A2.3 Viral Features, Diversity, and Life Cycles

Comprehensive vocabulary flashcards covering viral structure, diversity, life cycles (lytic and lysogenic), and rapid evolutionary mechanisms.

Viral Size Range

The small fixed size of viruses, typically measuring between $20$ and $300\,nm$, which allows them to invade host cells and evade the immune system.

Nucleic Acid

The genetic material of a virus, which can be single stranded or double stranded, and either linear or circular $DNA$ or $RNA$.

Capsid

A protein coat made up of repeating sub-units that encases and protects the viral genome.

Metabolic Processes in Viruses

Viruses cannot perform any metabolic processes and contain no organelles; they rely entirely on the host cell for energy, nutrition, and protein synthesis.

Positive Sense RNA

A type of viral genetic material that acts directly as $mRNA$.

Negative Sense RNA

A type of viral genetic material that requires transcription into $mRNA$ before translation.

Naked (Non-enveloped) Virus

A virus consisting only of a protein capsid, making it resistant to $pH$, heat, and detergents.

Enveloped Virus

A virus featuring a host-derived lipid bilayer with viral glycoproteins; it is easily destroyed by soap, alcohol, and drying.

Bacteriophage

A complex virus that infects $E.\,coli$ using a capsid head and a syringe-like tail structure for injecting double stranded $DNA$.

Retrovirus

A virus that infects human helper T-cells and uses the enzyme reverse transcriptase to produce $DNA$ from its $RNA$ genome.

Coronavirus

An enveloped virus that infects mammals and birds to cause respiratory disease, characterized by $RNA$ that acts as $mRNA$.

Lytic Cycle

A viral replication process where the virus hijacks host enzymes and ribosomes to produce new viruses, ending with the host cell bursting (lysis).

Lysogenic Cycle

A state of viral dormancy (lysogeny) where viral $DNA$ is integrated into or circulates within the host and is replicated alongside the host $DNA$ during cell division.

Viral Repressor Proteins

Proteins that keep most viral genes switched off during the lysogenic cycle to prevent cell bursting and maintain dormancy.

Obligate Parasitism

A survival form shared by all viruses where they are required to invade a host cell to replicate.

Antigenic Drift

The process of rapid mutation in influenza genes, caused by $RNA\,Polymerase$ lacking proofreading, leading to seasonal epidemics.

Reverse Transcriptase

An error-prone enzyme used by $HIV$ that creates a huge pool of genomic variants, allowing the virus to escape detection and evolve rapidly.