Virology Flashcards
What is a virus?
- An infectious agent
- Can only replicate in a host
- Non living form of life
- They are extremely small
- Tailored for a particular host
What are the 5 morphological groups of viruses
- Naked polyhedral virus ex. Mastadenovirus
- Naked helical virus
- Enveloped polyhedral virus ex. herpesvirus
- Enveloped helical virus ex. influenzavirus
- Complex coated virus ex. Mu bacteriophage
What are the 4 systems of taxonomy?
- Holmes classification (1948)
- LHT system (1968)
- ICTV (1990)
- Baltimore classification (1970)
What is the nature of the viral genome?
They are obligate intracellular parasites
Why study viruses?
Has lead to many discoveries such as - DNA carries inherited information -enzymes involved in cellular DNA replication - RNA splicing Isolation of oncogenes
What are oncogenes?
a viral or cellular gene whose expression can leasd to cell transformation or tumorigenesis
What is the range of the smallest viruses and give an example
10-20 nm
ex Picornavirus
What is the range of the largest viruses and give an example
<1 micrometer
ex. Poxviridae (can be seen by phase contrast microscopy)
Why can viruses only replicate within a host?
- lack ability to synthesize basic building block
- can’t generate energy
- don’t have enzymes for protein synthesis
What is the difference between a capsid and a nucleocapsid?
The nucleocapsid is a capsid with enclosed genome
What are the 7 viral groups within the Baltimore classification?
I. dsDNA - Poxviruses
II. ssDNA - Parvoviruses
III. dsRNA - Reoviruses
IV. +ssRNA - Togaviruses
V. -ssRNA - Orthomyxoviruses
VI. ssRNA-Reverse transcriptase with DNA intermediate - Retrovirus
VII. dsDNA-Reverse transcriptase - Hepadnaviruses
What are the components of the capsid?
Capsid -> capsomoere -> protomer
What happens to a helical capsid within an envelope?
The capsid is less rigid than if it were naked and may contain gaps exposing the nucleic acids
How are helical capsids formed?
When the nucleic acids bind to protomers within a disk creating a locked washer then more disks can stack,
What describes helical capsids?
- number of sub units per turn
- displacement along the helical axis between one sub unit and the next
What is the problem with polyhedral capsids and how do they over come this?
problem: protomers are asymmetric, so multiple protein-protein interactions of both sides
solution: arrange protomers in triangular configurations
What is quasi-equivalence?
One subunit has different interactions with other subunits to allow for a more complex capsid
What does the triangulation number (T) tell us?
That there are T multiples of 60
Describe the genome and capsid of Parvoviridae.
- ssDNA
- T=1
Describe the genome and capsid of caliciviridae.
- ssDNA
- T=3
Describe the genome and capsid of Caulimovirus
-dsDNA
T=7
Describe the genome and capsid of Hepadnavirus
-dsDNA
T=4
What are envelopes composed of?
- lipid bilayer from host
- viral glycoproteins
What are matrix proteins?
They are proteins that interact with the capsid and the envelope
What can the viral envelope be derived from?
- plasma membrane
- Golgi apparatus
- nuclear membrane
Why don’t plant viruses usually have envelope?
The envelope would cause difficulties in viral penetration and viral release
What does MOI stand for?
Multiplicity of infection
What does MOI mean?
the number of infectious virus particles per cell
In general what are the 7 steps of virus replication?
- Binding to cell receptor
- Entry into cell and uncoating
- Early gene expression ->those for replication of genome
- Replication of viral genome
- Late gene expression ->those of making structural proteins
- Assembly of virions
- Exit