13 Virus 1

Question 1

what are viruses

Answer 1

obligate intra-cellular parasites

Question 2

what surrounds a virus

Answer 2

nucleic acid surrounded by protein capsid or protein shell

Question 3

how do viruses enter cells

Answer 3

via interaction with specific cell receptors = TROPISM

Question 4

what happens when a virus enters a cell

Answer 4

following cell enter the host cell machinery is hijacked = synthesis of new virus

Question 5

how is a virus released

Answer 5

released by budding (enveloped virus) or by cell lysis or via secretory pathway

Question 6

what is an orphan virus

Answer 6

virus that doesn’t result in disease

Question 7

virion

Answer 7

virus particle

Question 8

Virus structure - nucleic acid

Answer 8

can be DNA or RNA

Question 9

nucleocapsid

Answer 9

nucleic acid plus protein

Question 10

how are capsids arranged

Answer 10

arranged in symmetrical patterns

Question 11

HIV structural arrangement

Answer 11

HIV has helical nucleocapsid and icosahedral core

Question 12

what have some viruses developed from host cell membrane

Answer 12

some viruses also possess a lipid envelope derived from host cell membrane

Question 13

what are some viruses involved in

Answer 13

involved in cell attachment and entry

Question 14

what are some of the enzymatic functions viruses have

Answer 14

> for copying viral genome (polymerases)
for trimming viral proteins (proteases)
other modifying enzymes

Question 15

how are viruses grouped

Answer 15

according to their shared properties
nature of the nucleic acid: RNA or DNA
capsid symmetry
presence or absence of an envelope
size

Question 16

how are virus families named

Answer 16

All Families have the suffix -viridae (e.g. retroviridae), whilst genera have suffix virus (e.g. flavivirus)

Question 17

hierarchy of recognized viral taxa

Answer 17

(Order) > Family > (Sub-family) > Genus > Species

Not all viruses belong to a order or sub-family

Question 18

RNA viruses

Answer 18

Take RNA put into cell and get a virus back

Use own polymerase to make a positive sense copy

Question 19

what do viruses lack

Answer 19

mitochondria and ribosomes

Question 20

what is used to replicate the viruses

Answer 20

polymerases required to replicate their nucleic acid genome (be it DNA or RNA)

Question 21

where can virus replication occur

Answer 21

only in living cells

Question 22

what mediates virus attachment to target cells

Answer 22

mediated by a specific interaction between a component (usually a protein) of the surface of the virus and a cellular receptor

Question 23

what is the capsid sometimes covered in when buds

Answer 23

sometimes the capsid is covered with the membrane of the host cell as the virus buds off

Question 24

how does a virus enter

Answer 24

Attachment and replication - Interaction with specific cell surface receptor
> Membrane fusion
- Receptor-mediated endocytosis

Question 25

what is receptor-mediated endocytosis

Answer 25

take things from outside of the cell and bring into inside

Question 26

Genome replication and virus protein production - RNA virus

Answer 26

``` virion contents: (-)RNA dsRNA (+)RNA genome replication cycle RNA to RNA ```

Question 27

Genome replication and virus protein production - reverse-transcribing viruses

Answer 27

virion contents: (+)RNA dsDNA genome replication RNA to DNA using reverse transcriptase

Question 28

Genome replication and virus protein production - DNA virus

Answer 28

virion contents: ssDNA dsDNA genome replication DNA to DNA

Question 29

Virus release

Answer 29

Nucleocapsid assembly may take place in nucleus or cytoplasm Envelope viruses bud through cell membrane (sometimes through golgi / ER) Non-enveloped viruses mature in golgi / cytoplasm - transported to surface via secretary vesicles May or may not cause cell lysis

Question 30

Bacteriophage

Answer 30

Lytic phage Temperate phage Pseudolysogeny

Question 31

Lytic phage

Answer 31

phage genome replicated, phage capsid and tail proteins are synthesized using bacterial cell machineries; the phage genome is then packaged into progeny phage particles, which are liberated via bacterial lysis

Question 32

Temperate phage

Answer 32

phage genome integrated into bacterial chromosome (becoming a prophage) persists as a latent or dormant phage Prophages replicated together with bacterial host chromosome during host cell replication and switch into lytic production upon exposure to DNA damage

Question 33

Pseudolysogeny

Answer 33

bacterial cells can’t support DNA replication or protein synthesis phage genome remains for extended period of time as a non-integrated preprophage, at which point the phage enters either a lysogenic or a lytic life cycle

Question 34

when does pseudolysogeny occur

Answer 34

nutrient-deprived conditions

Question 35

why does pseudolysigenic preprophage not replicate

Answer 35

Pseudolysogenic preprophage does not replicate and so is only inherited by one of the daughter cells following cell division

Question 36

Tobacco mosaic virus

Answer 36

ssRNA +ve

Question 37

Tobacco mosaic virus effect

Answer 37

causes mottling of leaves and fruits and affects tomatoes peppers cucumbers as well as tobacco

Question 38

what do human viruses usually cause

Answer 38

cell death and inflammation - damage to respiratory tract cells and aching body and fever as the inflammatory response of the immune system reacts to the virus proteins

Question 39

what do some latent infections cause

Answer 39

initial infection goes away but later a further sometimes slightly different infection breaks out from virus stored in the body- such as human Herpes viruses which cause chicken pox and shingles

Question 40

what is sputnik

Answer 40

Virophage virus that requires another virus to replicate inside the amoeba

Question 41

retrovirus advantages

Answer 41

effective over long periods efficient transfection ex vivo low immune response in host

Question 42

retrovirus disadvantages

Answer 42

small, max 8kb insert size inefficient transfection in vivo relies on target cell mitosis safety concerns

Question 43

retrovirus type

Answer 43

integrates with host chromatin

Question 44

lentivirus advantages

Answer 44

transfects proliferating and non-proliferating hosts and haemo stem cells new generation are self-inactivating for safety

Question 45

lentivirus disadvantages

Answer 45

need active transport into cell small, max 8kb insert size technologically challenging safety concerns, immunodeficiency origins

Question 46

adeno-associated virus advantages

Answer 46

very good length of expression especially in vivo efficient transfection in vivo low immune response in host

Question 47

adeno-associated virus disadvantages

Answer 47

safety problems owing to potential insertional mutagenesis small, max 4.5kb insert size high immuno response technologically challenging

Question 48

adeno-associated virus type

Answer 48

either

Question 49

adenovirus advantages

Answer 49

highly efficient transfection in vivo and ex vivo | transfects proliferating and non-proliferating hosts

Question 50

adenovirus disadvantages

Answer 50

repeat treatments ineffective due to strong immune response small, max 7.5kb insert size technologically challenging short expression duration

Question 51

adenovirus type

Answer 51

extra chromosomal DNA

Question 52

herpes simplex virus advantages

Answer 52

very good length of expression especially in vivo safe for use in immunocompromised patients large insert size up 30kb effective on many cell types

Question 53

herpes simplex virus disadvantages

Answer 53

difficult to produce in large quantities

Question 54

herpes simplex virus type

Answer 54

extra chromosomal DNA