Practice Questions

TLS Online TPP Program

#Question id: 3820

Meselson and Stahlʹs experiments involved growing E. coli on a medium containing 15N (heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only 14N. DNA samples were obtained for analysis after one, two and three rounds of replication (generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the 14N medium?

#Unit 3. Fundamental Processes

One with DNA containing both 15N and 14N.
Two, one with DNA containing only 15N and one with DNA containing only 14N.
Two, one with DNA containing both 15N and 14N and one with DNA containing only 14N.
Three, one with DNA containing only 15N, one with DNA containing both 15N and 14N and one with DNA containing only 14N.