Viruses and Other Acellular Agents

Question 1

an infectious virus particle is called a ____

Answer 1

virion

Question 2

what are the two components found in EVERY virion and together what are they called

Answer 2

• nucleic acid genome (RNA or DNA)
• protein capsid

together called the nucleocapsid

Question 3

what are 2 components within SOME virions

Answer 3

• lipid envelope
• replication enzymes

Question 4

the morphology of a viral capsid

Answer 4

depends on type of virus
- icosahedral (20 face triangle)
- helical (hollow tube with proteins on outside rna on inside)

or complex (neither)

Question 5

do all viral protein capsids self assemble

Answer 5

no not all but MANY

Question 6

an example of a complex viral morphology

Answer 6

bacteriophage

Question 7

if a virus has a lipid envelope is that the same as a plasma membrane ?

Answer 7

NO not the same as it contains host & viral components

Question 8

non enveloped viruses are also called ___

Answer 8

naked

Question 9

viral single stranded RNA genome maybe be __ or ___ and describe

Answer 9

+ or -

(+) = function as mRNA & are translatable
(-) = complimentary to mRNA/ not translatable until a complimentary mRNA strand is made (no stop/start codons)

Question 10

what is shown on a one step growth curve (4)

Answer 10

• latent period = no virions present in media
• rise period = # of virions in media increases exponentially
• plateau period = no more virions produced
• burst size = the # of progeny virions produced per infected cell

Question 11

5 stages of viral lifestyle

Answer 11

1. attachement to host cell
2. entry of virus / viral genome into cell
3. synthesis of essential replication components
4. assembly of nucleocapsids (maturation)
5. release of virions from cell

Question 12

how does the release step differ in naked vs enveloped DNA virus

Answer 12

naked = virions leak out / cell lyses
enveloped = virus buds from cell / exocytosis

Question 13

describe the attachment step

Answer 13

• specific interactions between viral ligands and host cell receptors

Question 14

describe the entry step (3 options)

Answer 14

endocytosis - non enveloped or enveloped
fusion- enveloped only
injection - bacteriophages only

Question 15

describe the synthesis step for DNA

Answer 15

replication of DNA AND transcription/translation to RNA and proteins is necessary for production of new virions

Question 16

what is specific about ssDNA in the synthesis step

Answer 16

dsDNA replicative form needs to be made before the rest of the processes

Question 17

describe synthesis of ss(+) RNA

Answer 17

(+) strand acts as mRNA
- only + strand ends up in capsid

Question 18

describe synthesis of ss(-) RNA

Answer 18

• capsid contains RDRP AND - strand
• neg strand needs RDRP all the time as can’t synthesis a + strand without it

Question 19

describe synthesis of dsRNA

Answer 19

• have dsRNA and RDRP in capsid (even though don’t need)

Question 20

what is special about a retrovirus

Answer 20

enveloped RNA virus that contains two copies of + RNA strand

Question 21

retroviral lifecycles steps differ from a normal virus in step 3 describe

Answer 21

3. synthesis

• reverse transcriptase (RT)
  = converts viral RNA into double stranded DNA (cDNA)
• integrase = inserts this DNA into the host genome as a provirus / when active the provirus is transcribed and replicated
• protease = processes viral proteins for assembly

Question 22

what is one of the only retroviruses to infect humans

Answer 22

HIV —— leads to aids

Question 23

does both strategies of release usually lead to the death of the host cell

Answer 23

yes

Question 24

budding occurs where there are lots of ___ proteins on the envelope

Answer 24

spike proteins

Question 25

what is a bacteriophage and the two classifications

Answer 25

a virus that infects bacteria - virulent = lytic cycle only - temperate = both lysogenic and lytic phases

Question 26

describe the lytic and lysogenic cycles

Answer 26

lytic cycle - follows 5 step cycle lysogenic cycle - allows cells to go dormant / phage dna integrates into host chromosome - when there is stress upon then it would release from the chromosome and enter the lytic cycle to try and replicate before cell dies

Question 27

when is the lysogenic cycle favoured and when is lytic cycle favoured

Answer 27

lysogenic - bacteria are nutrient starved / not dividing or growing - high MOI (multiplicity of infection) lytic - bacteria are growing/ multiplying rapidly - low MOI ( 1 virus and 100 cells)

Question 28

what is induction

Answer 28

when a prophage switches from lysogenic cycle to lytic cycle

Question 29

what is lysogenic conversion

Answer 29

a phenotypic change induced in a lysogenized host cell by a prophage

Question 30

example of a virus encoded toxin

Answer 30

cholera toxin - produced by vibrio cholerae

Question 31

compare latent, chronic infections and oncogenic and acute

Answer 31

latent infections - do not affect host but may be transmitted (lysogenic) chronic infections- result in ongoing symptoms oncogenic- viruses cause host cells to become cancerous acute - follow 5 step cycle

Question 32

describe lambdas phage genetic switch

Answer 32

lambda repressor (cl) and cro repressor (Cro) lysogenic cycle - cl is active, repressing Cro and lambda genome UV stress - destroys cl allowing Cro expression lytic cycle- Cro is active, repressing cl and activating lambda genome

Question 33

2 examples of acellular infectious agents

Answer 33

1. viroids (RNA nucleic acid based non viral) 2. prions (protein based nonviral)

Question 34

describe viroids

Answer 34

ssRNA - no capsid - causes disease in plants

Question 35

describe prions

Answer 35

- highly resistant - causes neurological diseases (Mad cow disease)

Question 36

what leads to the formation of a prion protein

Answer 36

abnormal folding of a cellular protein (PrpC)