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Learn about viruses, non-living entities that invade cells, replicate using host metabolism, and evolve alongside hosts. Explore viral reproduction stages like attachment, entry, replication, assembly, and release.
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Bio 2201 Unit 2 – Biodiversity - Virus
A Virus Viruses are NOT organisms: • They do not have cellular structure and are not classified into the six kingdoms • They are successful at invading the cells of organisms • They can only reproduce using the metabolism (energy) of the host cell • They consist of strand of DNA/RNA • Surrounded by a protective protein called a capsid • Viruses have a variety of shapes • These shapes are determined by the type and arrangement of proteins in the capsid.
A virus • Cannot replicate without a host • Origin is thought to be fragments of nucleic acid which had escaped from their original cell • Survives by becoming a parasite on specific hosts. • This suggests that viruses and their hosts probably evolved together • This would make a virus and a host more closely related than a particular virus with other viruses
Example of Viral Reproduction • Attachment: • The T4 phage is a complex virus that attaches to a specific receptor site on a host's cell wall (eg. E. coli). Weak chemical bonds form between the attachment and receptor sites adhering (sticking to) the virus to the host
2. Entry (Penetration) : T4 injects it nucleic acid (DNA) into the host cell. The viral DNA passes through the core and into the cell. The capsid remains outside. 3. Replication: The host protein synthesis is stopped by viral degradation of host DNA. The host’s metabolism will replicate the viral DNA (or RNA)
4. Assembly: Spontaneous assembly of new virus particles occurs. 5. Lysis and Release: The host cell plasma membrane and cell wall lyses (breaks open) releasing the new virus particles. The host cell dies.
