Virology 2 Flashcards
How do virus’ attach to host cells?
Random collisions
Attachment not random - specific receptors
Nature of cellular receptors varies
Receptor specificity accounts for the fact eukaryotic viruses infect specific organisms and particular tissues within the host
Describe the adsorption of T even bacteriophages
Attachment of tail fibres
Base plate settles on surface
Conformational changes occur in base plate/sheath
Tail sheath shortens
Central tube pushed through bacterial wall
DNA is extruded into host cell
What are the two major pathways in bacteriophage life cycle?
Lysis - acts as virulent phage
Lysogeny - acts as temperate phage, remaining within host cell without destruction
What is a prophage and what is a lysogen?
Prophage - form of the virus
Lysogen - infected bacterium which can still reproduce
Describe the Lytic cycle of a virus
Attachment - binding sites must match receptor sites on host cell
Penetration - viral DNA is injected into bacterial cell
Biosynthesis - genome replication, transcription, translation using host cells machinery and enzymes
Assembly (maturation) - viral particles are assembled
Release - lysis
What is viral replication in terms of growth?
A one step growth curve
What is lysogenic conversion?
The altering of surface components of the host making it immune to other bacteriophages
What is transduction?
Horizontal gene transfer that occurs in salmonella, E.coli and staphylococcus aureus
Donor bacterium to recipient bacterium
Mediated by bacteriophages and viruses
Generalised and specialised transduction
What is generalised transduction?
Random DNA segment transferred
Phage has wrong DNA so defective but recipient bacterium may gain genes
What is specialised transduction?
Certain host sequences transferred + phage
How do animal viruses replicate?
Adsorption Penetration and uncoating Replication of viral nucleic acids Synthesis and assembly of viral capsids Release of mature viruses
Method used varies with type
How are viruses released from a cell?
Either naked or enveloped
Virus encoded proteins incorporated into the plasma membrane
Nucleocapsid simultaneously released and the envelope is formed by membrane budding
Special M protein attaches to the plasma membrane - aids in budding
Process can involve nuclear envelope, E.R and Golgi apparatus
What is antigenic drift and antigenic shift?
Drift - a small change due to mutation in antigenic character of an organism, change unrecognised by host immune system
Shift - most serious - major Change in the antigenic character that makes it unrecognised by the hosts immune system -> pandemics
What are the 5 steps of viral replication?
Adsorption (attachment) Penetration Biosynthesis Assembly Release
