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Description

The structure of Semiconservative Replication introduces new features of important biological importance. We have not forgotten that the particular pairings we proposed immediately suggested a possible mechanism for the replication of genetic material.

Watson and Crick (1953)

The most important aspect of the DNA structure Watson and Crick discovered was not that it gave scientists a three-dimensional model of the molecule. But that the structure seemed to reveal the mechanism by which DNA was copied.

As stated in their 1953 paper Semiconservative Replication, Watson and Crick strongly suspected the presence of certain base pairs. In the DNA double helix to provide a controlled system of DNA replication. However, years of follow-up research took place before the precise relationship between DNA structure. And replication could be understood, including a classic experiment by American geneticists Matthew Messelsen and Franklin Stahl in 1958.

Models for DNA Replication

Replication is the process of making copies of their DNA before cells divide. For example, in humans, each stem cell must copy a total of 6 billion base pairs of DNA before undergoing mitosis. The molecular details of DNA replication have been described elsewhere. And was not known until some time after Watson and Crick’s discovery. In fact, scientists are faced with more fundamental research questions before deciding on these details. Specifically, they wanted to know the exact nature of the DNA replication process.

Defining the Models

As mentioned above, Watson and Crick themselves had specific ideas about DNA replication based on the structure of the DNA molecule. In particular, the couple predicts that the reproduction will proceed in a “semi-conservative” fashion. According to the semi-conservative replication model. The two original DNA strands (ie, the two complementary components of the double helix) are split during replication; each strand acts as a template for a new strand of DNA, that is, each newly synthesized Double helix is a combination of an old (or original) and a new strand of DNA.

Create model-based predictions

When these three models were first proposed, scientists had some evidence of what happens at the molecular level during DNA replication. Fortunately, regardless of the underlying molecular mechanisms, these models provided different estimates of the distribution of old and new DNA in newly dividing cells. These estimates are as follows:

According to the semi-conservative model, after one round of replication, each new DNA becomes a double-stranded hybrid. Consisting of old DNA and a newly synthesized DNA strand. Then, during the second round of replication, the hybrids separate, and Semiconservative Replication each strand pairs with the newly synthesized strand. So only half of the new DNA double helix is ​​hybrid, and the other half is completely new. Each subsequent round of replication results in a new duplex that is less hybrid and more complete.

According to the traditional model, after one round of replication, half of the new DNA double helix consists entirely of old or original DNA, and the other half is entirely new. Then, during the second round of replication, each double helix is ​​completely replicated. Then, one-quarter of the double helix is ​​completely old and three-quarters brand new. Thus, each successive round of replication results in a greater proportion of completely new DNA duplexes. While the number of completely original DNA duplexes remains the same.

Depending on the scattering pattern, each round of replication produces hybrids or DNA double helices, which are fragments of both the original DNA and the new DNA Semiconservative Replication. Each subsequent round of replication produces a double helix containing large numbers of new DNA.

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