Viral Pathogens Flashcards
what is phage lambda
- enteric bacteriophage
- infects only E.coli
- study of phage yeilded fundamental discoveries in gene regulation - most notably the control of lysogeny
*injects DAN that is replicated in the bacteria
how does phage lambda inject
- phage tail fibers bind to a specific outer membrane protein involved in uptake of maltose 9maltose proin) and injects its DNA into the cytoplasm
structural characteristics of phage lambda
- lambda particle (wiron) is typical of tailed phages
- has capsid head with icosahedral preotin complex
- contrains linear dsDNA genome
- tail consists of sheath plus internal tube and tail fibers (helps in attachment to host cells)
*exact length of tail depends on “tape measure protein” (protein H)
*how it works is still unclear
describe the lytic cycle of bacteriophage lambda
- phage hijacks host resources and proein synthesis machinery
- phage DNA replicated in the host cytoplasm to generate many progeny genomes
- structural proteins are assembled to form empty caspids, tails and tail fibres
- Porgeny genomes are packaged into capsid heads until the heads are ‘full’
- filled capsid heads are attached to tails
- late phage proteins: holins and edolysins are synthesized - lyse host cell to release the progeny
what is the prophage state
-phage genome integrates in and replicates within bacterial host genome
what are lysogens
- bacteria carrying the phage genomes and producing phage encoded proteins
describe lysogeny and temperate phages
- phage infects a cell
- phage DNA becomes incorperated into the host genome
- cell divides and prophage DNA is passed on to daughter cells
- Under stressful conditions the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle
- Phage DNA replicates and phage proteins are made
- New phage particles are assembled
- the cell lyses, releasing the newly made phages
how can engineered viruses be used to fight bacteria
- virus targets bacteria making it more susceptible to antibiotics
what type of virus is influenza
negative (-) strand RNA virus
*bacteriophage was a ds DNA virus
3 types of influenza
Influenza A: one of the msot common life threatening viruses
- approx 10% of pop are infected every year
Influenza B: narrower host range than influenza A - can cause serious disease but mutates much more slowly
INfluenza C: narrower host range than influenza A, cau cause serious disease but nto spread as easily
WHat is H7N9
- influenza virus
- proposes a very serious desiease in high proportion of infected poeple
- not transmisible from person to perfom only bird to person
- big fear si the virus will mutate and be able to be transmitted from person to person
- future strain with seriousness of H7N9 and transmissibilty of H1N1 would be really bad
diff between flu and a cold
- cold noramly caused by rona virus and flu by influenza
*diff viruses cause diff symptoms
describe the structure of the influenza Viron
- flu virus has no geometic caspid
- shell of matrix proteins (M1) that surround the 8 linear (-) RNA chromosome segments each coated with nucleocaspid
- matrix shell is surrounded by a membrane envelope - derived from the host cells durign budding
- two major viral envelope proteins Hemagglutinin (HA) and neuraminidase (NA) stud the surface of the vrius
describe the influenza virion genome
- 8 negative sense RNA segments (wavy purple thigns in picture)
- each coated with nucleocaspid proteins (NPs) *coating is the pink
- each encodes 1 protein
- 2 segments undergo splicing to encode 2 further proteins
- Each segment is packaged with an RNA dependent RNA polymerase (yellow dot on picture)
- During viral assembly of an infected hsot cell the segmetns are packaged randomly
- only 1 in 400 packaged virruses will be capable of subsequent infection (dont want to kill host too quick and illicit toos trong of an immune response right off the bat)
what are the advantages of a segmented genome
- continuously changes antigenic determinants (why need diff flu shots each year) - by doing so it evades host adaptive immunity
- two or more strains can infect the same host cells
*if had two strains infeting at same time would have 16 individual segments that could package together so would need lots of antigens to fight against
- reassortment is why we cant regognize it from year to year
- segmented genomes allow for reassortment (between the different virus strains) of genetic info generating drastically new strains more quickly then viruses with non egmented genomes
- influenza also continuously acquires small mutation that can lead to new phenotypes with respect to drug resistance & host range
describe the steps of replication of the influena virus
*viral components must travel in and out of nucleus
*envolope proteins must be made and trafficked through the ER golgi
- Viral (-) RNA segments (NP coated) are uncoated and enter the nucleus
- attacked viral RNA polymerase synthesizes (+) strang RNA. the + RNA strand is used as mRNA or as templates for generating progeny -RNA
- mRNA travels to cytoplasm for translation to viral proteins; viral coat proteins are embedded in host cell membrane
- Genome packaging proteins, viral RNA polymerase, RNA segments coated with newly made nucelocaspids- exported to cytoplasm and translocate to host cell membrane
- enveloped virus is released by buding and cleavage
what enzymes are required for the relase of the virus
Viral encoded neuraminidase and host protease enzyme
why do we need flu shots every year?
- drifting: ability of influenza virus (A and B) to mutate and change slightly
*usually becuase of RNA replication errors in HA and NA genes
- Shifting: a big change in the structure of the flu virus, can be caused by creation of new virus species
*reassortment of genes from 2 diff viruses mixing in single host (usually pig(
