Question

Which nucleotide lacks a \(3^{\prime}\)-OH group?

• A. ddTTP
• B. dATP
• C. dGTP
• D. dCTP

Hint:

\[ \boxed{ \begin{aligned} \text{dNTP} &\rightarrow \text{Has }3^{\prime}\text{-OH} \text{ddNTP} &\rightarrow \text{No }3^{\prime}\text{-OH} \rightarrow \text{Chain termination} \end{aligned} } \] ddNTPs are used in the Sanger DNA sequencing method.

Answer 1

The Correct Option is A

Step 1: Recall dNTPs and ddNTPs. Normal deoxynucleotides (dNTPs) possess a free \(3^{\prime}\)-OH group required for DNA chain elongation. Dideoxynucleotides (ddNTPs) lack this \(3^{\prime}\)-OH group.

Step 2: Identify the correct nucleotide. Since ddTTP lacks the \(3^{\prime}\)-OH group, DNA polymerase cannot extend the DNA chain after its incorporation. Thus, \[ \boxed{\text{ddTTP}} \] is the correct answer. Therefore, \[ \boxed{(A)} \] is the correct answer.