Biology Sample Paper on Virology Med Term

Virology Med Term

Explain the Baltimore classification of viruses and the type of nucleic acid found in virions of each type.

Virus classification is the practice of placing viruses into groups based on their characteristics. Baltimore classification uses way of duplication, balance of the nucleic acid and the sense of the viruses in grouping them (Flint 2009). Grouping places the viruses in seven groups denoted with roman numbers, they are from i- vii. Group i viruses are always represented as ds DNA; they possess a double stranded DNA and include viruses like poxyviruses. Group ii viruses have solo stranded DNA and comprise of viruses such as parvoviruses. Group iii is another classification and they possess double stranded RNA genomes; reovirus is found here. Group iv have positive sense single-stranded RNA gnomes like the togavirus, they are commonly denoted as ssRNA (+). Group v has a negative sense single stranded RNA genome like the ones found in the rhabdovirus; commonly denoted as ssRNA (-). Group vi viruses possess a single stranded RNA that replicate through DNA intermediate, retoviruses are examples found in this group (Flint 2009). Group vii possess double-stranded DNA and use reverse transcriptase in replicating like witnessed in the hepadnaviruses (Flint 2009).

  • Compare and contrast the four types of nucleic acid polymerases and give an example of each

Archaearal RNA polymerase

The manufacture of RNA in the archaea is caused by a solitary type of RNAP. The archae RNAP is similar, physically and systematically to the bacterial RNAP and nuclear RNAP i-v (Flint 2009). An example in this category is the RNA polymerase ii (Flint 2009).

Viral RNA polymerase

RNA is created by the orthopoxviruses using RNAP that is systematically and anatomically related to eukaryotic and bacterial RNAP and is virally coded, creation of RNA in majority of the viruses use RNAP that does not relate to other RNAPs. Large quantities of the viruses use the same subunit DNA dependent RNAP. An example in this category is the poliovirus (Flint 2009).

RNA polymerase in bacteria

 mRNA creation is catalyzed in bacteria by one enzyme. RNAP is an enormous enzyme whose core has five subunits β’, β,ω, αI and αII. Sigma surges the specificity for promoters letting transcription instigation to correct sites while it diminishes the attraction of RNAP to non-specific DNA (Flint 2009). An example in this category is the E-box (Flint 2009).

RNA polymerase in eukaryotes

The numerous types of nuclear RNAP found in the eukaryotes is responsible for the manufacture of RNA (Flint 2009). They share many similarities among themselves and the bacterial RNAP. RNA polymerase has subunits that are denoted using roman numbers from i-v. They are liable for creation. Eukaryotic chloroplasts contain RNAP that has many similarities structurally and operationally to the bacterial RNAP. An example in this category is a poliprprotein (Flint 2009).

  • What is the molecular mechanism of RNA replication in poliovirus?

Poliovirus is a positive stranded RNA virus, so the genome bounded within the viral element can be used as a messenger RNA and instantly decoded by the host cell (Flint 2009). The virus causes virus-specific protein creation while barring the synthesis of cellular protein by hijacking the cells translation mechanism on its entry. Unlike the host cells RNA, the end of the poliovirus that is 5’ is highly designed and exceptionally long over 700 nucleotides (Flint 2009). Ribosome entry site is the viral area where conversion of the important RNA is done. Genetic mutation inhibits the viral protein formation in this section. The poliovirus mRNA is decoded as a solitary long polypeptide. The internal proteases auto-cleaves the peptide into about 10 explicit viral proteins. The process is assisted by the subsequent proteases (Flint 2009);

  • 3Dpol–   Its task is to duplicate and multiply the viral RNA genome and it is an RNA dependent polymerase
  • VPg- A small protein that is essential for synthesis of viral negative and positive strand RNA and it binds the viral RNA.
  • 2Apro and 3Cpro/3CDpro– These are in charge of cleaving the viral polypeptide.
  • 2BC, 2B, 2C, 3AB and 3B- These are proteins needed for virus replication using the protein complex got in them
  • Briefly discuss those ways in which mRNAs are processed in the nuclei of eukaryotic acid.

Capping, splicing and polyadenylation are the ways through which the mRNAs are processed in the eukaryotic acid


It is the process through which the introns are removed by changing the pre-mRNA. A protein complex known as spliceosme is the one in charge for splicing. In many instances, messages from the pre-mRNA are always spliced. Splicing in RNA molecules is catalyzed by themselves in some instances numerous diverse ways letting encoding of multiple proteins by a solitary gene (Flint 2009). After splicing has occurred, exons that can code proteins are left.


The medication of 5’ ends of the eukaryotic mRNA is known as capping. Capping takes place even before the eukaryotic is completed being manufactured by the RNA polymerase ii. The cap contains of a GTP that is methylated and attached to the rest of the mRNA (Flint 2009). Capped mRNAs are decoded to make proteins by the ribosomes very proficiently. Capping functions co- transcriptionally to transcription such that each is dependent on the other (Flint 2009).


The mRNAs have 3’ ends, which are accumulated with numerous hundreds of nucleotides through the process called polyadenylation. All eukaryotic mRNAs are meant to get a poly A tail that comprises the sequence AAUAAA about 11-30 nucleotides upstream to where the tail is added (Flint 2009). The messenger RNA is bound by some protein and a ploy a tail that prevent it from mortifying by exonucleases. The system of polyadenylation is vital in exportation of messenger RNA from nucleus and for transcription conclusion (Flint 2009). Once the RNA is transcripted from DNA, polyadenylation takes place. After this, the messenger RNA chain is cleaved through the action of endonucleases complex (Flint 2009). Cleaving of the primary RNA takes place at the poly-A addition site and at the 3’ end of the RNA 100-200 As are added. An unstable RNA is formed if this site is altered even slightly.

            Editing is another process although most of the times it is considered a minor process. It occurs when the messenger RNA alignment of nucleotide is altered creating an early stop codon that produces short protein (Flint 2009).


Flint, S. J., & American Society for Microbiology. (2009). Principles of virology: Vol. 2. Washington, DC: ASM Press.