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Terms in this set (35)
Compare and contrast bacteria and viruses
Viruses are smaller than bacteria
Obligate intracellular parasite
Genome is either DNA or RNA, but not both
No ATP generating mechanism.
Have a Capsid or a protein coat that encapsulates and protects its nucleic acid from the environment
How are viruses specific for their host cells?
There are specific host attachment sites and cellular factors that viruses are attracted to. This is known as the host range.
Protein coat that encapsulates the nucleic acid. Structure is ultimately determined by the nucleic acid and accounts for most of the mass of a virus, especially small ones. Composed of small protein subunits called capsomeres. Some viruses, the capsid is covered by an envelope which usually consists of a comnination of proteins, lipids, and carbohydrates.Â
Four Major characteristics:
-Type of nucleic acid found in the virion (RNA or DNA)
-symmetry and shape of the capsid
-presence or absence of an envelope
-size of the virus particle
Family name ends in...
Genus name ends in...
-share same genetic information and host (ecological niche)
-Common names are used and are not italicized or capped
-subspecies are designated by a number
Genetic Content - DNA viruses
almost all that infect animals are double stranded
Genetic Content RNA
almost all are single stranded
exception Reoviridae (double stranded)
Positive strand RNA (+RNA)
single stranded sense that can act directly as mRNA
Negative strand RNA (-RNA)
consists of single stranded antisense that must be transcribed to + before it can be used as mRNA
Single stranded RNA is copied by reverse transcriptase into a DNA genome within the host cell.
Small DNA Viruses
replicated by the host DNA polymerase -Papovaviridae
Large DNA viruses
have their own replication machinery
RNA and Retroviruses are...
small but need their own polymerase
How are animal viruses cultured?
Can only replicate in living things.
Animal Models for cultivation
laboratory animals: rabbits, mice, rats, hamsters
Embryonated chicken eggs for cultivation of viruses
provides a variety of different tissues which allow the growth of a wide variety of viruses.Â
Cell culture for cultivation of viruses
most widely used and most powerful hosts for cultivation and assay
Primary cell culture
culture of cells from original tissues that have been cultivated in vitro for the first time.
Can be established from whole animal embryo or selected tissues in adult, newborn, or embryos
Only able to grow for a few passages as diploid cells
Secondary Cell lines
cells that have picked up a mutation that allows them to be passaged for about 50 generations
Continuous cell culture
cells that are capable of growing for prolonged, perhaps indefinate lengths of time. (generally derived from malignant tissues)
Used to quantitate infectious virus particles
Cells are grown as a lawn
They are then infected with the virus
The liquid growth medium is replaced with a semi solid one so any virus particles cannot move far
Plaques is produced then virus particle infects a cell, replicates, and kills that cell
surrounding cells are infected with newly replicated viruses and they too are killed
This process repeats several times
What general techniques are used to identify viruses?
Virus Replication for DNA animal virus
Entry and uncoating
Attachment (DNA virus)
virion attaches to cell
Entry and Uncoating (DNA virus)
virion enters via receptor mediated endocytosis and DNA is uncoated capsid is digested by the cell in attempt to phagocytize or digest the contents of the vessicle (can also be released into the cytoplasm of the host cell)
Portion of DNA is transcribed and produces mRNA that encodes early viral proteins
Viral DNA is replicated and some viral proteins are made
capsid proteins are synthesized
virions mature by capsid proteins surround the nucleic acid
virions are released
Difference in Biosynthesis of RNA virus
Major difference is the different processes of mRNA formation among the different groups of RNA viruses
Can be cultured in vitro (in a plastic flask) if living cells are provided to them. The source of the living cells can be:
-cell culture (primary cell culture, cell lines)
-immortalized in vitro
the growth occurring before being transferred to another dish
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