According to scientists Hershey and Chase, DNA is the genetic material. In their experiments, p labelled DNA and s labelled DNA were allowed to infect bacteria. After infection, the cultures were blended to detach the viruses from the bacterial cell. The result was then centrifuged. The bottom was composed of bacterial pellets while the supernatant was consisting of viral particles (Campbell & Paradise, 2016). According to the scientists, bacteriophages composed of DNA and protein infected bacteria, their DNA enters the host's, but most of the protein fails to enter. The experiments proved that DNA and not protein carried the all the genetic instructions for infecting bacteria, therefore, proving that DNA is genetic. Hershey and Chase also tried to prove that DNA is the transforming principle (Prielhofer et al., 2015). The experiment settled a longstanding debate and was accepted as proof that DNA is the genetic material.
In their experiment, they demonstrated how 32P and 35s might be used to prove that the transforming principle is DNA. They inserted radioactive isotopes phosphorus-32 and sulphur-35 into different bacteriophages and allowed growth for four hours before bacteriophage introduction. When the bacteriophages infected the bacteria, the progeny had the radioactive isotopes contained in them. The procedure was performed once for each bacteriophage (Campbell & Paradise, 2016). They were allowed to infect unlabeled bacteria and the genetic material entered while coats of the bacteriophages remained outside the bacteria. Agitation and centrifugation were then done to allow for the separation of the coats from the bacteria. The bacteria were then lysed to release the bacterial phage progeny (Campbell & Paradise, 2016). The progeny labelled 32p remained labelled while the progeny tagged 35s were unlabeled. This confirmed that DNA, and not protein is the genetic material.
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Transcription is the process by which information in a DNA strand is copied into a new molecule of messenger RNA. Safe and stable stores of genetic material in the cell nuclei are found in DNA. Messenger RNA carries the same information as DNA, but unlike DNA, it is not used for long-term storage. It is not identical to DNA because its sequence is complementary to the DNA template even though it contains the same information. The transcription process is carried out by an enzyme called RNA polymerase and transcription factors. Transcription factors bind to specific DNA sequence to recruit RNA polymerase to the appropriate site of transcription. The transcription factors and RNA polymerase form a complex initiate, that is, the transcription initiation complex (Prielhofer et al., 2015). The complex initiates’ transcription that is; the RNA polymerase begins mRNA synthesis by matching complementary bases to the original DNA template strand. The new mRNA strand is elongated, and after a complete synthesis, the transcription process is terminated. The new mRNA copies are then used for protein synthesis in translation.
The translation process resides within the cell ribosome. Mature mRNA molecules from transcription leave the nucleus and travel to the cytoplasm where ribosomes reside. Ribosomes are composed of two units that are, the large 50s subunits and the small 30s subunits (Prielhofer et al., 2015). The two subunits existed separately but joined together on the mRNA molecule. They contain protein and specialized RNA molecules that is, ribosomal RNA and the transfer RNA. The translation begins with three initiation factor protein that binds to the 30s subunits of the ribosome (Prielhofer et al., 2015). The complex and transfer RNA bind to the mRNA forming the initiation complex. The next phase is the elongation phase where the ribosomes move along mRNA in the 5'- the to-3' direction which requires the translocation process in elongation of factor G. The final step in the translation process is the termination stage. Three termination codons are used at the end of the sequence in mRNA coding that is UAA, UAG and UGA. Transfer RNAs do not recognize these codons therefore in place of the transfer RNA; proteins called released factors bind facilitating the release of mRNA from the ribosome and a resulting dissociation of the ribosome.
References
Campbell, A. M., & Paradise, C. J. (2016). The Source of Genetic Information . Momentum Press.
Prielhofer, R., Cartwright, S. P., Graf, A. B., Valli, M., Bill, R. M., Mattanovich, D., & Gasser, B. (2015). Pichia pastoris regulates its gene-specific response to different carbon sources at the transcriptional, rather than the translational, level. BMC Genomics , 16(1), 167.
