Multiple choice

Four identical PCR reactions were carried out in tubes named I, II, III and IV. Besides the usual mix of dNTPs, each of the tubes respectively contained $\gamma$-32P dATP, $\beta$-32P dATP, $\alpha$-32P dATP and $\alpha$-32P rNTP. Which one of the tubes will have radiolabeled PCR product?

  1. Tube I

  2. Tube II

  3. Tube III

  4. Tube IV
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C Correct answer
Explanation

During PCR, DNA polymerase adds dNTPs to the growing strand by utilizing the alpha phosphate and releasing pyrophosphate from the incoming dNTP. Therefore, only alpha-32P dATP will be incorporated into the newly synthesized PCR product, whereas beta and gamma phosphates are cleaved off during the reaction.

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