Lecture 2- Viruses

Question 1

what are viruses? how do they reproduce? multicellular or acellluar?

Answer 1

acellular infectious particles that are obligate intracellular pathogens (they reproduces only inside of living cells and they lack an independent metabolism)

Question 2

what is a virus composed of? 3

Answer 2

nucleic acid genome (DNA or RNA)
capsid (protein coat)
some have an envelope

Question 3

what do viral genomes consist of? (4)

Answer 3

DNA or RNA (never both but can flip from DNA outside the living organism then to RNA inside the organism and vice versa)
single stranded or double stranded
circular or linear
segmented (can be several pieces)

Question 4

what is a virion?

Answer 4

encapsulated virus with DNA or RNA

Question 5

what is the structure of a virion? what does it consist of? 2

Answer 5

capsid (protein coat that surrounds the genome)
envelope

Question 6

what is a capsid made up of? what is their function

Answer 6

identical polypeptides (protomers)
in helical structures with nucleic acid genome is coiled inside
capsids allow for transfer of viral genome between host cells

Question 7

what are two different kinds of capsids?

Answer 7

icosahedral capsid
binal capsid

Question 8

what is a icosahedral capsid? how many sides does it have? what do the polypeptides do?

Answer 8

symmetrical geometrical shape with 20 triangular faces
protomers (polypeptides) aggregate to form capsomeres

Question 9

what are binal capsids? what is the structure? what do the parts of the structure do?

Answer 9

geometric head with an attached helical tail
genome is in head, tail is used to inject DNA into a host cell

Question 10

what is an envelope? what does it consist of?

Answer 10

a lipid bilayer surrounding the nucleocapsid that was acquired from the host membrane
consists of host lipids and spikes
ex. influenza virus has a flexible helical capsid surrounded by an envelope. has 2 major spikes hemaglutanin and neuraminidase

Question 11

what do nucleocytoplasmic large DNA viruses have that other viruses dont?

Answer 11

multi- layered structure
some of these DNA viruses can be larger than bacteria

Question 12

how does a virus infect a host?

Answer 12

attaches to specific receptors on the host cell surface
ex. HIV binds to CD4 receptor (only infects humans)

Question 13

what is an example of a virus that infects more than one species?

Answer 13

influenza
binds to a glycoprotein on animal cells
thus infecting humans, pigs, chickens, seals…

Question 14

what is a bacteriophage virus?

Answer 14

virus that infects bacteria

Question 15

what is an animal virus?

Answer 15

virus infects and multiplys only inside animal cells

Question 16

what is the goal of a virus?

Answer 16

to make more viruses

Question 17

how does the viral application cycle work? 5

Answer 17

1- absorption (attachment to the host cell
2- penetration and uncoating (entry into host cell)
3- synthesis of viral nucleic acids and protein
4- assembly of new virions
5- release of virions

Question 18

what are the two ways virions can get released?

Answer 18

naked virus: accumulate then lyse the host cell releases
enveloped virus: released by budding (virions push through the cytoplasmic membrane without killing the host cell)

Question 19

how exactly does a enveloped virus get released by budding?

Answer 19

1. envelop proteins are inserted into host cells membrane
2. viral matrix proteins bind the inner surface of the host cells membrane
3. plasma membrane buds to form the viral envelope and release mature virion

Question 20

what are the two ways for a animal virus to enter a cell?

Answer 20

fusion with plasma membrane
endocytosis

Question 21

how does an animal virus use endocytosis to enter a cell?

Answer 21

1. spikes bind to receptors
2. virus gets surrounded (enveloped)
3. capsid is removed and viral genome is released into the cell