How do we know what is genetic material?
DNA is a genetic material that carries hereditary information. The components of genetic material are the DNA and proteins located in the chromosome. The following evidence was done to know the genetic material that carried hereditary information. Experiments were done using viruses and bacteria.
Frederick Griffith performed the first experiment using two strains of bacterium single was pathogenic and the other was harmless. (Yakisan,2016). Are Griffith mixed heat-fixed a pathogenic stain with harmless living cell then he injected on the healthy mouse and the mouse died this means that some living cells become pathogenic. This phenomenon was known as transformation, this is the change of genotype and phenotype caused by the adaptation of foreign DNA.
The second test was performed by Oswald Avery and Collin Macleod to show that the transforming material was the DNA, it was illustrated further by Alfred Hershey when he used a virus known as the bacteriophage to show that the T2 is the genetic material of DNA. Related phage also T2 used their tails to attach to the host cell and inject their genetic material. The genetic material was transformed and the T2 and the phage reproduced. He determined that the injected DNA of the phage provided the hereditary material.
Another experiment was done by Erwin Chargaff showed that DNA was a genetic material that consists of nucleotides each containing a nitrogenous base, sugar, and a phosphate group. After the DNA was known to contain genetic material another experiment was done to show that it contained a hereditary by Maurice Wilkins and Rosalind Franklin using a technique called X-ray crystallography it showed that the DNA consists of two strands making a double helix which were antiparallel. The bases paired with each other adenine paired with thymine and guanine paired with cytosine. In 1953 Watson and Francis explained the key feature of DNA as the double-stranded helix, anti-parallel, the helix is right-handed and has uniform diameters.
What are four functions of genetic material and explain each step
1.Replication
DNA consist of two complementary strands and each acts as a template for synthesizing a daughter strand. During replication, the parent strands unwind then replicate to form a daughter strand. The semi-conservative model is when each double strand replicates and each daughter will have one old strand. Conservative and dispersive model each strand mixes the template and daughter strand.
Steps of replication.
- Replication starts at the origin of replication, enzyme helicase unwinds the DNA strand, enzyme primase attaches, and synthesizes RNA strand that acts as a primer about 5-10 nucleotides after replication. DNA polymerase1 removes RNA nucleotides and adds DNA nucleotides.
2.DNA polymerase catalyzes the elongation of the strand from 3 -5 direction by adding nucleotides synthesizing a leading strand. (Bleichert2017), To elongate lagging strand DNA polymerase works in the path of the replication fork and are synthesized from Okazaki fragment which is then joined by DNA ligase.
3.DNA polymerase proofread the new strand replacing any incorrect nucleotide, in case of any mismatch the DNA is repaired by repair enzymes
2.Gene Expression
This is where the DNA directs the formation of a protein. Two stages are involved in Transcription and translation
Transcription is synthesizing RNA using a DNA. It involves three steps
Initiation: DNA unwinds and RNA polymerase attaches at the promoter region initiated by transcription factors.
Elongation; RNA polymerase travels along the DNA strand adding nucleotides to the 3 ends of the growing RNA strand.
Termination: After the complete RNA has been transcribed. RNA polymerase stop transcription and mRNA is released for translation.
The translation is the formation of a protein from mRNA.It consists of two stages. (Kailasam,2020) The first stage is done by enzyme amino acyl-tRNA synthase that performs an accurate match among tRNA and amino acids. The second step is the correct match between tRNA anticodon and mRNA codon
Translation also involves three-stage
Initiation: this step brings mRNA, tRNA with first amino acid, and two ribosomal subunits. (Smith,2017) mRNA binds to the initiation site and small subunits move laterally the mRNA till it meets a stop Codon.
Elongation; amino acids are added to the growing strand. each accumulation involves elongation factor and protein that occur in three phases Condon recognition, peptide bond formation, and translocation.
Termination; it happens at the stop codon mRNA reaches the A place of the ribosome. This location receives a protein called release factor that leads to the addition of water instead of amino acid. This hydrolysis causes ribosomal subunits and other components to dissociate leaving the protein. The protein then undergoes post-translational modification.
- genetic material also stores hereditary information that is passed on to the offspring.
Reference
Bleichert, F., Botchan, M. R., & Berger, J. M. (2017). Mechanisms for initiating cellular DNA replication. Science, 355(6327), eaah6317.
Kailasam, S., Singh, S., Liu, M. J., Lin, C. C., & Yeh, K. C. (2020). A Hema class glutamine‐methyltransferase is involved in the termination of translation and essential for iron homeostasis in Arabidopsis. New Phytologist.
Smith, A. (2017). Lyapunov Stability Analysis of Initiation Process in DNA (Deoxyribonucleic Acid) Translation Using Petri Net. Applied Mathematical Sciences, 11(64), 3153-3162.
Yakisan, M. (2016). Are the Genetic Materials of Gametes and Somatic Cells Different? The Conceptions of Pre-Service Teachers. International Journal of Environmental and Science Education, 11(4), 409-420.