BIOA01H3 Lecture Notes - Lecture 23: Alpha Helix, Girus, Virus Classification
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The Tree of Life: Viruses Part 1
What are viruses?
- Microscopic infectious agents
- Contain DNA or RNA as genetic material
- Genome is surrounded by protein coat called capsid
- Some have an envelope – outer membranous layer containing glycoproteins
- Replicate solely when the nucleic acid has been delivered to a host cell
- Metabolically inert and use the host cells’ proteins and machinery to reproduce.
- Viruses infect all forms of life; every living organism has a virus that can infect it
- Estimate for how many viruses there are on the planet: 1031
- Each virus typically infects a few specific species = host range
- Within the hosts, only a limited number of cell types will be infected by the virus = tropism
Viruses = life?
- Viruses are on the boundary of what is considered “life” by biologists
- Contain genetic material; composed of protein capsids
- Cannot replicate and use this genetic information outside of a living host cell; host cell carries
out all steps for viral DNA or RNA → viral proteins
- Large viruses have been discovered that now possess many of the molecules needed for translation!
- E.g. Mimi virus
- Mimi virus = Giant virus
- Contain 7 of the 67 universal genes that are shared across the 3 domains of life.
- Encodes various proteins needed for translation and protein modification
- Translation factors, tRNAs, enzymes
- Can be “relics of a more complete ancestral protein-translation apparatus, gradually
lost through a genome reduction process”
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BIOA01H3 Full Course Notes
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Document Summary
Genome is surrounded by protein coat called capsid. Some have an envelope outer membranous layer containing glycoproteins. Replicate solely when the nucleic acid has been delivered to a host cell. Meta(cid:271)oli(cid:272)ally i(cid:374)ert a(cid:374)d use the host (cid:272)ells" protei(cid:374)s a(cid:374)d (cid:373)a(cid:272)hi(cid:374)ery to reproduce. Viruses infect all forms of life; every living organism has a virus that can infect it. Estimate for how many viruses there are on the planet: 1031. Each virus typically infects a few specific species = host range. Within the hosts, only a limited number of cell types will be infected by the virus = tropism. Viruses are on the boundary of what is (cid:272)o(cid:374)sidered (cid:862)life(cid:863) (cid:271)y (cid:271)iologists. Cannot replicate and use this genetic information outside of a living host cell; host cell carries out all steps for viral dna or rna viral proteins. Large viruses have been discovered that now possess many of the molecules needed for translation!
