Viral Genetics, Transduction, and Retroviruses (2B) - Bio & Biochem
- What is the term for integrated retroviral DNA within the host chromosome?
- Provirus. The integrated DNA form of the retroviral genome persists in the host cell and serves as a template for transcription.
- What is transduction in bacteria?
- Phage-mediated transfer of bacterial DNA between bacteria. Bacteriophages act as vectors, transferring bacterial DNA fragments from one bacterium to another during infection.
- Which viral genome types must bring or encode an RNA-dependent RNA polymerase?
- Negative-sense ssRNA viruses. Their genome cannot serve directly as mRNA, requiring polymerase to synthesize positive-sense RNA for translation.
- What is specialized transduction?
- 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.
- What is the enzyme that inserts retroviral DNA into the host genome?
- Integrase. Integrase catalyzes the insertion of double-stranded viral DNA into the host chromosome during retroviral replication.
- What is the term for the DNA copy of a retroviral genome made by reverse transcriptase?
- cDNA (complementary DNA). Reverse transcriptase copies the retroviral RNA into a single-stranded DNA complement for integration.
- What is the term for phage DNA integrated into a bacterial chromosome?
- Prophage. During lysogeny, the integrated phage DNA replicates passively with the host chromosome without producing virions.
- What is the key genetic consequence of reverse transcriptase for retroviruses?
- High mutation rate due to low proofreading fidelity. Reverse transcriptase lacks 3'-5' exonuclease activity, leading to error-prone replication and rapid evolution.
- Identify the key packaging error that causes generalized transduction.
- 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.
- What is the defining feature of a virus regarding replication machinery?
- Obligate intracellular parasite lacking independent replication machinery. Viruses require host cellular machinery for replication as they cannot independently synthesize proteins or generate energy.
- What is the term for a bacteriophage that can integrate into the host genome?
- Temperate phage. Temperate phages can undergo lysogeny, integrating their genome into the bacterial host's DNA without immediate lysis.
- Which host enzyme typically transcribes an integrated provirus into viral mRNA?
- Host RNA polymerase II. The provirus integrates into the host genome, utilizing the host's transcriptional machinery for viral RNA production.
- What is the viral life cycle called when viral DNA persists in the host without killing it?
- Lysogenic cycle. This cycle allows viral DNA to integrate and replicate with the host genome, maintaining a dormant state without cell death.
- Identify the key excision error that causes specialized transduction.
- Imprecise prophage excision that carries adjacent bacterial genes. During induction, imprecise cutting of prophage from host DNA includes adjacent bacterial sequences.
- Which envelope acquisition mechanism is typical for enveloped animal viruses?
- Budding through host membrane, acquiring a lipid bilayer envelope. Virions assemble at the plasma membrane and exit by budding, incorporating host-derived lipid envelope.
- Identify the most likely transduction type if only genes near an attachment site transfer.
- Specialized transduction. This type relies on imprecise prophage excision, limiting transfer to genes near the integration site.
- Which transduction type can transfer any bacterial gene: generalized or specialized?
- Generalized transduction. It involves random packaging of any host DNA segment into phage particles during lytic infection.
- Which transduction type is limited to genes near the prophage insertion site?
- Specialized transduction. It occurs only with temperate phages, transferring specific genes flanking the prophage integration site.
- Which event converts a prophage from lysogeny to the lytic cycle?
- Induction (prophage excision and entry into lytic replication). Environmental stressors trigger prophage excision, shifting from lysogeny to lytic replication and virion production.
- Identify the most likely transduction type if many different host genes transfer randomly.
- Generalized transduction. This type packages random host DNA fragments during lytic cycle, enabling transfer of diverse genes.
- What is lysogenic conversion?
- Prophage-encoded trait that alters bacterial phenotype (often toxin). Integrated prophage genes express proteins that modify host traits, enhancing bacterial virulence or survival.
- Which viral structural component primarily determines host cell attachment specificity?
- Viral surface proteins (capsid proteins or envelope glycoproteins). These proteins bind specific host cell receptors, dictating tropism and entry into susceptible cells.
- What is generalized transduction?
- Random bacterial DNA packaged into phage during lytic infection. During lytic cycle assembly, phage particles mistakenly package host DNA fragments instead of viral genome.
- What is the immediate role of reverse transcriptase in retroviruses?
- Synthesizes DNA from an RNA template. Reverse transcriptase uses the viral RNA genome as a template to produce a complementary DNA strand.
- What is the viral life cycle called when virions are produced and the host cell lyses?
- Lytic cycle. In this cycle, the virus hijacks host machinery to replicate, assemble virions, and cause cell lysis for release.