Info

p= 1.B0

before transfer one cell to 14N generation after transfer to 14N

two generations after transfer to 14N

before transfer one cell to 14N generation after transfer to 14N

two generations after transfer to 14N

the location ol UNA molecules wittim the centriluge cell cen be determined by ultraviolet optics

DNA was thus shown to be a semiconservative process in which the single strands of the double helix remain intact (are conserved] during a replication process that distributes one parental strand into each of the two daughter molecules (thus, the "semi" in semi-conservative), These experiments ruled out two other models at the time: the conservative and the dispersive replication schemes (Figure 2-10). In the conservative model, both of the parental strands were proposed to remain together and the two new strands of DNA would form an entirely new DNA molecule. In this model, light DNA would be formed after one cell generation. In the dispersive model, wliich was favored by many at the time, the DNA strands were proposed to be broken as frequently as every ten base pairs and used to prime the synthesis of similarly short regions of DNA. These short DNA fragments would subsequently be joined to form complete DNA strands. This complex model would lead to DNA strands that would be composed of both old and new DNA (thus non-conservative) and would only approach fully light DNA after many generations of growlh.

Nucleic Acids Convey Genetic Information replicated; three are illustrated here. The experiments proposed by Mesebon and Stall I clearly distinguished itmcng these models, demonstrating that DNA was replicated serruconservativety.

FIGURE 2-10 Three possible mechanisms for DNA replication. When the structure of DNA was discovered, several models were proposed to explain how it was

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