution:
Verification / Alternative check:
Standard protocols specify a mixture of all four dNTPs plus small amounts of labeled or unlabeled ddNTPs.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing the role of ddNTPs (terminators) with dNTPs (building blocks); overlooking that balanced dNTP pools are critical for uniform read lengths.
Final Answer:
All of these (all four dNTPs are required)
Discussion & Comments