14. Virion structure general composition and symmetry Flashcards
Are viruses alive
No. They are unable to carry out metabolic reactions outside a host cell
What are definition and properties of a virus
Viruses are filterable agents that are obligate intracellular parasites. They can’t make energy or proteins independently from a host cell.
They have a naked capsid or envelope morphology
Can viral genome be both RNA and DNA
No, only one or the other
Do virus components replicate by division
No
What are the consequences of viral properties
Aside for not being living things, they need to be infectious to endure in nature. They mist be able to use host cell to produce their components and they must encode any required processes not provided by the cell. Viral components must self-assemble
Where can viruses exist
Extracellularly or intracellularly
What happens to viruses when they are extracellular
They are inactive because they can’t reproduce outside a host cell
What happens to viruses when they are intracellular
They commandeer host cells and use them to synthesize viral components from which mature progeny viruses are assembled and eventually released
Who can viruses infect
-Eukaryotes( animals, plant, fungi)
-Bacteria and Archaea
-Other viruses( viriophages)
On what properties can we do virus classification
-Genome type
-Virion structure
-Replication strategy
What’s virus classification by genome type
-Type of nucleic acid(DNA or RNA)
-Double helix or single helix and polarity
-Unsegmented or segmented
-Linear or circular
–If the genome is diploid( retroviridae)
What’s virus classification by virion structure
-Capsid symmetry: icosahedral, helical, complex
-Number of capsomeres
-Presence or absence of envelope
What’s classification of viruses by replication strategy
It’s shown by Baltimore classification system where:
1. dsDNA->mRNA
2.ssDNA->dsDNA->mRNA
3.dsRNA->mRNA
4.(+)ssRNA->(-)ssRNA->mRNA
5.(-)ssRNA->mRNA
6.(+)ssRNA->DNA/RNA hybrid->dsDNA->mRNA
7.dsDNA->ssRNA->mRNA
In what taxa can viruses be divided in
-Orders(-virales)
-Families(-viridae)
-Subfamilies(-virinae)
-Genus(-virus)
-Species
-Strains
-Types
What characteristics do viruses of the same specie share
They infect same host or a tissue, cause the same pathology and have same genomic map
What about genotypes of viruses?
Genotypes posses nucleotide differences that do not result in antigenic differences
What about serotypes of viruses
Serotypes differ in the presence of specific epitopes- are neutralized by different antibodies
What are viral strains
Viral isolates that have been well defined; like laboratory strains
How is mature virus particle called
Virion; it’s infectious( able to infect a cell)
What do the simplest virions consist of
-nucleocapsid(composed of nucleic acid, either DNA or RNA)
-protein ccoat-capsin
What does capsid do
It surrounds viral nucleic acid, thereby protecting the genome and often aids in its transfer between host cells
How can viruses be classified based on the envelope
.Enveloped viruses-virions covered by a lipid membrane
-Nonenveloped or naked viruses- viruses lacking the lipid membrane
What’s missing from the viruses
Ribosomes( for protein synthesis ) and mechanism for generating ATP. Cytoplasm is absent, and there is not enough enzymes (if any at all) to sustain cellular processes
What is virion structure defined by
Capsid symmetry and presence or absence of envelope
