Course review
Review each learning objective in this topic, then open its concept explanation or question set.
Learning objective
• Viruses are non-cellular obligate parasites with fixed small size • Viral genome is either DNA or RNA, surrounded by a protein capsid • Viruses lack cytoplasm, ribosomes, and most metabolic enzymes
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Learning objective
• Viral genomes may be DNA or RNA, single- or double-stranded, linear, circular, or segmented • Capsids may be helical, polyhedral, conical, or complex • Viruses may be enveloped or non-enveloped; examples include TMV, HIV, coronavirus, and lambda phage
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Learning objective
• Lambda phage attaches to E. coli and injects double-stranded DNA • Viral DNA remains separate, host DNA is degraded, and host machinery makes viral parts • New phages assemble and are released by lysis of the host cell
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Learning objective
• Lambda phage DNA integrates into the E. coli chromosome as a prophage • The prophage replicates with the host genome during binary fission • Stress can induce prophage excision and entry into the lytic cycle
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Learning objective
• Viruses are likely polyphyletic, with several independent origins • Hypotheses include virus-first, escaped genes/progressive, and regressive/reduction models • Shared obligate parasitism may reflect convergent evolution
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Learning objective
• Viral evolution is driven by mutation, recombination, large population size, and short life cycles • RNA viruses often mutate rapidly because replication lacks proofreading • Influenza antigenic drift/shift and HIV reverse transcriptase errors affect vaccines and treatments
Start with the concept explanation, then practise to create mastery evidence.