DNA (Deoxyribonucleic Acid)
Deoxyribonucleic acid, DNA, is the primary structure that carries the genetic material in cells of living organisms and some viruses. The DNA is made up of strands of nucleotides that are made up of nitrogenous bases, a phosphate compound and, a ribose sugar. The nucleotides form a ring or ladder that over lapses to form double helix strands of polynucleotides. DNA aggregates to form the chromosomes that are strictly found within the nucleus of the cell. Some DNA are found in the ribosomes outside the nucleus. In the DNA structure, the series of the bases is arranged, and the sequence in one strand of the DNA constitutes the genetic code (Griffiths, 2005).
A long chain of the bases that codes for specific information is referred to as a gene. The DNA strand is constituted of a series of genes. These genes determine the inherited characteristics that are phenotypically shown by an individual. The genes are the actual determinants of the various proteins that are to be synthesized by the body. The nitrogenous bases are classified into two groups: the purine that includes Adenine (A) and Guanine (G) and the pyrimidine comprising of Thiamine (T) and Cytosine (C). The bases are linked together by means of a hydrogen bond. The number of Thiamine is seen to equal the number of Cytosine while the amount of Adenine also equals the number of Guanine. During the linkage by the hydrogen bonds, Thymine will combine with Cytosine while Adenine combines with Guanine (Zheng et al., 2010). The pair of the bases that are linked are said to be complementary, and hydrogen bonds only link complementary, pairs of bases
RNA (Ribonucleic Acid)
The RNA (Ribonucleic acid) has almost the same composition as the DNA except that it is single-stranded and has a2`-hydroxyl in its structure. In its strand, the Thymine base is replaced with a Uracil base. The RNA is can form a three-dimensional structure that helps it to speed up the reactions in the body. RNA does not contain enough genetic materials as compared to the DNA. It does not catalyze reactions as effectively as the proteins. Three types of RNA exists. The types of RNA are ribosomal RNA (rRNA), transfer RNA (tRNA) and messenger RNA (mRNA) (Griffiths, 2005).
DNA Replication
The DNA is can replicate itself to form new strands that are exactly the same as the original. The replication adds more genetic material in the cells and is the basis of inheritance. The additional genetic material, due to replication, is carried to the offspring during the process of reproduction. Replication involves the unzipping of the double strand due to the action of enzyme helicase. Once the DNA stand is unzipped, enzyme DNA polymerase reads the templates from the original DNA and starts of the production of new nucleotides on the template strands. During the process of replication, some short fragments called Okazaki are formed. Enzyme Ligase binds together the fragments. Another enzyme called Nuclease, will remove the defective parts of the new nucleotide. When the process ends, two completely identical DNA strands will be formed (Lewin, 2000).
According to Malys and McCarthy (2010), it has been proved that genes codes for the specific amino acids to be synthesized. It, therefore, means that protein synthesis will take place from the information that is coded in the DNA. The processes involved takes place in a series. It starts with the transcription of the DNA into an mRNA that later translates into an amino acid sequence that eventually makes up a protein.
Transcription
Transcription involves the transcription factor proteins which binds the promoter towards the coding sequence. Then DNA-dependent RNA polymerase binds to the promoter; which is a complex molecule made up of a number of proteins (Zheng et al., 2010). The RNA polymerase then unwinds the DNA strands, reads it, and the production of the new RNA.
The enzyme RNA polymerase I transcribes rRNA, and enzyme RNA polymerase II transcribes hnRNA. This process, after some changes, forms mRNA that is used as a template for protein synthesis. Finally, RNA polymerase III transcribes tRNA. The mRNA is the exact RNA copy of the genes that will be involved synthesis of proteins. The rRNA is the RNA that moves into the ribosomes that is the site of protein synthesis. Transfer RNA (tRNA), transfers the correct amino acid to the ribosome during protein synthesis.
Translation
During the process of translation, generated mRNAs are placed into groups of three nucleotides called codons. The mRNA and tRNA migrates into the cytoplasm. The three code, AUG on the mRNA signals the interaction of the ribosome and the mRNA and with the anticodons UAC. The tRNA has a formyl-methionine attached to it. The formyl group is changed into an amide group which is the basic functional unit of an amino acid. Other codons will be translated in the same fashion that eventually develops along chain of peptides that are bonded together with peptide chains. When the stop signal is reached on the mRNA, the process stops, and the final amino acid is hydrolyzed back to its tRNA.
RNA Polymerase Inhibition effect in Deathcap Mushroom
The process of transcription produces RNA that will carry the coded genetic information out of the nucleus into the ribosomes in the cytoplasm. As stated earlier, the ribosome is the exact site for protein synthesis. A poison called alpha-amanitin, found in the death cap mushroom, Amanita phalloides, is very lethal on the RNA polymerase. This poison attacks RNA polymerase II and reduces its mobility and ability to bind to the DNA. It clogs the subunits of RNA polymerase together stopping the body from producing mRNA and hence translation and protein synthesis cannot take place. When this happens, there will be no new cells formed which severely affect the liver leading to death. (Dart, 2004).
Conclusion
It can be demonstrated that the DNA is a major component involved in the transfer of genetic information from the parents to the offspring. If the inhibitor substance, alpha-amanitin, is injected into the body, death will occur as it will inhibit the process of translation hence no new cells are formed. This concept has been used by scientist in their pursuit to replacing some defective characteristics in the human body. There are several gene project that tries to map all the genes present in the body for the correction of undesirable characteristics.
References
Dart, R. (2004). Mushrooms. In Medical Toxicology: Philadelphia, USA, Williams &Wilkins.
Griffiths, A. (2005). Introduction to Genetic Analysis (8th Ed.). W.H. Freeman and Company.
Lewin, B. (2000). Genes VII. New York: Oxford University Press.
Malys, N. & McCarthy, J. (2010). Translation initiation: variations in the mechanism can be anticipated. Cellular and Molecular Life Sciences 68 (6): 991–1003.
Zheng, W., Zhao, H., Mancera, E., Steinmetz, M. & Snyder, M. (2010). Genetic analysis of variation in transcription factor binding in yeast. Nature.
List of Diagrams.
Diagram 1: DNA Replication showing the Replication fork, helicase, Primase, etc.
Diagram 2: DNA Replication showing Okazaki fragments and DNA Ligase
Diagram 3: RNA Synthesis showing RNA polymerase, Template strand, etc.
Diagram 4: Protein Synthesis in the cytoplasm
