Virsues Flashcards
What are the defining characteristics of viruses?
Obligate intracellular parasites; contain DNA or RNA (never both); lack ribosomes/mitochondria; <300 nm in size.
Why can’t viruses be grown on artificial media?
They require living host cells to replicate (lack metabolic machinery).
Compare helical vs. icosahedral symmetry in viruses.
-Helical (e.g., tobacco mosaic virus) has RNA coiled in protein tube
-Icosahedral (e.g., poliovirus) has 20 triangular faces made of capsomers.
What is the function of a viral envelope?
Derived from host membranes; contains viral glycoproteins for attachment/entry (e.g., HIV, influenza).
How does HIV’s structure differ from poliovirus?
HIV has an envelope + cone-shaped nucleocapsid
-Poliovirus is non-enveloped with icosahedral symmetry.
List the 5 key steps of viral replication.
Attachment → Penetration → Uncoating → Replication/Assembly → Release (budding or lysis).
What receptor does HIV use to enter T-cells?
CD4 + co-receptor (CCR5 or CXCR4).
Why does influenza virus require a virion transcriptase?
Its genome is negative-sense RNA (cannot directly act as mRNA).
How do poliovirus and HIV replicate their genomes differently?
Poliovirus uses viral RNA polymerase in cytoplasm; HIV uses reverse transcriptase (RNA→DNA) + integrates into host genome.
What is a cytopathic effect (CPE)? Give two examples.
Visible cell damage from infection (e.g., lysis by poliovirus; syncytium formation by HIV/measles).
How can viruses cause cancer?
Oncogenes (e.g., src in Rous sarcoma virus) disrupt cell cycle control → uncontrolled growth.
What makes influenza viruses prone to pandemics?
Segmented genome allows reassortment (antigenic shift) + high mutation rate (antigenic drift).
