Structure and Composition of Viruses Flashcards
What is the smallest virus at 17nm?
Porcine circovirus type 1
What is the largest virus of animals at 200nm x 300nm?
Poxvirus
Viruses can have what shapes?
Filament (Ebola) Bullet (Rabies) Tadpole (bacteriophages) Rod (Tobacco Mosaic) Brick (Poxvirus) Spherical (Rotavirus)
What is it called when a virus can change its shape or size?
Pleomorphism
What are the 4 common ways to determine the morphology of a virus?
Electron microscopy
Cryo-electron microscopy
X-ray crystallography
NMR
The protein shell that encases the viral nucleic acid:
Capsid
Building blocks of the capsid:
Capsomeres held together by non-covalent bonds
Which type of viruses have a double-layered capsid?
Reoviruses
What makes up the nucleocapsid?
Capsid + viral nucleic acid
Types of viral morphology/shapes:
Helical: in animal viruses are enveloped, but can be naked in plant viruses ie tobacco mosaic.
Cubic/Icosahedral: seen in spherical viruses, can be naked or enveloped.
Complex: composed of several parts with separate shapes/symmetries. (Poxvirus and bacteriophages)
What is the triangulation number for icosahedral viruses?
T = h^2 + (h x k) +k^2
What does the triangulation number determine?
Relation between the number of pentagons and hexagons of the icosahedron.
In an icosahedral virus, which capsomeres makes up the vertices and which make up the facets?
Pentons make up vertices
Hexons make up facets
What is the simplest icosahedron, with a triangulation number of 1 and a capsid containing 60 copies of CP protein?
Parvovirus
What are the triangulation numbers for the inner and outer capsids of Reoviridae?
Inner: T=2
Outer T=13
What are the functions of the capsid?
Structural symmetry
Protection of viral nucleic acid from enzymes, chemicals, and pH/Temp
Attachment to host cells
Interaction with host cell membrane to form envelope
Uncoating of the viral genome in host cell
Transporting viral genome to correct site
Packaging of nucleic acid genome
Determines antigenicity of virus (contains antigenic sites)
The ______ is a lipid bilayer with embedded proteins.
Envelope
How is the envelope formed?
Budding of the nucleocapsid through a cellular membrane (cytoplasmic, golgi, or nuclear).
What are the 2 types of proteins found in the viral envelope?
Glycoproteins (spikes) and matrix proteins
What are the 2 types of glycoproteins in the viral envelope?
External: major antigens
Channel: hydrophobic, form a channel through the envelope.
Major functions of external glycoproteins in the viral envelope.
Antigenicity, hemagglutination, receptor binding, membrane fusion
Major functions of channel glycoproteins in the viral envelope.
Alters permeability of the membrane (ion channels). Modify internal environment of the virus.
Functions of matrix proteins in the viral envelope.
Link nucleocapsid to envelope
Virus assembly
Stabilize envelope
*recognition site of the nucleocapsid at the plasma membrane and mediates encapsidation of nucleocapsid into the membrane envelope
Limiting environments for the viral envelope:
Dry, hot, change in pH
*maintained only in aqueous or moist env
Products that can inactivate enveloped viruses by dissolving the lipid membrane:
Ether
Chloroform
Sodium deoxycholate, detergents
Which are easier to sterilize and survive shorter periods in the environment, naked or enveloped viruses?
enveloped
T/F: the viral nucleic acid can be double- or single-stranded DNA, or double- or single-stranded RNA?
TRUE
Mechanisms of genetic diversity in viruses:
Antigenic drift
Antigenic shift
_______ _____ leads to point mutations (silent, missense, nonsense) that normally cause minor changes, but may induce resistance to antiviral drugs and vaccines.
Antigenic drift
_______ _____ is the recombination, or exchange of nucleotide sequences between related viruses during replication.
Antigenic shift
What is the most important mechanism for high genetic diversity in viruses with segmented genomes?
Reassortment
What type of antigenic shift occurs in viruses with a single gene segment?
Recombination
Retroviral integrase is a viral enzyme responsible for:
enabling viral genetic material to be integrated into the DNA of the infected cell. (HIV)
Reverse transcriptase is a viral enzyme responsible for:
generating complementary DNA from an RNA template.
Nucleic acid polymerases are responsible for:
viral genome replication
What type of viral proteins play a role WITHIN the infected cell during virus replication, or regulate virus replication/assembly.
Nonstructural proteins
An incomplete virion is missing:
Nucleic acid. (empty capsid)
A defective virion cannot replicate because it lacks:
A full complement/copy of viral genes.
*can result from mutations or errors in production or assembly of virions
A ________ contains nonviral genome within the capsid.
Pseudovirion
Virus pseudotypes occur when:
related viruses infect the same cell and the genome of one virus is enclosed in the capsid of another virus.
