All flashcards
Flashcard 1: What is a prophage?
Answer: Integrated bacteriophage genome within a bacterial chromosome. The prophage replicates passively with the bacterial DNA, enabling lysogenic cycles in bacteriophages.
Flashcard 2: What is the term for virus binding to specific host cell surface molecules?
Answer: Attachment (adsorption) to host receptors. Specific binding to host receptors initiates infection by facilitating viral entry into susceptible cells.
Flashcard 3: What is the correct order of the general viral life cycle steps after attachment begins?
Answer: Entry, uncoating, replication, assembly, release. This sequence follows attachment, enabling genome delivery, replication using host systems, virion formation, and exit from the cell.
Flashcard 4: What is uncoating in a viral life cycle?
Answer: Removal of the capsid to release the viral genome. This process exposes the viral nucleic acid, allowing access to host machinery for transcription and replication.
Flashcard 5: Which option best distinguishes lytic from lysogenic infection?
Answer: Lytic kills quickly; lysogenic integrates and can remain latent. Lytic cycles lead to rapid replication and host cell death, while lysogenic cycles involve genome integration for potential dormancy.
Flashcard 6: What is a provirus?
Answer: Viral genome integrated into a eukaryotic host genome. This integration allows latent infection in eukaryotic cells, as seen in retroviruses like HIV.
Flashcard 7: Identify the enzyme required for retroviruses to convert RNA into DNA.
Answer: Reverse transcriptase (RNA-dependent DNA polymerase). This enzyme synthesizes complementary DNA from the viral RNA template, a key step in retroviral replication.
Flashcard 8: What is the role of integrase in retroviral replication?
Answer: Insertion of viral DNA into the host genome. Integrase catalyzes the covalent insertion of viral cDNA into the host chromosome, forming a stable provirus.
Flashcard 9: Which option correctly matches Baltimore Class I with its genome type?
Answer: Class I: double-stranded DNA (dsDNA). Baltimore Class I viruses, like herpesviruses, use dsDNA genomes that can be transcribed by host polymerases.
Flashcard 10: Which option correctly matches Baltimore Class II with its genome type?
Answer: Class II: single-stranded DNA (ssDNA). Baltimore Class II viruses, such as parvoviruses, replicate via ssDNA that is converted to dsDNA in the host nucleus.
Flashcard 11: Which option correctly matches Baltimore Class III with its genome type?
Answer: Class III: double-stranded RNA (dsRNA). Baltimore Class III viruses, like reoviruses, use dsRNA genomes requiring viral polymerase for mRNA synthesis.
Flashcard 12: Which option correctly matches Baltimore Class IV with its genome type?
Answer: Class IV: positive-sense single-stranded RNA (+ssRNA). Baltimore Class IV viruses, such as picornaviruses, have +ssRNA genomes that function directly as mRNA.
Flashcard 13: Which option correctly matches Baltimore Class V with its genome type?
Answer: Class V: negative-sense single-stranded RNA (-ssRNA). Baltimore Class V viruses, like orthomyxoviruses, require viral RdRp to transcribe -ssRNA into mRNA.
Flashcard 14: Which option correctly matches Baltimore Class VI with its genome type?
Answer: Class VI: +ssRNA with reverse transcription (retroviruses). Baltimore Class VI viruses, including retroviruses, use reverse transcription to convert +ssRNA to DNA for integration.
Flashcard 15: Which option correctly matches Baltimore Class VII with its genome type?
Answer: Class VII: dsDNA with reverse transcription (pararetroviruses). Baltimore Class VII viruses, such as hepadnaviruses, employ reverse transcription during replication of their dsDNA genomes.
Flashcard 16: What is the key functional difference between +ssRNA and -ssRNA viral genomes at entry?
Answer: +ssRNA is mRNA; -ssRNA must be transcribed first. Positive-sense RNA can be directly translated by host ribosomes, whereas negative-sense requires prior transcription to mRNA.
Flashcard 17: Which viral genome types must carry an RNA-dependent RNA polymerase in the virion?
Answer: -ssRNA and dsRNA viruses. Host cells lack RNA-dependent RNA polymerase, so these viruses must package it to transcribe their genomes upon entry.
Flashcard 18: Identify the immediate translation outcome when a +ssRNA virus enters the cytosol.
Answer: Host ribosomes translate the genome directly into protein. The +ssRNA genome acts as mRNA, enabling immediate synthesis of viral proteins by host translational machinery.
Flashcard 19: What is the most typical release mechanism for enveloped viruses?
Answer: Budding through a host membrane. Budding allows acquisition of the lipid envelope from host membranes while often preserving host cell integrity.
Flashcard 20: What is the most typical release mechanism for nonenveloped viruses?
Answer: Host cell lysis. Accumulation of virions inside the cell leads to membrane rupture, releasing nonenveloped viruses into the environment.
Flashcard 21: Which option best describes why enveloped viruses are generally less stable in the environment?
Answer: Their lipid envelope is disrupted by detergents and desiccation. The lipid bilayer is susceptible to environmental factors that disrupt membrane integrity, inactivating the virus.
Flashcard 22: Identify the correct conclusion: a virus has -ssRNA and lacks RNA polymerase in the virion.
Answer: It cannot initiate infection; it must package RNA-dependent RNA polymerase. Negative-sense ssRNA requires transcription to mRNA by RdRp, which must be virion-packaged since hosts lack this enzyme.
Flashcard 23: Identify the correct conclusion: a viral genome integrates into host DNA without immediate lysis.
Answer: This is a lysogenic/latent strategy (provirus or prophage). This integration enables latent persistence and replication with host DNA without causing immediate cell death.
Flashcard 24: What is the defining feature that makes a virus an obligate intracellular parasite?
Answer: It must use host ribosomes and metabolism to replicate. Viruses lack their own translational and metabolic machinery, necessitating host cell resources for genome replication and protein synthesis.
Flashcard 25: Which viral structure primarily determines host cell tropism by binding receptors?
Answer: Capsid proteins or envelope glycoprotein spikes. These proteins recognize and interact with host cell receptors, conferring specificity for cell types and species.