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Can someone please explain this to me in simpler terms? I don't understand the explanation....thanks.
"A cell is placed in a medium containing radioactively labeled thymidine. If the cell undergoes two rounds of replication while in this medium, the radioactivity will appear:
A . in both strands of all the DNA molecules.
B . in both strands of half the DNA molecules.
C . in one of the strands of every DNA molecule.
D . in both strands of half the DNA molecules; the other half of the DNA molecules will have one labeled strand.
The correct answer is choice D. DNA replication is semiconservative. This means that the parental strands of the double helix unwind and each then acts as a template for synthesis of a complementary strand. So, after the DNA has been replicated, two new daughter helices each consist of one parental strand base-paired to one newly synthesized strand. Now that we understand the way in which DNA replicates, lets get back to the question. If a cell is grown in a medium containing radioactively labeled thymidine--which is one of the nucleotides needed to synthesize DNA--after the first round of replication, all of the DNA molecules will have one labeled strand and one unlabeled strand. Why? Because the radioactively labeled thymidine will be incorporated into the newly synthesized strands. If the cell undergoes ANOTHER round of replication in the same medium, the same sequence of events will occur. The previously labeled parent strands, which are now the daughter strands, will base pair with free nucleotides, including more labeled thymidine, so these new daughter helices will have both of their strands labeled. The unlabeled original parent strands will base pair with the labeled thymidine, so these new daughter helices will have only one labeled strand. Hence, choice D is the correct answer; after the second round of replication, the label will appear in both strands of half the DNA molecules, and the other half will have only one labeled strand."
"A cell is placed in a medium containing radioactively labeled thymidine. If the cell undergoes two rounds of replication while in this medium, the radioactivity will appear:
A . in both strands of all the DNA molecules.
B . in both strands of half the DNA molecules.
C . in one of the strands of every DNA molecule.
D . in both strands of half the DNA molecules; the other half of the DNA molecules will have one labeled strand.
The correct answer is choice D. DNA replication is semiconservative. This means that the parental strands of the double helix unwind and each then acts as a template for synthesis of a complementary strand. So, after the DNA has been replicated, two new daughter helices each consist of one parental strand base-paired to one newly synthesized strand. Now that we understand the way in which DNA replicates, lets get back to the question. If a cell is grown in a medium containing radioactively labeled thymidine--which is one of the nucleotides needed to synthesize DNA--after the first round of replication, all of the DNA molecules will have one labeled strand and one unlabeled strand. Why? Because the radioactively labeled thymidine will be incorporated into the newly synthesized strands. If the cell undergoes ANOTHER round of replication in the same medium, the same sequence of events will occur. The previously labeled parent strands, which are now the daughter strands, will base pair with free nucleotides, including more labeled thymidine, so these new daughter helices will have both of their strands labeled. The unlabeled original parent strands will base pair with the labeled thymidine, so these new daughter helices will have only one labeled strand. Hence, choice D is the correct answer; after the second round of replication, the label will appear in both strands of half the DNA molecules, and the other half will have only one labeled strand."
