Viruses & Prions

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In this section, we'll be talking about "acellular life", although some might argue that these things aren't really alive. Perhaps this is a case where there is no black-and-white alive-vs-dead, but rather a gradation where some things might reasonably be considered more alive than others. (The caveat to this would be, then, how do you measure this? And if you can't, then is it a meaningful scientific distinction?)

What is a virus?

Phage lysing E.coli
E. coli lysing because of infect by bacteriophage T4 : R.Bijlenga via SciencePhotoLibrary

Viruses are DNAs or RNAs, usually encapsulated in protein &/or membrane, that infect a cellular host & use the host ribosomes & cellular machinery for replication. Viruses infecting all 3 Domains (Bacteria, Archaea & Eukarya) are common.

We'll be focusing on the evolutionary problem of viruses, in other words, where did they come from, in the lecture on viruses. For more information on the different kinds of viruses, viral structure & replication, host recognition, etc, etc, take Dr. Petty's Virology course!

What is a prion?

A prion is a conformation of a normal central nervous system protein. This alternative conformation is "self-replicating", in the sense that it catalyses the transformation of this protein in the normal conformation into the prion conformation. This cascade of conformation change in the protein can be transferred to other individuals by eating CNS tissue of affected animals. Accumulation of this protein in the prion conformation causes pathology in the animal - transmissible spongiform encepalophathies.

Mad cow
Mad cow : Calder Chism (Calderchism.com)

That is, this is what a prion is if you buy the Prion theory. This is the question we'll address, in the Discussion session on Prions.