Lecture Objectives (Virology) After this lecture, students will be able to: 1. D
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Lecture Objectives (Virology) After this lecture, students will be able to: 1. Describe the components of a virus. 2. Describe how a viral envelope affects viral transmission and the cause of disease symptoms. 3. Explain the general steps of viral replication. 4. Distinguish between DNA and RNA viruses based on how they replicate 5. Describe some of the cellular changes induced by viral infection. 6. Differentiate between acute, persistent, chronic and latent viral infections. 7. List oncogenic viruses and the two main mechanisms of viral oncogenesisExplanation / Answer
1. The viral components include mainly consists of a viral genome which can be either DNA and RNA and a capsid which covers the viral genome.
2. The envelop of the viral contains glycoproteins. This glycoprotein is required for the identificaiton and binding to the receptor area in the host cell. Once bound to the host cell, the viral envelop get fused with the host cell membrane and viral genome get incorporated inside the host cell.
3. Viral replicaiton is consists of the following major steps:
i) attachment- in this step the viral get attached with the host cell with the help of glycoprotein present in the viral envelope. As this glycoprotein can identify and bind with specific receptor site on the host, the interaction of a partcular virus is specific for a defined host range.
ii)entry- In this step the viral genome get inserted into the host cell, while the viral envelope remain outside the host cell. In some instances, the virus get inserted with the viral envelope but inside the cell, the enevelope get destroyed and the viral genome get released.
iii) assaembly of viral genome and amplification- During this step, the viral genome replication process occurs. A DNA virus generally used host enzymes and proteins required for the replication and viral DNA get transcribed to mRNA and following translated to protein. Whereas, for RNA viruses, viral RNA get synthesized to genomic RNA and consequently to mRNA. In this situation host enzymes and proteins are used for the generation of viral capsids for assembly of the newly prepared viral genomes. Virus such as retrovirus used reverese transcriptase enzyme to convert viral RNA into viral DNA.
iv) release- in this stage the new virus particles or virions get released from the host cell. These new viruses further infect new host cell and the replicaiton proccess get continued.
4. DNA virus can be single stranded and double stranded DNA. DNA virus used DNA dependent DNA polymerase to replicate the new viral genome. For DNA viral replicaiton, the viral genome get inserted inside the nucleus of the host cell and uses host enzymes and peoteins required for DNA replication. Viral DNA get transcribed to mRNA and consequently to protein with the help of host cell machinery. Single strande RNA virus which is positive strand get directly translated to protein into cytoplasm. While negative strand RNA virus first get converted to positive sense RNA by RNA dependent RNA polymerase and then translated to protein. Double stranded RNA virus has different RNA molecules which are able to produce one or more than one protein. Retroviruses use reverese transcriptase enzyme to convert RNA and DNA and consequently the viral DNA get included into host genome and produce new virions.
5. When a virus attacked a host cell, the host cell shows structural changes which is known as Cytopathic cytopathogenic effect. As a result of the viral infection, the cell can either get lysed or lost the abiity to further reproduce. The structural effects includes round structure, get fused with other cells which are in adjacent areas and presence of inclusion bodies in cytoplasm or nucleus.
6. accute- in acute viral infeciton, the infection spreads rapidly, stays for a brief period and then get resoluted within few days.
persistent- In persistent infection, the symptoms associated with the viral infection stays for longer period of times. This takes place if the adavpative immune system get failed to inhibit the primary response.
Chronic- In some situaiton, the primary infection or the infection which are staying for longer periods get resolved, but stays in latent form inside the host body. This latent form may develop infection once again in a certain point of time.
latent- In latent virus infeciton, the virus remain in an latent or inactive stage for a longer periods of tie inside the host cell and do not proliferate. However, the viral genome remains in the host cell and in presence of some condiiton, the latent phase get changed to active stage and the viral genome being active starts to produce new viruses inside the host cell.
7. Some viruses are suspected to be associated with cancer or formaiton of cancer. These viruses are known as oncolytic virus suas as-Epstein-Barr virus, HPV or human papillomaviruses. The two mechanism of viral oncogenesis includes-i) insertion of viral oncogenes inside the host genome or ii) induction of proto oncogene or preexisting oncogenes inside the host cell.
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