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Are Viruses Alive? Origin of the Viruses 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)

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Are Viruses Alive? Origin of the Viruses Coevolution --- viruses may have evolved along with cells

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  1. 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

  2. Viral Life Cycle: Injection Attachment Gene Expression Release Genome replication Assembly

  3. 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

  4. 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

  5. To Lysogenic Cycle

  6. 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

  7. HIV, a Retrovirus --- HIV has a particularly high mutation rate, as many as 1 million different viral genomes in each infected person

  8. 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

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