Viral Genetics, Transduction, and Retroviruses (2B) - MCAT Biological and Biochemical Foundations of Living Systems

Temperate phage. Temperate phages can undergo lysogeny, integrating their genome into the bacterial host's DNA without immediate lysis.

Prophage. During lysogeny, the integrated phage DNA replicates passively with the host chromosome without producing virions.

Lytic cycle. In this cycle, the virus hijacks host machinery to replicate, assemble virions, and cause cell lysis for release.

Lysogenic cycle. This cycle allows viral DNA to integrate and replicate with the host genome, maintaining a dormant state without cell death.

Induction (prophage excision and entry into lytic replication). Environmental stressors trigger prophage excision, shifting from lysogeny to lytic replication and virion production.

Phage-mediated transfer of bacterial DNA between bacteria. Bacteriophages act as vectors, transferring bacterial DNA fragments from one bacterium to another during infection.

Random bacterial DNA packaged into phage during lytic infection. During lytic cycle assembly, phage particles mistakenly package host DNA fragments instead of viral genome.

Transfer of genes adjacent to prophage site after faulty excision. Faulty excision of prophage during induction incorporates nearby bacterial genes into the phage genome for transfer.

Generalized transduction. It involves random packaging of any host DNA segment into phage particles during lytic infection.

Specialized transduction. It occurs only with temperate phages, transferring specific genes flanking the prophage integration site.

Accidental packaging of host chromosomal DNA into phage capsid. In lytic infections, phage assembly errors lead to host DNA being encapsulated instead of viral DNA.

Imprecise prophage excision that carries adjacent bacterial genes. During induction, imprecise cutting of prophage from host DNA includes adjacent bacterial sequences.

Prophage-encoded trait that alters bacterial phenotype (often toxin). Integrated prophage genes express proteins that modify host traits, enhancing bacterial virulence or survival.

Negative-sense ssRNA viruses. Their genome cannot serve directly as mRNA, requiring polymerase to synthesize positive-sense RNA for translation.

Synthesizes DNA from an RNA template. Reverse transcriptase uses the viral RNA genome as a template to produce a complementary DNA strand.

cDNA (complementary DNA). Reverse transcriptase copies the retroviral RNA into a single-stranded DNA complement for integration.

Integrase. Integrase catalyzes the insertion of double-stranded viral DNA into the host chromosome during retroviral replication.

Provirus. The integrated DNA form of the retroviral genome persists in the host cell and serves as a template for transcription.

Host RNA polymerase II. The provirus integrates into the host genome, utilizing the host's transcriptional machinery for viral RNA production.

High mutation rate due to low proofreading fidelity. Reverse transcriptase lacks 3'-5' exonuclease activity, leading to error-prone replication and rapid evolution.

Budding through host membrane, acquiring a lipid bilayer envelope. Virions assemble at the plasma membrane and exit by budding, incorporating host-derived lipid envelope.

Viral surface proteins (capsid proteins or envelope glycoproteins). These proteins bind specific host cell receptors, dictating tropism and entry into susceptible cells.

Specialized transduction. This type relies on imprecise prophage excision, limiting transfer to genes near the integration site.

Generalized transduction. This type packages random host DNA fragments during lytic cycle, enabling transfer of diverse genes.