Radioactivity in the Insoluble Radioactivity in the Soluble Strain Treatment Fraction (epm*) Fraction (cpm) Normal No UV <100 <40 Normal 357 UV-treated, incubated 2 hours at 37°C 940 Mutant No UV <100 <40 Mutant UV-treated, 890 <40 incubated 2 hours at 37°C Source: Adapted from R. P. Boyce and P. Howard-Flanders (1964), Release of ultraviolet light-induced thymine dimers from DNA in E. coli K-12. Proc Natl Acad Sci USA 51, 293–300. *The abbreviation cpm stands for "counts per minute," which is a measure of the number of radioactive emissions from the sample.
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.
Richard Boyce and Paul Howard-Flanders conducted an experiment
that provided biochemical evidence that thymine dimers are
removed from DNA by a DNA repair system. In their studies, bacterial
DNA was radiolabeled so the amount of radioactivity reflected
the amount of thymine dimers. The DNA was then
subjected to UV light, causing the formation of thymine dimers.
When radioactivity was found in the soluble fraction, thymine dimers
had been excised from the DNA by a DNA repair system.
But when the radioactivity was in the insoluble fraction, the thymine
dimers had been retained within the DNA. The following table
illustrates some of the experimental results involving a normal
strain of E. coli and a mutant strain that was very sensitive to killing
by UV light:
Explain the results found in this table. Why is the mutant strain
sensitive to UV light?
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