When Meselson and Stahl grew Escherichia coli in 15N medium for many generations and then transferred the cells to 14N medium for one generation, they found that the bacterial DNA banded at a density intermediate between that of pure 15N DNA and pure 14N DNA following equilibrium density centrifugation. When they allowed the bacteria to replicate one additional time in 14N medium, they observed that half of the DNA remained at the intermediate density, while the other half banded at the density of pure 14N DNA. What would they have seen after an additional generation of growth in 14N medium? After two additional generations?
Bacterial Genomics
The study of the morphological, physiological, and evolutionary aspects of the bacterial genome is referred to as bacterial genomics. This subdisciplinary field aids in understanding how genes are assembled into genomes. Further, bacterial or microbial genomics has helped researchers in understanding the pathogenicity of bacteria and other microbes.
Transformation Experiment in Bacteria
In the discovery of genetic material, the experiment conducted by Frederick Griffith on Streptococcus pneumonia proved to be a stepping stone.
Plasmids and Vectors
The DNA molecule that exists in a circular shape and is smaller in size which is capable of its replication is called Plasmids. In other words, it is called extra-chromosomal plasmid DNA. Vectors are the molecule which is capable of carrying genetic material which can be transferred into another cell and further carry out replication and expression. Plasmids can act as vectors.
1) When Meselson and Stahl grew Escherichia coli in 15N medium for many generations and then
transferred the cells to 14N medium for one generation, they found that the bacterial DNA banded at
a density intermediate between that of pure 15N DNA and pure 14N DNA following equilibrium density
centrifugation. When they allowed the bacteria to replicate one additional time in 14N medium, they
observed that half of the DNA remained at the intermediate density, while the other half banded at
the density of pure 14N DNA. What would they have seen after an additional generation of growth in
14N medium? After two additional generations?
2) Draw a diagram of replication that is occurring at the end of a double-stranded linear chromosome.
Show the leading and lagging strands with their primers (indicate the 5′ and 3′ ends of the strands).
What difficulty is encountered in producing copies of both DNA strands at the end of a chromosome?
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