Physical structures of Virus

An aggregate of many molecules often of different nature

(svedberg)-value is a value derived from the sedimentation rate of particles and molecules in the ultracentrifuge

10^-13 seconds

-Protein subunit
-Structural subunit
-morphological unit
-capsid
-nucleocapsid
-Envelope (not all viruses have these)
-Virion

individual folded protein molecules

unit from which capsid of nucleocapsid are build, may comprise one protein subunit or multiple different subunits

surface structure seen by electron microscopy (knobs, projections, clusters, etc.)

regular, shell-like structure composed of aggregated protein subunits which surrounds the viral nucleic acid.

viral nucleic acid enclosed by a capsid protein coat.

lipid bylayer containing viral glycoproteins. the phospholipids in bylayer are derived from the cell that the virus arose from. Not all viruses have envelopes

physical virus particle. nucleocapsid alone for some viruses or includes outer envelope structure for others.

-protect genome from atmosphere
-Virus-attachment protein-interacts w/ cellular receptor to initiate infection. made up of repeat subunits in case there is damage to some it will not prevent infection due to many receptor sites.
-delivery of genome in infectious form. May simply dump genome into cytoplasm (most +ssRNA viruses) or serve as the core for replication (retroviruses and rotaviruses)

-info is encoded in components themselves (nucleic acids and proteins). some proteins can form capsid shells in absence of genome while others form around genome.
-assembly is driven by non-covalent bonds (protein-protein, protein-nucleic acid, protein-lipid).

Not enough genomic information: a genome can only produce proteins 15% of its molecular weight so need multiple proteins to encapsidate it.

Helical (rodlike, DNA shape), Icosohedral (spherical), and irregular (least common)

energetically favorable
-allow flexibility
-most helixes are formed by a single major protein arranged w/ a constant relationship to each other
-most phage and plant viruses in this shape are enveloped while not all animal viruses are

-12 vertices, 20 triangular faces, 30 edges.
-have 5-(pass through vertices), 3-(pass through centers of traingular faces), and 2-(pass through edges)fold rotational axes.
-triangulation numbers (T, which are protein subunits on one side of triangle) equal to 1, 3, 4, 7, 9, 16, and 25

viruses that are too large and have evolved to have a shape more "cell like"

-produce large amounts of viral genome and inhibit cell mRNA
-viral genomes have packaging signals (psi) that form structures recognized by one of the capsid proteins

nonenveloped-generally form in cytoplasm and mature before lysing from cell

enveloped viruses generally form capsid as they bud from envelope.
- envelope proteins are inserted into host cell membrane prior to budding
-often virion matures after release (budding)