MICRO 5 Exam 3 Viral Replication
Describe how two distinct anti-viral medications work.
- Nucleoside analogs are competitive inhibitors of some enzyme that is responsible for genome replications. - Viral-Cell Fusion inhibitors bind to the viral surface proteins so it can't attach to the host cell. - Small interfering RNA forms base pairs with viral RNA and our cells see theta as foreign and destroy it.
What are the main structural components of all viruses? Describe these components. Describe the structure that is unique to enveloped viruses. What determines the host range of a virus?
- Structural components of all viruses: DNA or RNA and a protein coat. DNA or RNA are instructions for reproduction and transmission. The protein coat protects the virus's nucleic acid. - The structure unique to eneveloped viruses is the phospholipid bilayer. - Proteins on the surface of the virus and proteins on the surface of the host have to fit together like lock and key which is what determines the host range of a virus.
What is the basic scheme of the viral infection cycle? Describe each step.
1. Attachment: Virus attaches to host cell by viral proteins bringing to specific host cell receptors found on surface of the host cell. 2. Penetration: For non-enveloped viruses, it enters the host by endocytosis. For enveloped viruses, they enter by their envelopes fusing with the host's membrane. 3. Uncoating: The capsid is digested, releasing the nucleic acid into the cell's cytoplasm. 4. Biosynthesis: 2 phases: early is replication of genome, and late is production of the capsid. DNA and RNA viruses use different replication strategies. 5. Maturation & Release: New viral nucleic acid and capsid are assembled to form the complete nucleocapsid, and are then released into the extracellular space from the cell by cell lysis (non-enveloped) or by enveloped viruses budding out of the cell taking some host membrane with it. Process repeats.
Describe just the biosynthesis stage of infection by DNA viruses that infect animal cells.
Early transcription and translation make enzymes to replicate the viral DNA which takes place in the nucleus. Viral DNA replication in the nucleus occurs and once that's far enough along, late transcription and translation happens and capsids are produced in the cytoplasm. Capsids will then go into the nucleus.
Compare the strategies that Ebola and HIV take and relate that to their success in spreading through the human population.
Ebola: Infects only a few hundreds of people at a given time. Immediate viral replication and host cell death, then moves onto the next host. HIV: More successful at spreading through the human population, and has spread to millions of people throughout the world. Persistent viral infection where HIV hangs our in a host cell and viral DNA is integrated into host chromosome by recombination of the provirus. Can exist for many years without causing symptoms to host and can still spread from person to person.
What are the unique events during the biosynthesis stage of retroviruses? Describe these events and any enzymes that are involved.
Reverse transcription where it takes the viral RNA and produces double stranded DNA by reverse transcriptase. The new viral DNA is transported into the host cell's nucleus and integrated as a provirus by the enzyme integrase.
Describe just the biosynthesis stage of infection by a plus strand RNA virus that infects animal cells. Be sure to highlight the first step (as separate from other steps) of this biosynthesis.
The first step is making the enzyme for the plus strand RNA viruses, producing RNA-Dependent RNA Polymerase. This enzyme copies the plus strand that serves as the template for transcription then synthesizes a complementary minus strand required for replication.
Describe just the biosynthesis stage of infection by a minus strand RNA virus that infects animal cells. Be sure to highlight the first step (as separate from other steps) of this biosynthesis.
The first step is when the pre-made virus brings RNA-Dependent RNA Polymerase and the negative strand is now a template for making the positive strand. This enzyme reads the negative strand and transcribes it into a positive strand. Next step is where the intermediate (positive strand) is transcribed into negative strands; positive strands are also used for translation to make capsid proteins.
Why might some people not consider viruses to be living organisms? What would be a good description of what a virus is and what it does?
Viruses cannot reproduce without host enzymatic systems and cannot metabolize nutrients. A good description of what a virus is and what it does can be related to intracellular "pirates" that pirate the host's systems in order to reproduce, which contains genes either RNA or DNA inside a protein coat and the genes contain instructions for their reproduction and transmission.
