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Microbiology: mRNA synthesis and ssRNA viruses

1. Why is the synthesis of mRNA a central issue for all viruses?
2. Polio and HIV are both +ssRNA viruses that have very different strategies for replicating their genomes. After the viral genomes enter the cell (ie. post entry), describe the first step involved in replication of each genome. Your description can include a diagram and should cover 1) the name of the synthesis reaction that takes place, 2) any molecules that act on the viral genome 3) whether these molecules are viral or host in origin, 4) the product(s) of this first step, and 5) which cellular compartment step 1 takes place in.

3. (4pnts) What is cap stealing and why is it necessary for influenza replication?

4. A-C. (9pnts) Your roommate spends the night in the bathroom being rather ill. Motivated more by curiosity than common sense, you take a sample from the relevant location (you are very good friends with your roommate!) and make an extract. When this extract is applied to human cells in culture, you see the formation of plaques (indicating that the cells have died and lysed). You extract nucleic acid from the plaques and determine that it is 1 long continuous piece. When this is added to a mixture containing ribosomes and all the necessary components to synthesize proteins, you detect several proteins.

A. (3pnts). Of the classes of Viruses that we talked about, which kind of virus is this most likely to be. Provide reason(s) for your answer.

B. (3pnts). How can several proteins be made from the above nucleic acid (ie you only saw 1 long piece).

C. (3pnts). What does this imply about the activity of at least one of the proteins that are synthesized?

Solution Preview

1. Why is the synthesis of mRNA a central issue for all viruses?

The synthesis of mRNA is a central issue for all viruses because a virus is an entity that has only RNA or DNA as its main genome. Most viruses are have either DNA or RNA in its coat that codes for virus elements. Without the RNA, the virus is "metabolically inert"; that is, it is totally inactive. The virus that has no DNA or RNA usually contain only a protein coat or capsid. A virus depend on its genetic material DNA or RNA for metabolism. When a virus comes into contact with the host cell, it can insert its genetic material into its host and take over the host's functions. The virus can take over the host cell machinery and program the cells to produce the viral proteins instead of its own proteins.
Since no viral protein can be made until the viral mRNA is available in the viral genome, the nature of the type of RNA in the virion affect the strategy of the virus. (1) The virus life strategy depends on its type of RNA in the genome. There are plus-stranded RNA viruses where the viral RNA is in the same sense as mRNA and functions as mRNA because it can be translated to viral protein when infected into host cells. There are viruses that carry a negative-stranded RNA, which is in negative sense or complementary to mRNA. The negative-stranded RNA must be copied into plus-sense mRNA before translation of proteins can be done. (1) Other viruses have a double stranded genomic RNA and have different function than the mRNA. This viruses need to package their RNA polymerase to make their mRNA after infection. (1) Then, there are retroviruses that have a plus-sense virion RNA that does not function as mRNA upon infection. These RNA serve as template for reverse transcriptase to copied into DNA. Thus, synthesis of mRNA is a central issue for all viruses because single stranded RNA viruse are categorized into four classes based on the polarity of their RNA genomes. (2) The different polarity of the viral RNA genome will dictate the type of strategy for viral replication. (2)

2. Polio and HIV are both +ssRNA viruses have very different strategies for replicating their genomes. After the viral genomes enter the cell (ie. post entry), describe the first step involved in replication of each genome. Your description can include a diagram and should ...

Solution Summary

The synthesis of mRNA is a central issue for all viruses because a virus is an entity that has only RNA or DNA as its main genome. Most viruses are have either DNA or RNA in its coat that codes for virus elements. Without the RNA, the virus is "metabolically inert"; that is, it is totally inactive. The virus that has no DNA or RNA usually contain only a protein coat or capsid. A virus depend on its genetic material DNA or RNA for metabolism. When a virus comes into contact with the host cell, it can insert its genetic material into its host and take over the host's functions. The virus can take over the host cell machinery and program the cells to produce the viral proteins instead of its own proteins. Here, we will survey the characteristics and life cycle of virus and how they affect us.

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