The Taxonomy Of Viruses Assignment Paper

The Taxonomy Of Viruses Assignment Paper

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Chapter 6 entails viruses and their classification. Despite viruses being different from other forms of living things, they can be classified into various groups. The international committee on taxonomy of viruses provided a list of nine orders and 134 families of viruses in the year 2017. Table 6.6 is an illustration of the examples of the nine orders that were presented. From the table, a clear note of consideration is on the naming. The virus order name ends with ‘virales’, family name ends with ‘viridae’, and the genera name ends with ‘virus’ The Taxonomy Of Viruses Assignment Paper.

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Viruses are simply referred to as parasites that seize the control of genetic and synthetic functioning of the cell. Due to this reason, there are various modes of viral multiplication that also look at the effect of the virus to the host. The multiplication of viruses in animal host occurs in six different cycles. The first cycle is the Adsorption and the host range. This begins with the invasion of a virus to a susceptible host cell where they attach to the receptor sites on the cell membrane. The glycoproteins are usually the receptors of the cell membrane as shown in figure 6.8. For instance, the HIV attaches to the CD4 protein of the white blood cells. The range of host that a virus can infect in a natural setting is usually limited. For instance, Hepatitis B virus only affects the liver cells of a human, where this limitation is known as host range. Cells lacking compatible virus receptors are resistant to adsorption and viral invasion. The second cycle is the penetration or uncoating of animal viruses. The mechanism of animal viruses penetrating into the host cell is either by the whole virus or its nucleic acid as illustrated in figure 6.9. When penetration occurs through endocytosis as shown in figure 6.9a, the cell engulfs the entire virus in a vacuole. When the envelop and capsid are dissolved by the enzyme, the virus is said to be uncoated where this process release a viral nucleic ac8id into the cytoplasm. Another way of entry is through direct fusion of the viral envelop with the host’s cell membrane (figure 6.9b)The Taxonomy Of Viruses Assignment Paper. In this form, there is direct merging of the cell membrane with the envelop thus releasing nucleocapsid into the interior. Uncoating immediately occurs afterwards.

Synthesis is the other cycle that occurs after uncoating. In this cycle the main actions are replication and protein production. The process begins with the viral nucleic acid taking control of the host’s synthetic and metabolic machinery. The outcome of this action will depend on whether the nucleic acid is a DNA or RNA. In the case of a DNA, with an exception of poxviruses, they enter into the nucleus of the cell, replicated and stored there. In the case of RNA with an exception of retroviruses, they are replicated and stored in the cytoplasm. Figure 6.10 shows an example of RNA process using a positive strand virus model such as rubella. Immediately upon entry, the viral nucleic acid begins synthesizing the building blocks for new viruses. The +ssRNA, which immediately serves as mRNA upon entry begins being translated into viral proteins for further replication to occur (figure 6.10a)The Taxonomy Of Viruses Assignment Paper. The host machinery the replicates the + strand to -ssRNA. It is the RNA that becomes the template for the creation of more +ssRNAs used as the new genomes of the new viruses. Some viruses are well equipped with the necessary enzymes for synthesis of viral components while others utilize those of the host. Some viral enzymes, spikes and capsid are synthesized on the ribosomes of the host using the host’s amino acids. Retroviruses turn their RNA genomes into DNA as noted in figure 6.10b. The DNA on the other hand follow the same steps as those of the RNA. However, the steps in the synthesis process are different. The process begins with division of the dsDNA as shown in figure 6.11a. DNA enters nucleus during the early states where several genes get transcribed into messenger RNA. The newly transcribed RNA moves into the cytoplasm for translation of viral proteins required to replicate viral DNA. The process occurs in the nucleus where the host’s polymerase is utilized in the process through some viruses such as herpes virus which have its own polymerase. Finally, the last cycle of virus replication is the assembly of animal viruses. It comes about when mature particles of viruses are constructed from the growing pool of parts towards the end of the cycle. In most cases, the capsid is laid down as an empty shell that serves as receptacle for the nucleic acid strand. As shown in figure 6.12, electron micrographs taken at this time show cells containing masses of viruses. The insertion of the viral spikes into the cell membrane of the host so that they can be picked as virus buds off with it envelop is the event leading to release of enveloped viruses. The Taxonomy Of Viruses Assignment Paper