DNA segments Essay
The nascent mRNA strand generated from the process of transcription is usually subjected to a number of reactions that are altogether referred to as mRNA processing (Brown, 2002). These series of processes enables the mRNA strand to be ready for translation, which is technically known as the production of a protein product from an mRNA strand. One of the processes involved in mRNA processing is the capping of the 5’ end of the mRNA strand using a guanosine molecule. This capping thus produces a 7-methyl guanosine structure at the 5’ end of the mRNA strand.
In addition, the 3’ end of the immature mRNA strand is also attached to a polyA tail, which is technically a nucleic acid strand composed of repeating units of adenosine. The polyA tail protects the immature mRNA strand during transport from the nucleus, through the nuclear pore and out into the cytoplasm. Another step of mRNA processing is RNA splicing, which involves the removal of introns from the nascent mRNA strand (Campbell et al. , 2008). It should be understood that an immature mRNA strand is composed of coding and non-coding DNA segments.
The coding segments, also known as exons, comprise the actual gene that will be expressed during translation. On the other hand, the non-coding segments, or introns, are DNA segments that stabilize the entire mRNA structure, yet are required to be excised right before protein translation. RNA splicing thus removes all the introns in an mRNA strand, resulting in a mature mRNA transcript. Translation involves the attachment of the two subunits of a ribosome, namely the small and large subunits, allowing the reading of the nucleic acids at a pace of three nucelotides at a time.
Each set of three nucleotides is referred to as a codon, which in turn is translated into a specific amino acid by the transfer RNA (tRNA) molecule. The ribosome has two sites that directly interact with the mRNA strand, namely that A and the P site. The P site is involved with the reading of the codon by a tRNA molecule, of which the amino acid is then attached to the growing polypeptide chain that is held by another tRNA at the A site.
The first codon of every polypeptide chain is usually a methionine residue and this protects the polypeptide chain from disintegration and attack by enzymes within the cytoplasm. Once the tRNA reads any of the three stop codons, UAA, UAG and UGA, the tRNA detaches itself from the ribosome, thus resulting in the termination of the process of translation. Works cited Brown, TA. Genomes, 2nd ed. San Francisco, Wiley-Liss, 2002. Campbell, NA, Reece, JB, Taylor, MR, Simon, EJ and Dickey, JL. Biology: Concepts and Connections, 6th ed. New York: Benjamin Cummings, 2008.