L19 Flashcards
what is a virus
- piece of DNA/RNA, enclosed in a protective coat
- parasitic
- purpose is to deliver its genome into the host cell so it can be expressed
define capsid, nucleocapsid, envelope, and virion
capsid- protein shell surrounding genome
nucleocapsid- consists of the capsid with the enclosed nucleic acid
envelope- viral membrane, host cell derived lipid bilayer
virion- infectious virus particle
define viral proteins
- virus hijacks hosts cellular machinery to support their replication
- so viral protein mostly structural components, e.g. viral membrane + capsid
what is the function of structural proteins
- protection of the genome
- form envelope
- recognition
- packaging of nucleic acid
- ## delivery of genome
how are viruses named/classified
- by disease caused
-morphology - function
- shape of nucleocapsid
helical viruses: nucleocapsid classifications
helical viruses
- e.g. tobacco mosaic virus
- infects plants
- slinky shaped capsid, twists around to enclose genetic material
polyhedral viruses: nucleocapsid classifications
polyhedral viruses
- adenovirus
- capsids made of genetic material, surrounded by 20 triangular faces
spherical viruses: nucleocapsid classifications
- corona virus
-helical, enclosed in a envelope with spiked sugary proteins (help with sticking/entering host cells
complex viruses: nucleocapsid classifications
- bacteriophages
- lunar lander
- polyhedral head and a helical body (tail sheath) + legs (tail fibres), help transfer genetic material
stages of viral replication
- attachment + fusion: hemagglutin on influenza virus becomes attached to sialic acid sugars on target cell (commonly throat, lungs, nose)
- penetration: cell engulfs the virus by endocytosis, 2 mechanisms- fusion (virus fuse with cell membrane) or endocytosis (virus enter cell by endocytosis, or virus enclosed in vesicles in cytoplasm)
-uncoating: viral contents are released
-biosynthesis (replication): viral RNA enters the nucleus, where it is replicated by the viral RNA polymerase
- assembly: new phage particles are assembled
-release: new viral particles made + released into extracellular fluid, cell continues to make new virus, endocytosis
uncoating strategies
- pore formation
- plasma membrane fusion
-direct uncoating - partial uncoating- HIV
- endosomal fusion- influenza
endosomal lysis with nuclear membrane- adenovirus
explain RNA dependent RNA polymerase
- RNA viruses replicate in cytoplasm via RNA polymerase
- host cells lack RNA dependent RNA polymerases needed for the replication of viral RNA, so virus needs to provide the enzyme itself
- the viral RNA dependent RNA polymerase acts as a transcriptase (transcribe mRNA) as well as replicase (Replicate RNA genome)
what is viral maturation
- preparation of the virion for subsequent infection of other cells
- occur inside cell of after release
what are the 2 methods for the release of virions
lysis- naked viruses released as host cell lysed
budding- enveloped viruses by through host membrane
what is the viral cytopathic effect
- refers to the change in cell morphology caused by infecting viruses
- caused by lysis
e.g. rounding of infected cell
what is a provirus, and difference between a prophage
- inactive
- result of virus undergoing lysogenic cycle
- provirus is the genome of the virus, prophage is the genome of the phage structure
