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ID 16469

Problem 20: A half DNA ladder is a template for copying the whole.

Description:
Explore other theories on DNA replication.
Transcript:
HI! Meselson and Stahl showed that DNA replication is semi-conservative. In addition to the semi-conservative theory of DNA replication, two additional models were originally proposed: conservative and dispersive. In the conservative replication model, the parental DNA molecule is preserved, and the daughter DNA contains two newly synthesized strands. In the dispersive replication model, the strands of the daughter DNA molecule contain pieces of parental and newly synthesized DNA. If DNA is made conservatively, and you performed the Meselson-Stahl 15 N / 14 N bacterial growth experiment, what type of DNA banding pattern would you see after the density gradient spin? Mouse over each choice. same banding pattern as Meselson and Stahl. (No, this is the DNA banding pattern of semi-conservative replication.) same as Meselson and Stahl, but the 14 N and 15 N bands have switched places. (No, the 14 N band is not lower than the 15 N band.) The first generation tube will have 14 N and 15 N bands; the second generation will also have both bands but the 14 N band is darker. (That is correct) In both the first generation and second generation tubes there is one intermediate band. (No, there should be 14 N and 15 N bands in the 1st and 2nd generations.) If DNA is replicated conservatively, then in the first generation of a 15 N / 14 N bacterial growth experiment, the parental DNA would contain only 15 N, and the daughter DNA molecule would contain only 14 N. No intermediate band would result. same banding pattern as Meselson and Stahl. (No, this is the DNA banding pattern of semi-conservative replication.) The first generation tube will have 14 N and 15 N bands; the second generation will also have both bands but the 14 N band is darker. (No, this is the DNA banding pattern of conservative replication.) The 1st generation tube will have 1 intermediate band; the 2nd generation tube will have 1 intermediate band and another slightly higher. (That is correct) Instead of bands, the first generation and second generation tubes will have a smear between 14 N and 15 N positions. (No, there should be unique DNA bands instead of a smear.) In the dispersive model of DNA replication, each strand of the daughter DNA molecule is a mixture of old and newly synthesized DNA pieces. If the pieces were all the same size, then a single intermediate band would be present in the first generation. After another round of replication, more 14 N would have been incorporated, giving rise to a single "lighter" band in that tube. Now, what if in the dispersive model of DNA replication, the pieces of old and newly synthesized DNA were not always the same sizes? Mouse over each choice. same banding pattern as Meselson and Stahl. (No, this is the DNA banding pattern of semi-conservative replication.) The 1st generation tube will have 1 intermediate band; the 2nd generation tube will have 1 intermediate band and another slightly higher. (No, this is the DNA banding pattern of conservative replication.) The first generation tube will have one intermediate band; the second generation tube will have one intermediate band and another one slightly higher. (No, this is the DNA banding pattern of dispersive replication if all the segments were of equal size.) Instead of bands, the first generation and second generation tubes will have a smear between 14 N and 15 N positions. (That is correct.) If DNA was made in pieces as predicted by the dispersive model, and the lengths of these pieces were not equal, then DNA molecules with different amounts of 14 N and 15 N could be made. Each would have a different density, therefore giving rise to a "smear" between the 14 N and 15 N in the first and second generations. CONGRATULATIONS!!! YOU'RE SO SMART! Click here to try the problem again.
Keywords:
meselson and stahl, dna replication, density gradient, dispersive replication, semi-conservative
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