Genetics and Evolution of Infectious Diseases Paper Example

Bacterial DNA replication

The typical eukaryotic DNA strand is linear, but the bacterial chromosome is circular with no free ends. The replication of bacterial chromosomes is illustrated by the bacteria Escherichia coli and Bacillus subtilis. Replication proceeds in three main stages, initiation, elongation and termination. These bacteria have a single replication origin, the oriC, which initiates the bidirectional replication of the chromosomes. The replication origin of E. coli bacterial contains DNA sequences recognized by the initiator DnaA protein. Upon binding to the origin, DnaA triggers other proteins and enzymes that will lead to the formation of two complete replisomes. The DnaA protein binds itself on the 9-mers, the DnaA box, on the origin chromosome. The initiator protein then attains the separation of the AT-rich 13-mer segments. DnaC delivers DnaB, a protein composed of six subunits that are identical, to the template. One hexamer DnaB protein clamps around every single DNA strand of the oriC and a pre-priming complex is formed. With DnaB being a helicase, the two molecules, in the opposite direction, the DNA strands away from the oriC. The strands are now ready for elongation and transformation.

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Trp operon

Tryptophan operon is a group of genes, transcribed together, responsible for the synthesis of the amino acid tryptophan. The trp operon consists of five structural genes; trp A, trp B, trp, C, trp D, and trp E. It also has repressive regulator gen, trp R, which contains a promoter for the binding of RNA polymerase and the synthesis of mRNA. The concentration of trp operon dictates its regulation. When the level of tryptophan is high in the growing bacterial medium, transcription for its biosynthesis is turned off, and when the concentration is low, biosynthesis is initiated once more. The on-off regulation system of trp operon is commenced by the trp aporepressor, a product of the trpR gene (Lehninger, Nelson,& Cox, 2008). This aporepressor cannot bind to the operator and therefore combines with the tryptophan molecule to form a repressor complex in high supply of tryptophan. In low amount, the operator gets exposed, and it initiates the synthesis of tryptophan. This amino acid is essential to the survival of bacteria as a majority of bacteria are parasitic. The gut bacteria, for instance, alter the bioavailability of tryptophan in the body by metabolizing it inadequate to the immune cells that fight against them.

Protein synthesis

Protein synthesis in bacteria takes place in two stages, transcription and translation. Transcription is the synthesis of mRNA utilizing the double-stranded DNA strand as the template. Transcription occurs in four major phases, template recognition, initiation, elongation, and termination. The RNA polymerase looks for the promoter, and once it finds it, the RNA binds itself to the 35 and 10 regions of the Sigma 70 promoter (Bohidar, 2015). The RNA polymerase then adds a ribonucleoside triphosphate. The termination of transcription in bacteria can either be rho-dependent or rho-independent. In the former, the rho factor binds the RNA region rich in cytosine and guanine and afterward binds the RNA downstream. When the rho comes in contact with the polymerase, the mRNA and the polymerase are terminated from the DNA template. In the rho-independent termination, the mRNA region rich of guanine and cytosine form a loop at the polymerase that is easy to melt. This causes transcription to stop and the mRNA and RNA polymerase released

Translation is the decoding and transfers of the mRNA sequencing information into the ordered amino acid arrangement to form a polypeptide. The initiation factors IF1, IF2, and IF3, are active during translation. IF3 brings the 30S subunits and the mRNA together, IF1 bind on the 30S A site blocking it, and the IF2 attached to the GTD will bring the initiator n-formyl methionyl- tRNA to commence the codon on the 30S subunit site P.

Bacterial conjugation

The formation of a bacteria with the human growth hormone begins when the hormone-releasing a pilus to the bacteria with an F plasmid. The relaxosome cuts the hGH at the origin of transfer. A portion of the relaxosome proteins are cut off by a relaxase, and one attaches to the t-DNA. A coupling factor recognizes the relaxase and connected to the pilus exporter which transports the t-DNA to the bacterial cell. Relaxase joins the two ends of the t-DNA to form a circular strand and this strand duplicates to form a double strand inside the bacteria. The strand from which the t-DNA was cut from also replicates to create a double strand. The bacteria end up having two DNAs, its DNA and the hGH DNA.

Mutation

Mutation can take place in a bacterial chromosome via nucleotide pair substitution including transversions and transitions or frameshift mutations through insertions or deletions. Mutations can be brought about by chemicals, radiations or even environmental changes. A mutated bacterial cell can be isolated from a cluster of other cells exposed to a mutagen via photoreactivation. Bacterial cells contain an enzyme photolyase which catalyzes the process of splitting pyrimidine dimers via the breaking of their covalent bonds.

Genetic crosses

When two hybrids are crossed, the ratio of the dominant or recessive genes depends on whether the cross was monohybrid or dihybrid. For the case of two monohybrid parent one tall, TT and one short, tt, the resultant generation will have four tall offspring who are carriers of the dwarfism gene. In a case of dihybrid crossing with both parents being tall but carriers, i.e., Tt, one kid will be tall, two will be carriers, and one will be a dwarf. The ratio of the recessive trait expressing itself will be 1:4.

Lytic and lysogenic cycle in bacteriophages

The lytic cycle is the process through which a viral phage enters a bacterial cell, reproduces and finally destroys that cell. The phage first interacts with the hosts bacterial surface receptors, followed by its entry into the cell(Tibayrenc,2017). This process is the follower by the biosynthesis of more phages, their maturation and the bursting and destruction of the host cell.

The lysogenic cycle is also similar to the lytic cycle. The phages penetrate the cell, undergo biosynthesis and maturation, but instead of killing the host like in the lytic cycle, the phage genome integrates into the bacteria and becomes part of it.

References

Lehninger, Albert L.; Nelson, David L. &Cox, Michael M. (2008). Principles of Biochemistry(5th ed.). New York, NY: W.H. Freeman and Company. p. 1128

Bohidar HB (January 2015). Fundamentals of Polymer Physics and Molecular Biophysics. Cambridge University Press.

Tibayrenc, Michel (2017-01-12). Genetics and Evolution of Infectious Diseases. Elsevier