Chapter 4 Flashcards
characteristics of viruses, who they attack
- obligated intracellular parasites, can replicate ONLY inside host cells
- no one is safe: host cells include every group of organism (bacteria, archaea, eukaryotes…)
- are called virions outside the host, exist as inert infectious particles
what is a capsid
a protein coat around a nucleic acid (where each type of protein is essentially a piece of nucleic acid enclosed within it)
how can we classified viruses (2)
by their cell host (animal, bacteria, plants..) and their type of nucleic acid (DNA or RNA)
number of proteins in simple and complex viruses
simple: 3-4 proteins
complex: more than 100 proteins
in all cases, the host cell supply what (3)
- the building block (amino acids, nucleic acids)
- the machinery (ribosomes)
- the energy requires to produce new viruses particles
what is nucleocapsid
- nucleic acid + protein coat (capsid)
what are capsomeres
protein subunit that makes up the capsid
what is the enveloppe
lipid-containing layer with embedded proteins
- the proteins of the enveloppe are virus specific and are encoded on the viral genome
- the proteins are involvend in the attachment of the virus to the next host cell
in animal viruses, the enveloppe is originated from what
the cytoplasmic membrane of the host cells
shapes of virions are determine by what and give 3 examples
by the nature of the capsomere
- helical virus, polyhedral virus, complex virus
example of helical virus
tobacco mosaic virus
how many capsomere in the helical virus (the most typical virus of many plants)
2130 capsomeres
the most common shape of the polyhedral virus
icosahedron, a regular polyhedron with 20 triangular faces and because of the geometry, only some capsomere numbers are possible
example of polyhedral virus with more faces
human papilloma virus contains 72 clusters of 5 capsomeres
viruses that are the most complixated in term of structure
the viruses of bacteria (bacteriophages)
6 parts of the complex virus
head (contain DNA)
tail (tail pins and tail fibers)
collar (between head and tail)
endplate
what does lamba, a complex virus, miss
tail fibers
why T4 virion only affect Gram-negative cells
because T4 virion recognizes specific receptors (lipo-polysaccharides) on the outer membrane and since Gram-positive doesn’t have lipo-polysaccharides, it doesn’t affect them
5 steps of the replication of a bacterial virus
- attachment (adsorption of phage virion)
- penetration of viral nucleic acid in the host cell (the protein coat remain outside)
- synthesis of viral nucleic acid and protein
- assembly and packaging of new viruses (maturation)
- cell lysis and release of new virions
* * the cell is dead
two ways the cell can go after the injection of viral DNA
lytic pathway (dangerous) lysogenic pathway (can lead to lytic pathway if the cell is stress and the prophage goes to the phenomon of induction)
3 steps of the lytic pathway (after the injection of the viral DNA)
- lytic events are initiated
- phages components are synthesized and virions are assembled
- lysis of the host cell and release of new phage virions
2 steps of lysogenic pathway
- viral DNA is integrated into the host DNA
- viral DNA is replicated with host DNA at cell division
* called prophage (it is going to replicate but it will not bother the cell, not kill it)
* ** prophage not expressed due to a phage-encoded receptor protein
3 steps of the quantification of bacterial virus by plaque assay
** the mixture containing molten top agar, bacterial cell and diluted phage suspension
- the cell-phage mixtured is poured into a solidified nutirent agar plate
- the mixture is left to solidify
- incubation allows for bacteria growth and phage replication
** the clear patch that we see is the cell lysis (bacteria that have been attack by the viruses) so the number of clear patch= the number of viruses at the beginning (approximatively)
what are viroids
they are closed circles of single-stranded RNA containing 220-380 nucleotides
replication of the viroids depend on what
it is dependent on host machinery, disease is caused by the overtaking of this machinery by the viroid
viroids are the cause of what (2)
cadang-cadang disease of coconuts (means dying)
potato spindle tuber
how viroids move from cell to cell
by using the plasmodesma
what are prions
they consist solely of protein
5 neurological degenerative disorders cause by prions
- scrapie (sheep)
- bovine spongiform encephalopathy (cattle) - BSE- mad cow disease
- creutzfeldt- Jakob disease- CJD (human)
- vCJD: transmitted by ingestion of BSE-contaminated product (human)
- kuru (human)
what do the misfolded prion proteins
they induce misfolding of the PrPc protein.
- prion protein does not replicate, it induces the accumulation of misfolded PrPc proteins, which kill the cell
- ** PrPc is primally found in neurons
exampke of helical virus in news
ebola virus
example of icosahedral virus in news
Zika Virus