Experiments have been used in the past to demonstrate that DNA is the transforming principle. Bacteriologists initially suspected that the transforming principle was a type of protein until they discovered that alcohol could be used to precipitate it, that proteases and lipases could not destroy it, and that it was rich in nucleic acids and had a molecular weight (National Human Genome Research Institute, 2018).
How 32P and 35S can be used to demonstrate that the transforming principle is DNA
An example of illustration for proving that the transforming principle is DNA, rather than the protein, uses elemental isotopes – radioactive phosphorous (32P) and sulfur (35S) to culture viruses. One group of viruses (A) is cultured in 32P while the second (B) is cultured in 35S. 32P can be used to label the DNA part of a virus because phosphorous is present in DNA but not in amino acids while 35S can be used to label the protein part since Sulphur is present in protein but not in DNA. Hence, the viruses in group A end up having radioactive DNA but not radioactive proteins whereas viruses in group B end up with radioactive protein but not DNA.
When the two groups of viruses are introduced to bacteria, the bacteria that get infected with viruses in group A become radioactive while those infected by viruses in group B do not show any radioactivity (Hershey & Chase, 1952). This confirms that viruses with radioactive DNA transfer their genes to the bacteria while viruses with radioactive protein do not transfer the protein material. This ultimately proves that the DNA is the transforming principle.
How the cell utilizes DNA during the process of transcription and translation
Transcription and translation are the mechanisms through which cells utilize genetic codes. During transcription, the cell decodes information that is encoded in the DNA to an RNA molecule in the nucleus (Pierce, 2013). Both DNA and RNA are made up nucleotide base chains that have slightly varying properties. The messenger RNA (mRNA) is the one that carries the information for making a specific protein and carries a message from the DNA from the nucleus to the cytoplasm (Pierce, 2013; Science Explained, 2018). The second part of the process, referred as translation, involves the utilization of the genetic message to form a protein (Pierce, 2013). It occurs when mRNA arrives at the ribosome and interacts with the transfer RNA (tRNA), which proceeds by reading the sequence of the message in the mRNA. Each sequence is called a codon and contains three bases which are normally codes for a particular amino acid. Amino acids are then assembled by to form a protein.
Figure 1: Illustration
In the above illustration, the mRNA reads the message coded in the DNA and transports it to the ribosome where it binds with tRNA to form amino acids. The first codon in the given sequence is GCA and would stand for amino acid alanine while the second base GGU would form Glycine. The cell continues with the translation process until the ribosome encounters a “stop” codon, which is essentially composed of a sequence of three bases that do not stand for a particular amino acid.
References
Hershey, A. D., & Chase, M. (1952). Independent functions of viral protein and nucleic acid in growth of bacteriophage. The Journal of general physiology, 36(1), 39-56.
National Human Genome Research Institute (NHGRI). (2018). Online Education Kit: 1944: DNA is. [online] Available at: https://www.genome.gov/25520250/online-education-kit-1944-dna-is-transforming-principle/ [Accessed 5 Jul. 2018].
Pierce, B. A. (2013). Genetics essentials: Concepts and connections. WH Freeman.Science Explained. (2018). From DNA to RNA to protein, how does it work?. [online] Available at: https://science-explained.com/theory/dna-rna-and-protein/ [Accessed 5 Jul. 2018].
