Answer the following in sentences . ( In Microbiology terms) 1. How does a virus
ID: 176054 • Letter: A
Question
Answer the following in sentences . ( In Microbiology terms)
1. How does a virus differ from a cell?
2. Discuss why viruses are considered infectious "particles" on the borderline between living and non-living. Describe what advantage they get from living inside a host.
3. What is the chemical composition of a capsid and envelop?
4. What kind of enzymes can be found inside a virion? Why are they there?
5. Define viral species. Discuss the taxonomy of viruses: classification and naming of viruses
Explanation / Answer
1.
Cells contain everything required for life. They eat, rest, reproduce, and respond to external stimulus. They have various organelle and macromolecules that enable them perform their activities. Membranes of cells maintain potential across the membrane the activity of which is responsible for most of the life activities. Cell contain DNA, RNA, Enzymes, organelle like ribosomes, mitochondria, nucleus, all of which perform definite functions. The cytoplasm of a cell hosts various macromolecules which perform various functions. Cells can divide by themselves and have all the machinery to serve the purpose.
Viruses are obligate intra-cellular parasites. They are just chemical particles outside a living host. They lack an active membrane and organelle. Only inside a living host, they replicate and form their progeny. They lack their own metabolic machinery. They contain only few biomolecules.
2.
Virus are termed infectious particles since outside a live host, they behave like chemical particles only. They cannot perform any activity outside a living host. They are active only inside the host cell.
3.
Capsid is composed of proteins. The protein monomers that make up the capsid are called capsomeres. Each capsomere may be composed of a single polypeptide or multiple subunits of polypeptides.
The composition of envelop varies with the type of host a virus infects. The envelope of a virus is derived from its host during release of the progeny virions. While the lipid bilayer remains as such, virus may remove some of the proteins of the host or they may add their own proteins/glycoproteins to the membrane. Thus, virus modifies the membranes before they bud out from the host cell.
4.
Most of the virus contain enzymes that are required for their replication inside the host cell. Virus which have unusual genetic material (RNA viruses) carry their own enzymes required for replication. The most common enzymes carried by virus inside a virion are RNA- dependent RNA polymerases, RNA dependent DNA polymerases, integrase, etc(enzymes like neuraminidase and hyaluronidase are present on the virus surface but not inside a virion).
5.
Since virus are not classified as true living beings, their classification is still a subject of debate. According to the International Committee on Taxonomy of viruses, a species of virus is defined based on their genetic properties. Accordingly, virus species is defined as a polythetic class of virus that constitute a replicating lineage and occupies particular ecological niche.
The most common and widely accepted classification of virus is the Baltimore scheme of classification. According to it, the following are the virus categories:
Group I – double stranded DNA virus
Group II – single-stranded DNA virus
Group III – Double stranded RNA virus
Group IV & V– single stranded RNA virus
Group IV – Single stranded RNA virus with positive sense
Group V – single standed RNA virus with negative sense
Group VI – Positive sense SSRNA virus that replicate through DNA intermediate
Group VII – Double stranded DNA viruses that replicate through a single-stranded intermediate