Chapter 13: Viruses - Shape, naming, and multiplication of animal viruses Flashcards
What is the polyhedral shape of viruses? (2)`
- usually icosahedral
- shape with 20 triangular faces
What is the helical shape? (2)
- long rods
- can be rigid or flexible
What is the shape of an enveloped virus? (2)
- roughly spherical
- dictated by lipid bilayer
What is the complex shape of viruses? (2)
- polyhedral head with a helical tail
- only found in bacteriophages
In lecture, what is the most common entity in the world?
bacteriophages
What are 3 factors that classify viruses?
- Nucleic acid type (DNA or RNA, single or double strand, segmented or single)
- capsid structure
- presence of envelope (none = naked)
How does capsid structure help classify viruses?
they can either be polyhedral or helical
How do we name viruses?
- Family - ends with suffix - viridae
- genus - ends with suffix - virus
- species - specific epithets are not used
What are 6 ways that animal viruses multiply? (6)
- Adsorption
- Penetration
- Uncoating
- Biosynthesis
- Maturation and assembly
- release
What is adsorption? (2)
- attachment to host cell
- viruses have attachment sites that recognize protein or glycoprotein of host
What is penetration? (3)
- entry into host cell
- Most enveloped viruses enter by fusion
- naked virus enters the cell via endocytosis
Since fusion occurs in penetration, what does it mean?
- lipids of envelope fuse with host cytoplasmic membrane
What occurs in uncoating?
- viral nucleic acid is freed from the capsid
What occurs in biosynthesis? (4)
- viral nucleic acids are replicated
- DNA replicated -> nucleus
- RNA replicated -> cytoplasm
- viral proteins (capsomeres) are synthesized in the cytoplasm
What does biosynthesis rely on?
- host metabolic machinery
ex. replication and transcription enzymes, ribosomes
What occurs in maturation and assembly? (3)
- New virions are assembled
- capsomeres form the capsid
- nucleic acid enters capsid, forming the nucleocapsid
In lecture, where do capsomeres form capsids?
in cytoplasm of infected cell
What occurs in release for naked viruses? (2)
- naked viruses burst out and rupture host cells
- host cell dies
What occurs in release for enveloped viruses? (3)
- bud out as virus pushes through cytoplasmic membrane
- steady release of mature viruses
- host cell stays alive for a long time
