Restriction endonucleases are bacterial enzymes that cleave duplex (double-stranded) DNA at specific nucleotide sequences. The mode of replication of the animal virus SV40 has been investigated by using restriction endonucleases that cleave SV40 DNA into a number of unique segments. Like most viruses, SV40 DNA is circular. The map positions of the 11 fragments produced by a pair of restriction endonucleases are shown on the next page. Immediately following a 5 or 10 minute pulse of radioactively labeled thymidine, labeled SV40 molecules that have completed replication during the pulse are isolated. These newly replicated DNA molecules are digested by the restriction endonucleases and the resulting fragments are analyzed for the relative amounts of pulse label they contain. The results are in the table below. Assume that at the time the label was added there was a random population of replicating SV40 DNA molecules in all possible stages of synthesis. From the information given below, decide whether SV40 replication is unidirectional or bidirectional, and assign the origin and terminus to specific restriction fragments. Relative amount of pulse label (corrected for fragment size and normalized to 1.0 for fragment A – meaning that the rest of the column’s numbers were divided by the numerical amount of pulse label fragment A contained) Fragment after 5 minutes after 10 minutes A 1.0 1.0 B 3.9 3.0 C 0.0 0.8 D 0.9 0.9 E 1.8 2.0 F 4.0 3.1 G 5.4 4.2 H 1.7 2.5 I 2.7 3.0 J 4.9 3.7 K 2.4 2.9
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.
Restriction endonucleases are bacterial enzymes that cleave duplex (double-stranded) DNA at specific
The map positions of the 11 fragments produced by a pair of restriction endonucleases are shown on the next page. Immediately following a 5 or 10 minute pulse of radioactively labeled thymidine, labeled SV40 molecules that have completed replication during the pulse are isolated. These newly replicated DNA molecules are digested by the restriction endonucleases and the resulting fragments are analyzed for the relative amounts of pulse label they contain. The results are in the table below. Assume that at the time the label was added there was a random population of replicating SV40 DNA molecules in all possible stages of synthesis.
From the information given below, decide whether SV40 replication is unidirectional or bidirectional, and assign the origin and terminus to specific restriction fragments.
Relative amount of pulse label (corrected for fragment size and normalized to 1.0 for fragment A – meaning that the rest of the column’s numbers were divided by the numerical amount of pulse label fragment A contained)
| Fragment | after 5 minutes | after 10 minutes |
| A | 1.0 | 1.0 |
| B | 3.9 | 3.0 |
| C | 0.0 | 0.8 |
| D | 0.9 | 0.9 |
| E | 1.8 | 2.0 |
| F | 4.0 | 3.1 |
| G | 5.4 | 4.2 |
| H | 1.7 | 2.5 |
| I | 2.7 | 3.0 |
| J | 4.9 | 3.7 |
| K | 2.4 | 2.9 |
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