to prove that the DNA in the chromosomes replicate semiconservatively, the experiment was carried out using
Answers
Schematic representation of models of DNA replication.
1. Conservative. Replication produces one helix made entirely of old DNA and one helix made entirely of new DNA.
2. Semi-conservative. Replication produces two helices that contain one old and one new DNA strand.
3. Dispersive. Replication produces two helices in which the individual strands are patchworks of old and new DNA.
Schematic representation of models of DNA replication.
Conservative. Replication produces one helix made entirely of old DNA and one helix made entirely of new DNA.
Semi-conservative. Replication produces two helices that contain one old and one new DNA strand.
Dispersive. Replication produces two helices in which the individual strands are patchworks of old and new DNA.
_Image modified from "Basics of DNA replication: Figure 1," by OpenStax College, Biology (CC BY 3.0)._
Semi-conservative replication. In this model, the two strands of DNA unwind from each other, and each acts as a template for synthesis of a new, complementary strand. This results in two DNA molecules with one original strand and one new strand.
Conservative replication. In this model, DNA replication results in one molecule that consists of both original DNA strands (identical to the original DNA molecule) and another molecule that consists of two new strands (with exactly the same sequences as the original molecule).
Dispersive replication. In the dispersive model, DNA replication results in two DNA molecules that are mixtures, or “hybrids,” of parental and daughter DNA. In this model, each individual strand is a patchwork of original and new DNA.
Most biologists at the time would likely have put their money on the semi-conservative model. This model made a lot of sense given the structure of the DNA double helix, in which the two DNA strands are perfectly, predictably complementary to one another (where one has a T, the other has an A; where one has a G, the other has a C; and so forth)^{2,4}
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. This relationship made it easy to imagine each strand acting as a template for the synthesis of a new partner.
However, biology is also full of examples in which the “obvious” solution turns out not to be the correct one. (Protein as the genetic material, anyone?). So, it was key to experimentally determine which model was actually used by cells when they replicated their DNA