Virus Structure and Function Flashcards
(14 cards)
What are capsids?
highly conserved structural motif. protect and help deliver genome. Surrounded by lipid envelope
What are the two types of capsids?
Helical capsids - rotational symmetry, form a disk
Icosahedral - 20 triangular faces with 2,3,5 fold axis of symmetry
What are the classes of viruses
dsDNA gapped circular dsDNA ssDNA dsRNA ss(+) RNA ss(-) RNA ss(+) RNA w/ DNA intermediate
dsDNA viruses
mRNA made using – DNA strand as template using a host RNA Pol II. Genome replication can happen using host DNA polymerase too
gapped circular dsDNA
mix of ssDNA and dsDNA. mRNA transcribed using – DNA strand as template using a host RNA Pol II. Can then use reverse transcriptase to replicate genome from the produced mRNAs.
ssDNA viruses
mRNA transcribed using – DNA strand as template using host RNA Pol II. Genome is replicated by using a dsDNA intermediate to serve as a template.
dsRNA viruses
These viruses have to have RdRp in their capsid to transcribe mRNA off the genome. RdRp also helps with actual genome replication.
ss(+)RNA
Translated directly into protein by cellular ribosomes (genome is ‘ribosome ready’). mRNA production via RdRp. Upon infection → ssRNA converted to dsDNA by reverse transcriptase. dsDNA incorporates into host genome → creates a provirus.
ss9-) RNA
first copied into + strand mRNA by RdRp. Genome is also replicated by RdRp.
ss(+)RNA w/ DNA intermediate
virus copies ssRNA into dsDNA with reverse transcriptase → integrates into host cell → mRNA transcribed using host’s RNA Pol II. Genome replicated with help of RdRp.
Describe general replication cycle of a virus
Eclipse period - when virus particles have broken down, no virus is detectable in or outside of cell
Latent period - time it takes from start of infection to the release of new virus particles
Packing - assembly of new viran genome
Egress - release!
What occurs during the latent period?
Attachment of virus to a receptor (targets are proteins/carbs, carbs less specific.)
Entry - naked virus endocytosed. Enveloped ciruses fuse w/ host membrane (requires fusion protein)
Both uncoated so the genome is exposed.
Gene expression - DNA viruses, - strand used as template, all gaps must be filled, use host RNA Pol II in the nucleus. (Poxvirus replication in cytoplasm)
In RNA viruses - RdRp helps produce mRNA and replicate RNA genomes.
Descripe what occurs during virus packing
- icosahedral → capsid either assembles around the viral genome, or the genome is fed into the capsid.
- helical → viral genome is coated with nucleocapsid protein during synthesis.
- packing generally causes a cytopathic effect and can be demonstrated as cytoplasmic/nuclear inclusions
Describe what happens during egress
- naked capsids released by lysis
- enveloped viruses bud either directly from the plasma membrane, or from the Golgi/ER
