Sections 1-2 Final Exam Flashcards
viruses can be grouped by:
host range, structure, genome, transmission mode
The Baltimore scheme for classification of viruses has ____ categories
Seven (7)
The Baltimore scheme categories:
- +ve ssRNA
- -ve ssRNA (goes to +ve by RdRp)
- dsRNA (goes to +ve by RdRp)
- dsDNA (goes to +ve by DdRp)
- ssDNA (goes to +ve by DP then DdRp)
- +ve ssRNA (goes through RT to make sDNA then Dp to dsDNA then DdRp)
- ss/dsDNA circle?
one of the most important and useful findings of bacteriophage research:
restriction enzymes
How were restriction enzymes discovered?
Werner Arber- Noble Prize:
a host’s range changed depending on the host strain the viral particle came from
- observed that viruses can replicate In any permissive cell but can only replicate in restrictive cells if they came from that cell lineage
- observed that upon a viruses entry into a restrictive cell, its viral DNA was fragmented (its the target)
- Restorative cells can allow a virus to be able to infect a restricted cell
2 key components to the finding of restrictive enzymes (by Werner Arber)
“r” restriction: cell has resistance to foreign DNA and produces enzyme that cuts it up
“m” modification= ability for a virus to confer resistance against “r” ad modify its DNA to protect it from the cutting enzyme
The bacteriophage piX174 controls its transcript levels through _____
- differences in promotor strengths pB>pD>pA
- Terminators stop RNA pol so transcription doesn’t always go to the end
The bacteriophage piX174 controls its protein levels through _____
- controlling transcript levels (amount of mRNA) through promoters and terminators
- Nested genes: have weak ribosomal binding sites so they are translated less often (non structural or replication)
ex. non essential, lysis, scaffolding
phage lambda discovery
Discovered by Esther Lederberg in 1951 from an E.coli strain (k-12)
in E.coli strain (K-12), phage lambda is a
lysogen (able to generate lysis) and exist as a prophage (Ur-lambda primitive)
phage lambda due to its two decision cycle it was one of the most well-studied, and they found that the structure of lambda virions ___
has an obvious pattern of gene organization verses where the proteins end up in the particles (head to tail)
a recombinant lambda version was obtained from Paris and Pasadena (Papa) and it______
did NOT have tail fibers, moves easier in soft agar, and makes larger plaques
phage lambda Papa has a ______-_____ ______ preventing its tail gene from making tail fibre proteins
therefore, not the mother of all lambda phages
frame-shift mutation
it was found that Ur-λ adsorbs to the cell better than papa-λ, due to_____
a LamB maltose transporter receptor, only recognized by the J protein on the TAIL
Which one can grow in glucose
Ur-λ (has the tail so can grow even with very little receptors
tails not essential but makes them efficient and better at binding to cells
Phage λ strains WITHOUT tails, are incapable of attaching to cells when there is ____
low amounts of receptor present
All siphoviruses have long non-contractile flexible tails of different sizes, why?
but all λs (a specific phage) have the same size
Hendrix showed that the lambda protein H is a molecular ruler to control tail length
If you delete parts of H, you get shorter tails
H size directly proportional to tail size
Similar to H, different siphoviruses have different ___ _____Proteins showing a very strong relationship between gene size and tail sizeTape Measure Proteins
Tape Measure Proteins
Phage λ DNA has 12 nt ssDNA ends called ____ _____ on the ends
Genome circularizes after entering the cell through the complimentary cos sequences
cos sites (cohesion)
Phage λ: after infection and circularization of the DNA, 2 genes are expressed: ____ and _____
those help make more genes such as ___
N and cro
cll
Phage λ: If lysis:
replication, structural and lysis genes turned on
Phage λ: If lysogeny: only 2 genes subsequently expressed – cI and int
– cI and int
DNA integrates (by protein encoded by int), then only cI is expressed during lysogeny
Phage λ: if lysis, activates expression of ____ and __ genes
structure & lysis
Phage λ: if lysogeny: expresses genes ___ and ___
cI and int
Immediately after infection, only the cro and N genes get transcribed because only the ___ and ____ are bound by the host’s RNA pol
PL and PR
transcription stops after cro and N because of the terminators
TL1 and TR1
After N and Cro get translated, they bind to DNA and RNA pol at ___ sites
nut
nut sites are named for N utilization as N is a ____ _______ protein
anti-terminator
N is an anti-terminator so it leads to continuous RNA pol transcription past terminator to make __ gene
cll
If cll is acted upon by proteases and inactivated, it means the cell is well growing and active and the _____ cycle occurs
lytic
If cll is not inactivated, It means the cell is in poor state, and the _____ cycle occurs
lysogenic
When cll gets degraded, activates replication and lysis genes and inhibits cl
