Question

Challenge Question If the two DNA molecules of the following composition were each replicated in a solution of adenine nucleotide triphosphate with all its phosphorus atoms in the form of the radioactive isotope 32 and the other three nucleotides are unlabeled, will both daughter molecules be radioactive? 5'-AAAAAAAAAAA-3' 3-TTTTTTTTTTTTT-5' 5'-ATATATATATATAT-3' 3 -TATATATATATATA-5' Yes for both molecules 1 and 2 No for molecule 1 and Yes for molecule 2 No for both molecules 1 and 2 Yes for molecule 1 and No for molecule 2 32P is not the correct isotope to label DNA

Answer 1

As you must know, DNA replication is a semi conservative method, in which one strand from duplex of daughter DNA is from parent.

So in case of the first DNA molecule, one strand is Adenine only, so naturally the opposite stand is of Thymine only.

So if two daughter DNA molecules are formed from it, one will have New Thymine strand while the other strand is New Adenine strand.

As the question stated, only Adenine is labeled.

So out of the two daughter DNA molecules, only one will be radioactively labeled.

While the Second DNA molecule, there's alternative Thymine and Adenine in both the strands. Thus if two daughter DNA molecules are formed both of them will have Radioactive labeled Adenine in it.

So we conclude that only One daughter DNA will be labeled from first molecule while in case of second molecule, both DNA daughter molecules will be labeled.

Thus the right option is 2.

No for molecule 1 and Yes for molecule 2.

Thank you