Virus Structure and Function Flashcards
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
