Introduction to viruses Flashcards
What is a virion?
Complete virus particle as it exists outside the cell (e.g. with any protein coat and envelope it may possess)
What are the main structural components of a virion?
Nucleocapsid
Envelope (not always present)
What is a nucleocapsid?
The genome and capsid
Genome = genetic material
- may be ss or ds, RNA or DNA, and linear or circular
Capsid = protein coat for genome
- made up of capsomeres (individual protein molecules)
- may be helical, icosahedral or complex in geometry
What is an envelope?
A lipid bilayer - formed from membrane of host cell
Protein and glycoprotein spikes - stick out through envelope
What may the protein and glycoprotein spikes assist?
May aid attachment/uptake/uncoating of the virus
What form can RNA be translated into a protein?
+ve stranded RNA can be translated directly into a protein by a ribosome
-ve stranded RNA must be transcribed to +ve stranded RNA first
What type of viruses are there?
DNA viruses
- ss evnveloped
- ds enverloped
- ds naked
RNA viruses:
- ss -ve enveloped
- ss +ve enveloped
- ss +ve naked
- ds naked
Give example of a family of virus with ss enveloped DNA.
Parvoviridae family
e.g. Parvoviridae B19
- causes slapped cheek syndrome (erythema infectiosum)
> rash in kids, may produce temporary arthritis
> dangerous in pregnancy/sick cell
What type of virus is the Orthomyxoviridae family and give example(s)?
Single stranded -ve enveloped RNA
- Influenza virus
What type of virus is the Paramyxoviridae family and give example(s)?
Single stranded -ve enveloped RNA
- Respiratory synctial virus
- Parainfluenza virus
- Measles
- Mumps
What type of virus is the Rhabdoviridae family and give example(s)?
Single stranded -ve enveloped RNA
- Rabies virus
What type of virus is the Hepadnaviridae family and give example(s)?
Double stranded enveloped DNA
- Hep B
What type of virus is the Herpesviridae family and give example(s)?
Double stranded enveloped DNA
- herpes simplex
- varicella zoster
- CMV
- EBV
What type of virus is the Poxviridae family and give example(s)?
Double stranded DNA enveloped
- Molluscum contagiosum
- Variola/Vacinnia (smallpox/cowpox)
Double stranded DNA naked
- Adenovirus
- Papillomavirus
What type of virus is the Calciviridae family and give example(s)?
Single stranded +ve naked RNA
- Norovirus
What type of virus is the Picornviridae family and give example(s)?
Single stranded +ve naked RNA
- Poliovirus
- Rhinovirus
- Coxsachie virus (hand foot and mouth, gastroenteritis)
What type of virus is the Astroviridae family and give example(s)?
Single stranded +ve naked RNA
- astrovirus (causes gastroenteritis)
What type of virus is the Flaviridae family and give example(s)?
Single stranded +ve enveloped RNA
- yellow fever
What type of virus is the Retroviridae family and give example(s)?
Single stranded +ve enveloped RNA
- HIV
What type of virus is the Togaviridae family and give example(s)?
Single stranded +ve enveloped RNA
- Rubella virus
What type of virus is the Reoviridae family and give example(s)?
Double stranded naked RNA
- rotavirus (gastroenteritis in kids)
What are the six key stages to the viral replication cycle?
Attachment Penetration Uncoating Genome replication and protein production Assembly Release
How can viruses attach to cells?
2 possible ways:
1) Attachment structures on virion surface (e.g. glycoproteins in spikes)
2) Host receptor molecules (i.e. mimic hormones and fit into host cell receptors)
What are the three mechanisms of penetration?
Receptor mediated endocytosis
Membrane fusion
Viral Translocation
What occurs during the uncoating stage?
Dissasembly of virus to point where genetic material can be accessed
- involves envelope uncoating and capsid disassembly
What are the function of RNA polymerases?
Transcribe DNA into mRNA
What are the function of DNA polymerases?
Replicate, i.e. make dsDNA from dsDNA
Name four aspects concerned with DNA in capsid replication or protein production.
Early protein production (may be enxymes, proteins to divert host machinery)
Viral DNA production (enabled by early proteins)
Late protein production (necessary for capsid assembly)
Nucleocapsid assembly (from vDNA and capsomeres)
How do vRNA make copies of themselves?
They may:
- carry ready made RNA polymerase to copy vRNA
- carry ready made RNA transcriptase to make DNA from vRNA
- contain a gene to produce a vRNA polymerase (only occur in +ve ss or ds RNA viruses)
What problem does vRNA have in making copies of themselves?
Unable to make copies of themselves by using host machinery due to mRNA not being copied
What is the vRNA to protein ratio for translocation?
One molecule of vRNA may only translate into one protein
What occurs during the assembly stage of viral replication?
Nucleocapsid assembled in cytoplasm
What occurs during the release stage of viral replication?
Naked viruses:
- can only be released by cell lysis
Enveloped viruses:
- enveloped proteins embed themselves in cell membrane and nucleocapsid associates with membrane
- membrane evaginates forming a vesicle around nucleocapsid which becomes envelope
