Transcript Coevolution --- viruses may have evolved along with cells

Are Viruses Alive?
Origin of the Viruses
Coevolution --- viruses may have evolved along with cells
Retrograde Evolution --- viruses may have come from more
complex parasitic life forms through loss of “unneeded”
genes (Mimiviruses)
Escaped Genes --- viruses may have originated from genes
that were part of an organism’s genome but became
associated with an autonomous replicating element
(plasmid or transposon).
Viral Diseases:
--- can’t be treated with antibiotics
--- most dangerous human viral infections are new to humans
Viral Life Cycle:
Injection
Attachment
Gene Expression
Release
Genome replication
Assembly
Virial Quantitation
Agglutination, many animal viruses can cause the aggregation
and precipitation of red blood cells
Infectious Units, look for the effects of the virus on host cells
--- mix dilutions of the virus with cells (animal, plant
or bacterial), plate, and look for infected cells
--- with bacteriophages the infections usually result in cell
lysis and are visible as clearing zones on a
confluent plate (Plaque Forming Units, PFU)
--- many eukaryotic viruses don’t cause cell lysis and
infection can be harder to determine
Viral Genomes & Replication
--- compared to other replicating forms most viruses have
very small genomes (25 – 250 Kbp)
--- viral genomes are often characterized as sense (+, or coding)
and nonsense (-, or noncoding) when single stranded
--- most viral genomes make use of overlapping reading frames
to get more use out of their small genomes
To Lysogenic
Cycle
In its integrated form
the virus is replicated
along with the cell’s
own DNA.
--- the only way to “kill”
an integrated virus is to
kill the host cell
HIV, a Retrovirus
--- HIV has a particularly
high mutation rate, as
many as 1 million
different viral genomes
in each infected person
Even Simpler than Viruses
Viroids: plant pathogens composed of short, naked (no coat)
ssRNA’s
Prions: misfolded proteins that can catalyze the misfolding
of other protiens (recruitment)
--- cause diseases that look like viral infections