Topic 5 - Viruses Flashcards
when did virology begin as a science?
late 1800s
what did Dimitri Ivanovski discover?
infectious tobacco mosaic virus isolated in filtered, bacteria-free fluid;
means causative agent was smaller than bacteria (virus)!!!
What did Walter Reed discover?
yellow fever is a virus transmitted by mosquitoes (jaundice, yellow-looking eyes)
Felix D’Herelle discovered?
bacteriophages (coined term “plaque”)
virus (size, genome size, how they survive)
- intracellular obligate parasites
- typically btw 10-100nm
- genome typically a few thousand to 200,000 nucleotides long (very few genes!)
what are exceptions to the small size of viruses?
all amoeba viruses!
viral genome types & physical structure
- single/double-stranded, DNA/RNA, linear/circular
- protein shell (capsid) around genome
– composed of many capsomere proteins
– capsid and genome together = nucleocapsid - possible envelope (cell-derived membrane around capsid)
virus - what is a capsid?
protein shell (around genome)
virus - what is a nucleocapsid?
capsid and genome together
capsids shape
- often exhibit either helical or icosahedral (20 sides of triangles, 3 capsid proteins per triangle on corners)
- can take on irregular or complex shapes
bacteriophage structure (4)
top to bottom:
genome (inside capsid)
capsid (shell)
tail (pillar looking “body”)
tail fibers (like little legs)
what is common for bacteriophages?
to inject genomic information into host
viral envelopes
enveloped virus
- a plasma membrane surrounds the nucleocapsid
naked virus (nonenveloped virus)
- no plasma membrane
viral replication steps (6)
- adhere (receptor in host membrane recognized by viruses)
- stick to a host cell - enter
- uncoat
- release genome - synthesis
- express and replicate genome - assembly
- create new virus particles (viral DNA + viral proteins) - exit
- new particles leave host cell
what is arguably the most important part in viral replication cycle?
entering the host cell
what receptors do HIV attach to on host cells?
CD4 receptors
T/F: Animal viruses need to contend with a cell wall during entry; elaborate (2)
FALSE!
entering animal cells:
- endocytosis
- membrane fusion
which one is outside of the other structure part? viral envelope and nucleocapsid
the envelope is outside the nucleocapsid