7 In terms of life cycle what are some unique problems faced

7.) In terms of life cycle, what are some unique problems faced by a (-) ssRNA virus? By a (+) ss RNA virus? Would a DNA virus have the same or similar problems to overcome? Why or why not? What strategies are employed by these different types of viruses to accomplish genome replication?

Solution

The enzyme viral polymerase is important for viral genome replication and trancription.

RNA is ribonucleic acid and RNA virus has the genetic material of RNA and this nucleic acid is single stranded RNA. RNA virus can be classified into two types based on sense or polarity, that is negative sense and positive sense virus. Viral RNA synthesis lacks proof reading.

Positive-sense RNA 5\' to 3\' can work as mRNA and directs the synthesis of protein that is transcription without the use of complementary RNA intermediate. Replication requires the enzyme RNA dependent RNA polymerase, capping enzyme, helicase, nucleoside triphosphatase and also the host cell protein. The replicase and the cis acting signal in the template regulates the relative levels of genomic RNA. As a result, RNA replication complex will be release from host membrane. The replication of RNA takes place in cytoplasm specifically in vesicle\'s membrane, mitochondrial membrane. The examples for positive sense viruses are picornaviruses, flaviviruses.The replication of positive sense RNA virus takes place in the surface of host cell membrane. The host ribosomes synthesis the proteins. The replication positive sense single strand RNA virus takes place in cytoplasm.

Negative-sense RNA 3\' to 5\' requires RNA dependent RNA polymerase has a sequence complementary to mRNA (ribonucleoprotein complex). For the synthesis of protein, this negative sense RNA should first be transcribed to positive sense RNA. The ribonucleoprotein complex act as template for replication, the newly synthesised viral RNA and complementary RNA will be packed as ribonucleoprotein complex The examples for negative-sense viruses are rabies viruses, mumps viruses, measles viruses.The replication of negative sense RNA virus uses protein-coated templates. There are two types in negative sense ssRNA viruses, they are the viruses with segmented genomes and the other one is viruses with nonsegmented genomes.

The replication of single stranded RNA virus is not as dependent on the cell cycle as that of DNA viruses.

References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908549/