Structure & Chemical Composition of Viruses Flashcards
What is the smallest virus?
Porcine circovirus type 1
What is the largest virus?
Poxvirus
What shape is the ebola virus?
Filament-shaped
What shape is the rabies virus?
Bullet-shaped
What shape is the bacteriophage?
Tadpole-shaped
What shape is the tobacco mosaic virus?
Rod-shaped
What shape is the poxvirus?
Brick-shaped
What shape is the rotavirus?
Spherical
What is pleomorphism?
Ability of some viruses to alter their shape or size?
What are 4 common methods to determine the morphology of viruses?
- Electron microscopy (EM)
- Cyro-electron microscopy (Cryo-EM)
- X-ray crystallographic method
- Nuclear magnetic resonance (NMR)
What are 4 important characteristics of virus morphology?
- DNA or RNA genes
- Capsid
- Envelope, a bubble of fat
- Molecules of protein
What is a capsid?
Protein shell of a virus that encases/envelopes viral nucleic acid or genome
Basic subunit protein in virus capsid
What is a capsid made of?
Capsomeres
Most viruses have one capsid, except?
Reoviruses
What makes up a nucleocapsid?
Capsid + Virus Nucleic acid/Genome
In all animal viruses, the helical nucleocapsid is enclosed with what kind of envelope?
Lipoprotein envelope
What kind of nucleocapsid does a plant virus have?
Naked helical nucleocapsid
What two types of capsomeres are present in a icosahedral capsid?
- Pentagonal capsomeres (pentons)/(always 12 pentons
2. Hexagonal capsomeres (hexons)
What is the triangulation number (T-number)
T = h2 + h * k + k2
Relationship between penton (constant) and Hexon (variable)
What are two types of icosahedrals?
- Naked
2. Enveloped
What is the simplest icosahedron? (T=1)
Parvovirus (capsid consists of 60 copies of CP protein)
What kind of Icosahedral symmetry does Reoviridae have?
Outer capsid has T=13, inner capsid has T=2
What kind of symmetry does poxvirus have?
Complex symmetry
T/F: A viral capsid is responsible for structural symmetry of virus particle
True
What is the importance of receptor attachment proteins on viral capsid?
Facilitate the attachment of virus to specific receptors on susceptible host cells
The viral capsid interacts with host cell membrane to form the ___________
Envelope
What is responsible of uncoating the genome in host cell?
The viral capsid
The viral capsid transports the which genome to the appropriate site
Viral genome
The viral capsid facilitates __________ of nucleic acid genome
Packaging
The viral capsid contains antigenic sites that determine the __________ of the virus
Antigenicity
What is the envelope of an enveloped virus made of?
Lipid bilayer with embedded proteins
How does a virus acquire the envelope?
Via budding of viral nucleocapsid through a cellular membrane such as cytoplasmic membrane, golgi membrane or nucleus membrane
What are the two proteins primarily found in virus envelope?
- Glycoprotein
2. Matrix protein
What are the two types of glycoproteins in virus envelope?
- External glycoprotein
2. Channel proteins
The external glycoproteins are the major (Antigens or antibodies?) of the virus
Antigens
What are the functions of external glycoproteins?
Hemagglutination, receptor binding, antigenicity, and membrane fusion
What are channel proteins?
Mostly hydrophobic proteins that form a protein lined channel
What is an important virus envelope glycoprotein?
Fusion (F)
What are the important functions of a virus envelope matrix protein?
- Role in virus assembly
- Stabilization of lipid envelope
- Recognition site of nucleocapsid
- Mediates encapsidation of RNA-nucleoprotein cores in to membrane envelope
How is the lipid bi-layer in virus envelope acquired?
Acquired from a cellular membrane of host cell, such as nuclear membrane, ER membrane, etc.
How is the lipid bi-layer in virus envelope maintained?
In aqueous or moist environment
T/F: Enveloped viruses are easier to sterilize than non-enveloped viruses and cannot survive for longer periods in environment
True
Where is the matrix protein located?
Between capsid and envelope
What is antigenic drift?
Change in antigenicity of virus due to genetic drift
What is antigenic shift?
Recombination
Exchange of nucleotide sequences between different, but usually closely related viruses during replication
What is the most important mechanism for high genetic diversity in viruses with segmented genomes?
Reassortment (antigenic shift)
What are 4 important viral enzymes critical to viral infection?
- Lysins
- Retroviral integrase (IN)
- Reverse transcriptase (RT)
- Nucleic acid polymerases
What 3 different roles do viral nonstructural proteins do?
- Play role within infected cell during virus replication
- Act in regulation of virus replication
- Act in regulation of virus assembly
T/F: Nonstructural proteins are seen in extracellular virions
False
Incomplete virions are virions without _______ ______
Nucleic acid (empty capsid)
What is a defective virion?
Lacks full complement/copy of viral genes, resulted from mutations or errors
What is a pseudovirion?
Contains non-viral genome within viral capsid
What are pseudotypes?
When related virus infect same cell, the genome of one virus may be enclosed in heterologous capsid of second virus