Particles Flashcards
What is a capsid
Viral shell made of redundant protein subunits that protects the genome
Blank + blank = virion
Genome + capsid
Why form a virion?
Genome exposure is risky
(physical damage from mechanical shearing, chemical from UV, enzymatic from nucleases)
What does a capsid do?
Protects the genome
Provides a surface for viral attachment proteins to bind host receptors
Hides genome from immune system until in right place
Capsid formation
Must be small subunits or viral genome would be too large
Self assemble
Virus Like Particles (VLPs)
No genome required, only one subunit gene
Ex- HPV vaccine
Helical capsids
Irregular subunits form a helix
Allows flexibility and resistance to shear forces
Most plant viruses are what type?
Helical and nonenveloped
All helical animal viruses have what?
An outer lipid envelope
How do capsids self assemble?
Electrostatic interactions (NAs are -, nucleocapsid/capsid is +, also N terminus is - and C terminus is +)
Hydrophobic interactions
Nucleocapsid
Protects and provides structure
Envelope
Stolen lipid membrane
Matrix proteins
Connects nucleocapsid and envelope
Envelope glycoproteins
Virus attachment proteins
Icosahedral (isometric) capsids
Irregular identical subunits with several shape options (commonly dodecahedron (12 pentagons) or icosahedral (20 triangles))
More triangles equal more stable
Naked viruses
Lyse cells when they exit
All plant viruses are what?
Naked
Pros of an enveloped virus
More efficient cell to cell transfer because envelope melts into host membrane
Doesn’t kill host cells
Cons of an enveloped virus
Envelope is more prone to damage which reduces attachment
Slower replication
Cell still has viral episodes so cell still can be identified as infected
Where is the budding assembly site?
The host plasma membrane normally (sometimes ER, golgi, or nuclear membranes)
Maturation during budding
The rearrangement of capsid, genome, and matrix proteins to facilitate infection
Can occur before or after release from the cell
Matrix proteins
Link nucleocapsid to the envelope
Glycoproteins
Anchor in envelope and do multiple things such as adhesion, enzymatic functions, and ion channels
