Viruses

Discussion on the nature of viruses and why they are not classified as living organisms.

1982: Richard Skrenta creates the Elk Cloner, the first infectious computer virus that spread between disks and computers.
Analogous to biological viruses, computer viruses require a host (computer) to spread. Without a host, they cannot exist.

Bacteriophages: These viruses inject DNA into bacteria, exploiting the host's cellular machinery to replicate.
Mechanism: Viral DNA is transcribed to mRNA, which is then translated into proteins. These proteins encapsulate new viral DNA for dispersion to infect other cells.
Conclusion: Like computer viruses, biological viruses cannot reproduce independently, which is why they are not classified as alive.

Viruses are significant because they are linked to various diseases.
Notable example: The 1918 influenza outbreak, which killed millions post-World War I.

Cellular Theory: Viruses may have originated from cellular remnants, such as plasmids.
Regressive Hypothesis: They might have evolved from once-independent cells that lost their ability to live autonomously (example: Chlamydia).
Co-evolution: Viruses evolved alongside cellular organisms, akin to mutual evolution seen in plants and insects.

All viruses contain nucleic acid, which can be either DNA or RNA, existing in various forms (single/double-stranded).
Protein Coat: Surrounds the virus, important for protection and infection.
Example: Tobacco mosaic virus, consisting of RNA coiled within protein subunits.
Envelope: Many viruses have a lipid bilayer surrounding them (example: Human Immunodeficiency Virus), facilitating easier entry into host cells when similar membranes fuse.

Definition: Involves the outbreak of virus replication and cell lysis (breaking open of the host cell).
Process: Virus injects DNA into the host bacterium → Host cell uses its machinery to produce viral DNA and proteins → Viruses erupt from the cell, beginning the cycle anew.
Exponential growth of virus: From a few viruses to billions through multiple cycles.

Definition: A stealthy replication method where viral DNA integrates into the host's genome.
Process: Viral DNA becomes part of the host's DNA → As the host reproduces, the viral DNA is copied without producing new viruses.
Example: Chickenpox virus integrates into the host's DNA and can re-emerge as shingles years later.

Viruses can switch between lytic and lysogenic cycles; for example, cold sores remain dormant until an immune response is weakened.

Final assessment: Viruses are not considered alive but play significant roles in numerous biological processes and diseases, making them crucial for study.