Below you have the sequence of both strands of a particular DNA segment. 5\'TTCA

Question

Below you have the sequence of both strands of a particular DNA segment. 5'TTCATAAAACCTA3' 3'AAGTATTTTGGAT5' So, let's say that you decided to artificially replicate this particular segment in the lab (this is totally a thing that scientists do; more on that in the next unit) in a solution containing radioactively labeled guanine nucleotides. Will both daughter strands be radioactive? Explain your choice. What if you replicated this segment in a solution containing radioactively labeled adenine nucleotides? Would both daughter strands be radioactive? Explain.

Explanation / Answer

Ans. Given, guanine nucleotide present in the PCR mix (reaction mixture) radioactive.

DNA replication follows semiconservative mode in PCR, too. The two new daughter DNA copies produced through semiconservative mode consist of one parental strand and one newly synthesized. Since the newly synthesized strands. Therefore, the guanine residues, if any, in these daughter strands will be radioactive.

5’- T T C A T A A A A C C A T -3’         -parent strand 1

3’-A A G T A T T T T G G T A -5’         - parent strand 2

After replication, we get,

5’- T T C A T A A A A C C A T -3’         -Daughter strand 1 (complementary to parent strand 2 )

3’-A A G T A T T T T G G T A -5’         - Daughter strand 2 (complementary to parent strand 1)

Note that only one daughter strand will be radiolabeled (bold, underlined) because it only consists of guanine nucleotides.

The other daughter strand does not have guanine, so it will not be radiolabeled.

Part 2: Yes.

If the reaction mixture has radiolabeled adenine nucleotides, both the daughter strands will be radiolabeled because both strands contain adenine (bold, underlined).

5’- T T C A T A A A A C C A T -3’        -Daughter strand 1 (complementary to parent strand 2 )

3’-A A G T A T T T T G G T A -5’        - Daughter strand 2 (complementary to parent strand 1)

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