LABORATORY REVIEW
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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one high-density and one low-density band
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One intermediate-density band
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one high-density and one intermediate-density band
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one low-density and one intermediate-density band
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Detailed explanation-1: -The observation of one high density and low-density band is not seen since the experiment was conducted for two generations in the 14N medium. After two rounds of DNA replication, no high-density band formation is observed because the E. coli was moved to the 14N medium. Therefore, the given option is false.
Detailed explanation-2: -coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged.
Detailed explanation-3: -coli fully labelled with N15N15 is allowed to grow in N14N14 medium, then after fist genertion of replication one of the two strands would have N15 and the other strand would have N14. The two strands of DNA molecule of the first generation bacteria have different density and resemble parent DNA.
Detailed explanation-4: -Therefore, starting with 15N15N DNA in E. coli, after 60 minutes, the percentage of DNA with 15N15N, 15N14N and 14N14N will be 0%, 25% and 75% respectively.
Detailed explanation-5: -Ten E. coli cells with 15N-dsDNA are incubated in medium containing 14N nucleotide. After 60 minutes, 60 E. coli cells will have DNA totally free from 15N.