M: Virology 1 - Week 11 Flashcards
What is a virus? (2)
An infectious, obligate intercellular molecular parasite containing a DNA or RNA genome that is packaged into a virion particle from host to host
What do viruses require for replication?
Totally dependent on a living host cell for propagation and replication
What type of genome do viruses have? (2)
DNA or RNA genome
Is the viral genome single or double stranded?
Can be either
How big are viruses compared to bacteria? What about compared to eukaryotic cells?
Small compared to bacteria
Very small compared to eukaryotic cells
How does virus receptor-binding compare between viruses?
Specific: each virus has a receptor-binding/virus-attachment protein for initial contact with host cell receptors and entry into target cell
How are new virus particles assembled?
Are assembled from new viral components synthesised in infected cells
What is the information contained in viral genomes used for?
Viral genomes contain all the information to initiate and complete an infectious cycle
What are the 2 phases of a virus?
Virion
Infected cell
Define Virion
The complete, infective form of a virus outside a host cell, with a core of RNA or DNA that is either single or double stranded, and a capsid
(Also: an archer from fire emblem awakening. A very posh and flamboyant man)
What is a capsid?
A protective protein coat for the genome
Are viruses cells? Explain
No!
Viruses contain NO ribosome machinery for protein synthesis
What is the size range for viruses? What is noteworthy about this?
Range from 20nm to 250-300nm
These sizes are too small to see on a light microscope. Need an electron microscope to view
What is necessary for sucessful electron microscopy of viruses? (2)
Require pure particles with proven infectivity
Negative staining also necessary
What can you use for negative staining of viruses in electron microscopy?
Potassium phosphotungstate
What does X-ray crystallography of viruses require?
Computer for image reconstruction of virus
What does the virion sometimes posses?
An envelope made of cell membrane modified to contain virus proteins
What are capsomers?
Clusters of capsid protein subunits
What is an envelope?
A lipoprotein membrane surrounding either nucleocapsid or capsid
What is a nucleocapsid?
The proteins most closely assembled onto the viral nucleic acid (sometimes this IS the capsid protein)
Where are the phospholipids of the envelope derived from?
From the host cell membrane
What codes the glycoproteins of the virus envelope?
Virus-encoded
What is a virus matrix?
A layer of protein that connects the capsid to envelope glycoproteins
Name the 2 different forms of capsid symmetry
Icosahedral capsid
Helical capsid
What are the 3 different axes for the icosahedral symmetry
Twofold axis
Threefold axis
Fivefold axis
Provide 3 examples of viruses with icosahedral symmetry
Adenovirus
Herpesvirus
Papillomavirus
What 2 conditions do adenoviruses cause?
Respiratory illness
Conjunctiva
How many species of herpesvirus are there? Name 4
8 HSV Cytomegalovirus Varicella zoster EBV
What does papillomavirus cause?
causes warts. These warts can become malignant (on genitals)
Describe the architecture of helical capsid symmetry. What does it look like?
A planar net of identical protein subunits wraps around the nucleic acid to form a protective layer
Provide 2 examples of viruses with nucelocapsids of helical symmetry
Mumps virus
Influenza virus
What symmetry do poxyviruses have?
They are an exception to the rule and have neither icosahedral nor helical symmetry. Their symmetry is COMPLEX
Which virus is the largest?
Poxyviruses are the largest
How many different proteins are present in the poxyvirus virion?
Over 100
What symptom does rotavirus infection typically cause?
Diarrhea (in children)
Is Rotavirus considered hardy or sensitive? Why?
Hardy. It survives passage through the gut and even sewage treatment.
- this is because it has 2 protein layers (outer and inner capsid) that protect the inner nucleic acid
What is meant by the term “Naked Virus”?
A virus that has no envelope
Does rotavirus have an envelope?
No. It is a naked virus