Lec 16: Origins and Evolution of Viruses Flashcards
The origins and evolution of many cellular organisms can be inferred from….
But…
…fossils
…there is very little fossil record of viruses!
The discussion of the possible origins of viruses =
But…
highly speculative
…firm ground as sequencing of virus genomes enables the construction of phylogenetic trees and the monitoring of virus evolution as it occurs
All studies about viral origin is purely based on
sequence
Viruses are parasites of cells, so
there could be no viruses until cells had evolved.
which viruses came first, prokaryotic vs eukaryotic?
Prokaryotic viruses came first (before eukaryotic)
Where did viruses come from?
However, we speculate about…
Basically, we do not know!
…Possible ancestors of viruses
Possible ancestors of viruses:
- ) molecular precursors of cellular organisms
- ) Components of cells
- ) Intracellular micro-organisms
(Molecular precursors of cellular organisms)
Before cellular organisms had come into existence…
…RNA molecules evolved and developed enzyme activities (ribozymes) and the ability to replicate themselves
(Molecular precursors of cellular organisms)
Once cells had evolved perhaps some were…
…parasitized by some of these RNA molecules, which somehow acquired capsid protein genes —- possible 1st viruses = RNA viruses (not DNA viruses).
possible 1st viruses =
RNA viruses (not DNA viruses).
(Components of cells)
Perhaps some cellular components evolved abilities…
…to replicate themselves, independent of host cell control, and thus became parasites of those cells.
(Components of cells)
Potential candidates: (3)
- ) mRNA molecules
- ) DNA molecules such as plasmids
- ) transposons
(Intracellular Micro-organisms)
There is strong evidence that…
…the mitochondria and chloroplasts of eukaryotic cells are derived from prokaryotic cells.
(Intracellular Micro-organisms)
The parasite prokaryotic cells adopted…
…new modes of life within the cells of host organisms.
(Intracellular Micro-organisms)
Perhaps the evolutionary process continued further, leading to…
…greater degeneracy and loss of functions such as protein synthesis, until the intracellular intruder was no longer a cell or an organelle, but had become a virus.