Sanger chain-termination DNA sequencing requires deoxyribonucleoside triphosphates for synthesis. Which of the following are needed as the standard dNTP substrates?

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:

• The method is “chain-termination”.
• Standard dNTPs drive processive synthesis; ddNTPs cause termination when incorporated.

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:

• dATP only, or subsets like dGTP and dCTP, or dTTP only: incomplete; synthesis across diverse templates would stall at missing bases.
• Only ddNTPs: would halt immediately; no readable ladders form.

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)