Key Terms
Size range
Most virions are 20 to 250 nm in diameter. Some giant amoeba-infecting viruses reach 1000 nm.
Every virion has
Nucleic acid genome + capsid. Some also have an envelope.
Example
Lambda (lambda) phage infecting E. coli.
DNA virus diseases
Chickenpox, hepatitis B, herpes, HPV (linked to cervical cancer). RNA virus diseases: influenza, hepatitis C, measles, r
Six steps apply to most viruses
Attachment, Penetration (Entry), Uncoating, Replication, Assembly, Release (Egress).
ENTRY (Penetration) Bacteriophages
Inject nucleic acid only; capsid stays outside. Plant/animal viruses: enter by endocytosis (whole virus engulfed) OR by
DNA viruses
Generally use host enzymes to replicate DNA and transcribe mRNA. RNA viruses: use their own RNA-dependent RNA polymerase
Most plant viruses
Single-stranded (+)RNA genomes. Plant viruses cannot breach the cell wall actively; mechanical damage is required for en
Economic impact
Plant viruses cause significant annual losses in food crops and ornamental plants worldwide.
Non-enveloped entry options
1. Receptor-mediated endocytosis: virus is engulfed in a vesicle 2.
Enveloped entry options
1. Receptor-mediated endocytosis 2.
Purpose
Stimulate protective immunity without causing major disease. The immune response generated prevents or limits future inf
Three vaccine types
1. Live attenuated: weakened virus; still infects, grows poorly, triggers immunity.
Attenuation process
Grow wild-type virus in non-standard lab conditions (different cells, different temperatures). The virus accumulates mut
Post-exposure vaccination
Works for rabies and Ebola because disease progression is slow enough that a boosted immune response can prevent the vir