Exam 2

Small sub cellular particles that can replicate only within living host cells. Obligate intracellular parasite

RNA or DNA genome enclosed in a protein shell (capsid) which together are called the nucleocapsid. Some contain viral envelop, a membrane that surrounds the capsid

Dimitri ivanovski in tobacco plants

Walter reed. Transmitted by mosquitos

10-100 nanometers

Few thousand to 200,000

Mimivirus- 400 nm Megavirus chilensis- genome of 1.2 Mbp Pandoravirus salinus- 2.47 Mbp Pithovirus sibericum- 1.5 micrometers long and 500 nm wide

Subunits of the capsid that are made of 1 or more polypeptides

Helical morphology- capsomeres form a helix and the capsid resembles a hollow tube Icosahedral morphology- capsomeres form a 20 sided polygon and each capsomeres makes up a face of the icosahedron

Only bacteria, no plants or animals

Animals, very few for plants or bacteria

Felix d’Herelle

Humans Non-enveloped, icosahedral 30nm 7,700bp ssRNA

Tobacco and related plants Non-enveloped, helical 300x18 nm 6,400 bp ssRNA

E. coli Non-enveloped 200x90 nm 170,000bp dsDNA

Humans Enveloped, complex 300x250 nm 186,000bp dsDNA

Amoeba Enveloped, complex 400nm 1,200,000bp dsDNA

Plasma membrane

Through the viral attachment protein on the surface of a virus and the receptor with which the attachment protein interacts. (spike like structure)

• virus attaches to cell receptor –> endocytosis is initiated –> endosome forms with the virus inside –> nucleocapsid escapes to the cytoplasm and uncoats to release the genome • virus attaches to the cell receptor –> conformational change in the attachment protein and bound receptor initiates membrane fusion –> viral envelop fuses with plasma membrane –> nucleocapsid enters the cytoplasm and uncoats to release the genome • virus attaches to the cell receptor–> endocytosis is initiated –> endosome forms with virus inside –> low pH of endosome initiates fusion of the viral envelop with the endosome membrane and the nucleocapsids are released

• attaches to the cell • entry and uncoating of the viral genome • gene expression and protein production • genome replication • assembly and exit from the host cell

• coevolution hypothesis- viruses may have originated prior to or at the same time as the primordial cell and have continued to coevolve with these hosts • regressive hypothesis- viruses may represent a form of “life” that has lost some of its essential features and has become dependant on a host • progressive hypothesis- viruses may have originated when genetic material in a cell gained functions that allowed the DNA or RNA to replicate and be transmitted in a semi-autonomous fashion

• lytic cycle- virus enters, replicates, and lyse host cell • lysogenic cycle (temperature phage)- phage integrates their genome into host genome (prophage), prophage genome is replicated until stress occurs and then enters the lytic phase

Inoculate appropriate cells with virus, as the viruses are replicated the bacterial cells die (due to lysing), and the culture starts to turn from turbid to clear as the cells die. Afterwards the culture can be filtered to get rid of cell remains