(Final) Virus structure Flashcards
What is the smallest virus of animals?
Porcine circovirus type 1
What is the largest virus of animals?
Pox virus
What shape is the rabies virus?
bullet shape
What shape is the pox virus?
Brick shape
What does it mean if a virus is pleomorphic?
It has the ability to alter their shape or size
What is a bacteriophage?
Tadpole shaped virus that infects bacteria
What kind of microscope is used to see viruses? What kind of staining is commonly used?
Transmission Electron microscope
negative staining
What is cryo-electron microscopy?
Liquid nitrogen is used to freeze the sample, allowing it to be observed in their native environment
*finer resolution/clearer image with sample intact
Besides electron microscopy, what are two other method to dectect/visualize viruses?
E-ray crystallographic method
*even more detailed image
Nuclear magnetic resonance method
What is the basic structure of a virus?
DNA or RNA wrapped in a capsid (protein coat) - wrapped in an envelope (bubble of fat)
The envelope can have glycoprotein spikes
What are the two types of capsid symmetry?
Polyhedral
Helical virus
T/F: Animal viruses that have capsids with a helical symmetry are most often enveloped
TRUE
*but there can be naked viruses of PLANTS that have a helical symmetry
Most viruses have one capsid, what is the virus that is an exception with a double layered capsid?
Reoviruses
What is the basic subunit protein in the capside of a virus?
A capsomere
Capsid + virus DNA or RNA = _________
Nucleocapsid
What are the components of the icosahedral capsid?
12 pentons (12 corners) **always constant** 20 facets (Hexons - this numer will vary) 30 edges
What is the triangulation number of a virus?
It denotes the relationship between the number of pentagons and hexagons of the icosahedron
T= (h^2 + h)(k +k^2)
h and k are directions
T/F: the number of pentons is ALWAYS constant (12)
TRUE
What virus has the simplest icosahedron, with a T=1, triangulation number?
Parvovirus
The capsid consists of 60 copies of CP proteins
What virus has a more complex symmetry with an outer capsid that has T=13 icosahedral symmetry, and inner capsid that has a T=2 icosahedral symmetry?
REOVIRIDAE
**only viruses with 2 capsids
What is the symmetry of the pox virus?
It is very COMPLEX - so it is neither icosahedral or helical
What are the functions of the viral capsid?
- structural symmetry
- Encases and protects the viral nucleic acid from enzymes, chemicals, and physical conditions
- functions in attaching to the host cell (receptor proteins)
- Once inside the host hell - it helps deliver the nucleic acid to the replication site
- functions in packaging of newly replicated virus
T/F: Viral capsids have antigenic proteins
TRUE
these can be targeted for tx or vaccines
What is a viral envelope composed of? What is the fuction?
Lipid bilayer with embedded proteins
Facilitaes virus entry into the host cell and may help the virus to adapt fast and evade the host immune system
Where does the viral envelope come from?
It is stolen from the host cell:
From the nuclear membrane, cytoplasmic membrane, golgi membrane, or ER membrane
What are the two viral proteins primarily found in the envelope?
Glycoprotein (spikes)
Matrix protein
What envelope proteins are highly antigenic, and involved in functions such as hemagglutination, receptor binding, and membrane fusion?
External glycoproteins
The spikes do everything
What proteins in the envelope, regulate the influx and efflux of ions into the virus; maintaining the proper internal pH?
Channel proteins
T/F: Some viruses have additional Fusion proteins within/on the lipid envelope
TRUE
helps the viral envelope fuse with the host cell
What is the function of envelope matrix proteins?
Plays a crucial role in virus assembly. Attaches to the inside of the host cell - where glycoproteins are along the outside, to act as indicators for newly replicated viral DNA/RNA to find the glycoproteins
*also stabilize the lipid envelope
T/F: Virus envelopes help viruses survive better in the environment
FALSE
enveloped viruses are LESS stable than naked viruses
T/F: the viral matrix protein is located between the viral nucleic acid and the capsid.
FALSE
It is located between the capsid and the envelope
Which one of the following is NOT a component of viruses?
Nucleic acid
Capsid
Capsule
Envelope
Capsule
T/F: Viral DNA is always circular
False
Can be linear as well
What sense RNA is directly translated and used to synthesize viral protein?
Positive sense
Negative sense must first be converted to positive sense RNA
What variations of viral RNA can you have in viruses?
single stranded vs double stranded
positive sense vs negative sense
segmented vs non segmented
What are some mechanisms of genetic diversity that viruses may undergo?
Antigenic drift = point mutations
(can influence the dx, vaccines etc)
Antigenic shift:
Recombination = Mixture of two different viruses - making a new one
(**occurs in viruses with a SINGLE gene segement)
Reassortment = (**ocurrs in viruses with multiple segements) Swapping of genome segments between viruses
shift will result in a drastic change in the antigenicity of the virus
Which one of the following is NOT a mechanism of genetic diversity of viruses?
Reassortment
Point mutations
Recombination
Conjugation
Conjugation
What are some important viral enzymes that are critical to infection, and their functions?
- Retroviral integrase (IN) - enzyme produced by a retrovirus hat enables its genetic material to be intergrated into the DNA of the infected cell
- Reverse transcriptase (RT): enzyme used to generate complementary DNA (cDNA) from a RNA template
- Nucleic acid polymerases: Viral genome replication
What is the function of viral nonstructural proteins?
May play roles within the infected cell during virus replication
or act in regulation of virus replication or virus assembly
T/F: Nonstructural proteins are seen in extracellular virions
FALSE
These only appear when the virus is replicating in the host cell
What is missing, that makes a virion incomplete?
No nucleic acid
Just an empty capsid
What makes a virion defective?
If it cannot replicate because:
It lacks a full complement or copy of viral genes
Due to:
mutations or errors in the production or the assembly of viruses
What is a pseudovirion?
A viral capsid with a NON-viral genome inside
