Viral biology Flashcards
what is a virus
‘DNA or RNA that is protected by a protein coat
size
25-300nm in size
consists of
RNA, DNA or both
–> double or single stranded
extracellular form
vision- protein encapsulated DNA or RNA
intracellular form
replication of DNA/RNA and proteins; assembly of virus
bacteriophages
virus which infects bacteria
mycophages
virus which infection animals, plants and fungi
virus’ are not
CELLS
virus particles
self -assemble
structure of a virus
protein coat which contains a few proteins that self assemble
proteins inside a virus known as
capsomers
protein coat known as
capsids
capsids
protect RNA/DNA of virus
virus’ can be ..
helical or icosahedral– determined by capsid
organisation of the virus particles
naked virus–> enveloped virus –>complex virus
naked virus
- capsid
- nucleic acid (DNA or RNA)
- enzymes (lysosomes, reverse transcriptase)
enveloped virus
- capsid
- nucleic acid
- enzymes
- biomembranes- lipids from the host cell
- enveloped proteins (from virus)
complex virus
- capsid
- nucleic acid
- enzymes
- complex protein tail
example of an enveloped virus
- HIV- causes acquired immunodeficiency syndrome
- influenza
example of a complex virus
T4 phage
three ways in which virus’ enter a host cell
1) endocytosis
2) membrane fusion
3) injection
endocytosis
the virus triggers clathrin-mediated endocytosis and enters the cell as a “trojan horse”
membrane fusion
enveloped virus particles bind to receptors in the plasma membrane of host and forces membrane fusion
injection
bacteriophages inject their genetic info and leave the rest of the virus particle behind
virus particles can
move within infected cells
how do virus’ move within cells
- dependent on dynein
- virus particles move along microtubules
viral particles move along
microtubules
viral replication requires
microtubules and F-actin
bi-directional motility
at around 2.5 um/s
spreading of released virus’
-smaller droplets can remain airborne for hours or even days
in public envionment
16,000 viruses/ cubic metre of air
release of an enveloped virus
1) transcription of viral RNA/DNA
2) translation
3) assembly
4) budding at C>S>M
5) release
life cycle of an enveloped virus
1) enveloped virus fuses with the membrane
2) enveloped into a clathrin pit in the cell and move towards the nucleus via molecular motors and microtubules
3) enveloped virus then releases content
4) nucleic acid goes into the nucleus and is replicated, transcribed and translated
5) new virus’ form which are then exocytosed from the cell- this process enveloped the virus
life cycle of a bacteriophae
1) virus attaches to the surface receptors
2) tails contracts, lytic enzymes break the wall and the core needle pinches the cell
3) the content of the head (proteins, DNA/RNA) is released into the cell
4) bacterial metabolism is disrupted and the genomic DNA degraded
5) Viral DNA is replicated and viral DNA is transcribed into mRNA-
6) mRNA is translated into viral proteins
- complex virus particle self-assembles inside the host
7) 50-100 phages assemble in infected cell
- lytic proteins (lysosomes) disintegrate the cell and release the phages
T4 bacteriophage
- conists of 25 structural proteins nd double stranded DNA
- injection apparatus
which proteins cause apoptosis of virus
lysosomes disintegrates the cell and releases the phages
