Viruses Flashcards
what is a virus?
an infectious nucleic acid surrounded by protein
describe viruses? 5 things
they are acellular
they are smalled than bacteria
they are derived from cells of other organisms
they have DNA and RNA
they replicate, mutate and evolve independently.
what is viral phylogeny?
the analysis used for viral research
why is viral phylogeny difficult to resolve?
the viral genomes are tiny which restricts the analysis that can be done.
also there are no known viral fossils.
what is a virion?
a complete viral particle.
describe the structure of a virion:
consists of a nucleocapsid (which is composed of nucleic acid) and a protein coat called a capsid.
what does a capsid (protein coat) do?
the capsid surrounds the viral nucleic acid, protects the viral genome and helps in the transfer between host cells
where can viruses be found?
they can exit intracellularly or extracellularly.
extracellular - where the viruses are inactive
intracellular - viruses exit as a nucleic acid
viruses that affect bacteria are called?
bacteriophages (phages)
how can viruses be classified?
based on the capsid
what are the three types of capsid symmetry?
helical
icosahedral
complex
helical capsid:
shaped like a hollow tube with protein walls
e.g tobacco mosaic virus
infects a wide variety of plants, especially tobacco
icosahedral capsid:
a regular polyhedron with 20 equilateral triangular faces and 12 vertical.
e.g. chlorotic mottle virus
complex capsid:
a combination of helical and icosahedral shapes
what is poxvirus family?
the largest of animal viruses
give an example of binal symmetry
T2, T4 and T6 have a final symmetry because they have a head that resembles an icosahedral and a tail that is helical
what is a negative sense RNA virus?
they are a group of related viruses that have a negative sense, single-stranded genomes made of ribonucleic acid.
they use genome sense strands as the template for synthesis of all mRNAs.
what is a positive sense strand RNA virus?
single-stranded RNA virus
replication is not needed before protein translation can take place.
includes most of the viruses that cause crop diseases. they cause patches of dead cells that look like a mosaic.
what are retroviruses?
they are produced by reverse transcription.
it inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, changing the genome of that cell.
what are double-stranded RNA viruses?
viruses may have evolved repeatedly from single-stranded RNA ancestors.
What are double-stranded DNA viruses?
many common phages (bacteriophages) have double-stranded DNA viruses.
describe a viral infection.
most viruses have protein on their surface membrane that binds to receptors on the host cell.
the protein tricks the cell into taking the virus
once, inside the organism, and the viral genes are eventually expressed.
describe a viral infection.
most viruses have protein on their surface membrane that binds to receptors on the host cell.
the protein tricks the cell into taking the virus
once, inside the organism, and the viral genes are eventually expressed.
describe a viral infection.
most viruses have protein on their surface membrane that binds to receptors on the host cell.
the protein tricks the cell into taking the virus
once, inside the organism, and the viral genes are eventually expressed.
