viruses

Question 1

virus =

Answer 1

fragments of nucleic acid (DNA or RNA) encoding a small number of proteins encased in a protein capsule

(some viruses → encased in a membrane)

Question 2

what 3 things are proteins in viruses used for?

Answer 2

→ replicating genome
→ packaging viral genome (capsid protein) → transporting
→ modifying host cells → enhance virus replication

Question 3

give examples of DNA viruses

Answer 3

poxvirus, herpesvirus, adenovirus, papillomavirus

Question 4

give examples of RNA viruses

Answer 4

pollovirus, HIV/AIDs virus, influenza virus, coronavirus (common cold), rabies virus, mumps virus

Question 5

single virus particle =

Answer 5

virion

Question 6

which is faster lysogenic or lytic cycles?

Answer 6

lytic

Question 7

a ____ completely depends on entering the ________ to continue their _______ cycle

Answer 7

virus, host cell, infectious

Question 8

what is budding?

Answer 8

virus takes a bit of the host cells membrane → produces progeny viruses
happens in enveloped viruses

Question 9

describe the lytic cell cycle

Answer 9

some viruses incorporate into DNA for a period of latency
→ virus enters cell and DNA/RNA is uncoated
→ DNA/RNA is replicated and translated
→ translated proteins and replicated nucleic acids → reassemble → form virion
→ virus exits cell when cell dies or by budding

Question 10

what are the 4 entry strategies for a virus to enter a host cell?

Answer 10

1) fusion with plasma membrane
2) endocytosis
3) pore formation
4) endosomal membrane formation

Question 11

which type of virus fuses with plasma membrane to enter host cell?
How does it work?

Answer 11

HIV - enveloped viruses

envelope directly fuses with membrane → releases nucleocapsid into cytoplasm → uncaring → releases contents

Question 12

which type of virus undergoes endocytosis to enter the host cell?
how does it work?

Answer 12

influenza virus

enters endosome that has become more acidic → acidification triggers fusion with endosome membrane → triggers uncoating of capsid → releases RNA genome into cytoplasm

Question 13

which type of virus uses pore formation to enter the host cell?
how does it work?

Answer 13

polio (P for pore and polio)

endocytosis of virus into vesicle → uncoating → forms a pore by a pore forming protein → makes hole in endosome → releases virus genome into cytoplasm

Question 14

which type of virus uses endosomal membrane formation to enter the host cell?
how does it work?

Answer 14

adenovirus

endocytic vesicle forms early endoscope → vesicle broken open by lysis → DNA virus enters nucleus through nuclear pore

Question 15

all entry strategies are reliant on ___________

Answer 15

host cell surface receptors

Question 16

6% of all cancer is caused by what type of virus?

Answer 16

papillomavirus (HPV)

Question 17

outer epithelial cells have a ______ replication rate

basal epithelial cells have a _______ replication rate

Answer 17

higher

lower

Question 18

in the lytic cycle, what does virus genome replication and viral proteins do?

Answer 18

increase cell cycle and prevent apoptosis

Question 19

how are benign tumours/warts formed?

Answer 19

if papillomavirus becomes incorporated into outer layer cells

Question 20

how are malignant tumours formed?

Answer 20

if there is accidental integration of virus into basal epithelial cells
→ excessive proliferation → disturbs epithelial organisation

Question 21

what does a pap smear do?

Answer 21

allows early detection of the papillomavirus

Question 22

balance between cell division and cell loss, increases tumours =

Answer 22

cell proliferation

Question 23

______ can cause cancer

Answer 23

retroviruses

Question 24

retroviruses cause cancer by incorporating human _________ into their genomes

Answer 24

proto-oncogenes

Question 25

c-raf =

v-raf =

Answer 25

cellular version of gene
viral oncogene version

raf becomes an oncogene when regulatory region is removed → human proto-oncogenes altered when incorporated into viral genome

Question 26

how do papillomavirus’ cause cancer?

Answer 26

contain oncogenes → E6 and E7 proteins,
these proteins turn up hosts replication machinery to make more virus

malfunctions when the viral genome is incorporated into host → increased production of E6 and E7 → causes unregulated cell proliferation

Question 27

why does increased production of E6 and E7 increase cell proliferation?

Answer 27

RB and E53 = host genes that REGULATE cell proliferation

E6 binds to E53
E7 binds to RB
inactivates them
causes unregulated cell proliferation

Question 28

what is C-src?

Answer 28

a kinase and powerful activator of cell proliferation

Question 29

what part of C-src is phosphorylated?

Answer 29

carboxy terminus

Question 30

phosphorylated carboxy terminus of c-scr causes the protein to do what?

Answer 30

protein folds and becomes inactivated which regulates c-scr activity

Question 31

what is missing from v-src and what effect does this have?

Answer 31

v-src = oncogenic form of c-src
→ constantly activated cell proliferator
DOES NOT HAVE CARBOXY TERMINUS

Question 32

describe the study about mice to show how oncogenes are incorporated by mistake into viral genomes and can cause cancer

Answer 32

Abelson’s leukaemia virus:
non transforming MuLV virus given to 150 mice, 1 mouse developed tumour, tumour was analysed

→ abl oncogene was present in viral genome
→ had become transforming abl-MuLV virus

the abl oncogene came from the hosts own genome