27 - viral replication

Question 1

6 steps of virus multiplication

Answer 1

• attachment
• internalisation
• biosynthesis
• synthesis of virus proteins
• post translational modification
• release

Question 2

attachment

Answer 2

diffusion to the cell surface is mediated by low affinity receptor

primary receptors are protein receptors that the virus interacts with

in some viruses you need a co-factor to aid the attachment process

this ensures virus gets into the correct cell with all the machinery it needs

Question 3

attachment of a HIV virus

Answer 3

1) free HIV virus
2) Gp120 interacts with the CD4 on the cell surfaces which causes conformational change in the Gp120 protein
3) this opens up another binding site to recognise the chemokine (CCR5) receptor - the co-receptor
4) results in the fusion of the viral envelope with the cell membrane

Question 4

what receptors are used in the attachment process of viruses?

Answer 4

CCR5
ICAM-1
acetylcholine receptor
CDW150 (SLAM)

Question 5

what is the function of and what virus does the CCR5 receptor attach?

Answer 5

chemokine receptor

HIV

Question 6

what is the function of and what virus does the ICAM-1 receptor attach?

Answer 6

intracellular adhesion molecule

rhinovirus

Question 7

what is the function of and what virus does the acetylcholine receptor attach?

Answer 7

neural signal transducer

rabies virus

Question 8

what is the function of and what virus does the CDW150 receptor attach?

Answer 8

lymphocyte activation

measles virus

Question 9

internalisation

Answer 9

can either be:
• fusion from without
• receptor-mediated endocytosis

Question 10

internalisation - fusion from without

Answer 10

can only be achieved by viruses with an envelope

1) enveloped virus lands on cell surface
2) fuses to the surface
3) viral envelope binds to the membrane
4) nuclear capsid released into the cell

Question 11

internalisation - receptor mediated endocytosis

Answer 11

for enveloped and non-enveloped viruses
only way for non-enveloped viruses to enter the cell

1) virus docks on surface of cell by receptor
2) initiates plasma membrane to engulf virus and pinch off as a vesicle
3) vesicles fuse with endoscope in cell which decreases pH
4) causes a conformational change in the viral proteins so that:
• enveloped virus fuses with vesicle and genome plus associated proteins enter the cytoplasm
• genome plus associated proteins of non-enveloped virus escape from vesicle through a pore and enters cytoplasm

Question 12

biosynthesis

Answer 12

replication

transcription

translation

Question 13

synthesis of virus proteins

Answer 13

function of the proteins encoded by the viral genome:
• replication of genome
• package of genome into virus particles
• alter metabolism of infected cell

structural proteins - form part of the virus particles

non-structural proteins - enzymes involved in transcription

all viruses must compete from host cell ribosomes

protein synthesis is often inhibited in virally infected cells - or viral protein synthesis is more efficient

Question 14

post translational modification

Answer 14

viral proteins undergo same range of modifications as host cell membranes

some virus gene,es are translated to produce a single large viral poly protein that needs to be cleaved to release individual viral proteins
• proteases

Question 15

what are the 5 basic structural forms of viruses?

Answer 15

naked icosahedral: poliovirus

naked helical: TMV

enveloped icosahedral: herpes virus

enveloped helical: measles virus

complex: poxvirus

Question 16

release

Answer 16

release by cell lysis - polio

release by budding
• from PM - influenza
• from lumen of ER - rotavirus

spread from cell to cell
• via pores - herpes
• fusion of membrane - RSV

release may be preceded by a maturation step