Viruses: Borrowed Life

Study Notes

Nature of Viruses

Viruses lack metabolic processes and cannot reproduce independently, relying on host organisms (animals, plants, bacteria) for replication.
Considered as "programs" that integrate into host genomes, similar to computer viruses.
Antibiotics are ineffective against viruses due to their lack of metabolism; intervention focuses on viral interactions with host cells.

Types of Viruses

Two main categories: enveloped viruses and naked viruses.
Naked viruses have a protective protein coat called a capsid while enveloped viruses derive their lipid-protein envelope from host cell membranes.
Viruses require only nucleic acid and a host cell for reproduction; some may carry replication enzymes like reverse transcriptase found in retroviruses.

Viral Reproduction Processes

Viruses reproduce primarily through two cycles:
- Lytic cycle: Virus destroys host cell upon release.
- Nonlytic cycle: Enveloped viruses bud off from host cells, allowing gradual release.
All viruses contain single-stranded RNA or double-stranded DNA, categorized based on their nucleic acid type and host specificity.

RNA and DNA Viruses

Notable RNA viruses include:
- HIV (AIDS virus)
- Influenza and measles viruses
- Tobacco mosaic virus (TMV)
- Picornavirus group viruses (e.g., poliovirus, rhinovirus)
- Ebola virus and coronaviruses like SARS, causing respiratory concerns.
Key DNA viruses encompass:
- Papovaviruses, which can lead to warts and tumors.
- Variola (smallpox) and Vaccinia (cowpox) viruses.
- Herpes viruses, adenoviruses, bacteriophages (bacterial viruses), and baculoviruses (insect-specific viruses).

Mechanism of Viral Infection

Viruses initiate infection by attaching to host cell surfaces.
DNA viruses like bacteriophages inject their genetic material into bacterial cells, leveraging bacterial enzymes for synthesizing new viral components.
In animal cells, the viral envelope fuses with the cell membrane, facilitating the entry of the viral genome.
Retroviruses convert their RNA into DNA via reverse transcriptase, which is integrated into the host's chromosomal DNA, enabling further viral replication.

Consequences of Viral Infection

Infected cells produce viral proteins and RNA, contributing to disease pathogenesis; some viral DNA remains dormant within host DNA, potentially being activated in future generations.

Description

Explore the fascinating world of viruses that challenge the criteria of living organisms. This quiz examines their unique reproductive mechanisms and the implications of their existence as molecular parasites. Test your understanding of how viruses interact with their hosts.