8/ viral genetics Flashcards
(16 cards)
what are viruses
- genetic elements that can’t replicate independent of a living host cell
- they can exist as virus particles outside of the host
how small are smallpox and poliovirus
- 200 nm and 28 nm
range in size of viral genomes
- 0.5-1000 kb
- some viruses have less than 5 genes
what is the virion
- extracellular form - nucleic acid surrounded by proteins
what is the intracellular form
- the replicative state
- ie not virion
what does circle w vertical line through stand for
phage
how does CD508 latch onto c difficile
- c difficile has outer protein layer which CD508 recognises and binds to - comp
- then structural change - tail contracts to allow dna to be injected into cytoplasm, emptying head
viral genomes: size, rely on, genetic material, — stranded, linear/circular?
- v small
- host replicative and metabolic machinery
- dna/rna
- single/double stranded
- linear/circular - can transform once in host
TMV - example of capsid taking up little genome space
- only one protein copied many times
- wraps into helix around rna
- self assembly so only needs 1 protein gene to make it up
what is an icosahedron
- highest level of symmetry any shell can make, spherical
- only 2 dif types of protein
- assembles almost on its own with some help from scaffolding proteins
how are tails composed
- 2 proteins - 1 for outer sheath, 1 for inner tube
5 stages pf virus life cycle
attachment, penetration, synthesis of nucleic acid and protein, assembly and packaging, release - lysis
early and late proteins, why is timing important
- early: replication of viral nucleic acid and enzymes, sigma factors
- late: includes coat proteins
- make sure genetic material fits in virus, doesn’t waste coding on unfilled coats
mechanisms used by t4 phage to ensure its genes are transcribed
- tricks host cell into responding using viral sigma factors
- so t4 doesn’t need to code its own rna polymerase
- rna polymerase modified to recognise promotors on the phage dna
- phage encodes anti sigma factor which binds and deactivates host sigma factor 70
- for early proteins host sigma factors are used
t4 - how is the switch from early protein to middle protein transcription achieved?
- some phage proteins modify host rna polymerase alpha subunits
- other early proteins bind to host rna polymerase
- these modifications alter the polymerase specificity as to recognise middle promotors
- MotA (early protein) recognises a sequence in the middle promotors and guides rna pol to correct site
- proteins: bind, modify, guide
what does transcription from late promotors in t4 require
- requires new t4 encoded sigma factor
