Viruses

Question 1

describe the basic biology of viruses

Answer 1

simple acellular infectious pathogens
incapable of self replication or metabolic activity
obligate intracellular parasites

Question 2

describe the viral genome

Answer 2

can be DNA or RNA
can be linear or circular
can be single stranded or double stranded

Question 3

what does +sense and -sense mean in viral genomes?

Answer 3

in linear RNA it can be be either
+sense (mRNA) can be read for protein synthesis as it is
-sense has to be converted into +sense

Question 4

what are the components of the nucleocapsid?

Answer 4

nucleic acid + capsid (+ possible accessory enzymes)
can also be naked or enveloped

Question 5

define a virion

Answer 5

fully assembled infectious extracellular particle

Question 6

what is the capsid composed of and what is their symmetry?

Answer 6

composition - capsomeres (several grouped polypeptides)
symmetry - helical or icosahedral

Question 7

what are enveloped viruses characterised by?

Answer 7

phospholipid bilayer derived from host cells

Question 8

what can the host cell bilayer be derived from?

Answer 8

plasma membrane, golgi, ER and nuclear membrane

Question 9

what are enveloped viruses composed of?

Answer 9

lipids, virus proteins and glycoproteins

Question 10

what are host cell membranes replaced by?

Answer 10

virally encoded glycoproteins (spike proteins)

Question 11

what do viruses express to facilitate host entry?

Answer 11

glycoproteins
capsid proteins (in naked viruses)
anchored in phos. bilayer (in enveloped viruses)

Question 12

what is viral tropism?

Answer 12

ability of a given virus to productively infect a particular cell, tissue or host species

Question 13

name 6 different modes of viral transmission?

Answer 13

oral transmission, droplet transmission, direct inoculation, sexual transmission, trans-plascental, direct skin contact

Question 14

name the 7 core structures found in a typical virus

Answer 14

envelope membrane, capsid/shell, enzymes, matrix protein, transport channels, genome/nucleic acid, transmembranous glycoprotein spikes

Question 15

name some examples of respiratory illnesses caused by viruses

Answer 15

viral pneumonia, bronchiotitis, common cold

Question 16

what is a zoonoses?

Answer 16

an infection passed from a non-human host to a human host

Question 17

what are some key features of human herpesviruses?

Answer 17

persist for the lifetime of the host
remain latent (non replicating)

Question 18

what kind of virus is HIV?

Answer 18

single stranded +sense RNA retrovirus

Question 19

what is macropinocytosis?

Answer 19

where the virus attaches to the host cell and is engulfed by the host cell membrane

Question 20

what is membrane fusion?

Answer 20

where the virus inserts itself into the host cell

Question 21

what can occur after a viral infection?

Answer 21

virus can be released out of host
virus can be maintained in host cell cytoplasm
virus can be incorporated into genome
virus can become oncogenic

Question 22

why do viruses show genome variation?

Answer 22

evolutionary pressure from host immune system or antiviral drugs

Question 23

what 3 mechanisms can cause viral genome variation?

Answer 23

mutation, recombination, gene switching/reassortment

Question 24

what characteristics of a virus can influence the rate of mutation?

Answer 24

RNA viruses mutate faster than DNA viruses
single stranded mutates faster than double stranded
smaller viral genomes mutate faster than larger

Question 25

what 3 mutation types are common in viral mutations?

Answer 25

insertion, deletion and substitution

Question 26

what enzyme is required to replicate RNA viral genomes?

Answer 26

RNA dependant RNA polymerase

Question 27

under what conditions can recombination/reassortment occur in viruses?

Answer 27

if 2 strains of a virus infect the same host

Question 28

define viral genome recombination

Answer 28

the exchange of entire genes between the 2 strains

Question 29

define viral gene reassortment

Answer 29

the exchange of entire segments of genome between strains

Question 30

what is the difference between antigenic drift and antigenic shift?

Answer 30

antigenic drift - gradual change in genetic makeup
antigenic shift - sudden change in genetic makeup