4 - Viral properties

Question 1

What is meant by obligate?

Answer 1

cannot complete its lifestyle (replicate) without being inside a host cell
(uses the host cell machinery)

Question 2

What are the characteristics of the non-enveloped virus morphology?

Answer 2

have a protein capsid and and symmetrical

Question 3

What are the characteristics of the enveloped virus morphology?

Answer 3

• have proteins around their genome
• have a lipid envelope around them which is derived from the membrane of the host cell
• are PLEOMORPHIC - have lots of different shape

Question 4

Which morphology does the Herpes virus have?

Answer 4

it is a combination of capsid and envelope

Question 5

What are the features of RNA viruses and retroviruses?

Answer 5

• use own polymerises to replicate
• very error prone and lack proofreading capacity
• high mutation rate
• RNA virus genome is limited in size die the instability of its DNA

Question 6

What are the features of DNA viruses?

Answer 6

• larger (since DNA is more stable)
• there is space for accessory genes
• genome can be one long strand or can be segmented e.g. influenza

Question 7

Viral Replication:
What is the name of the protein on the surface of the virus that binds to the receptor on the host cell in the first stage?

Answer 7

viral attachment protein

Question 8

Viral Replication:

What are the 2 ways that viruses enter the host cells?

Answer 8

• fusing with the host cell membrane and injecting the DNA/RNA genome into the cytoplasm
• enter via a series of vesicles such as endosomes

Question 9

Give the generic virus replication cycle

Answer 9

• there is an inert virus on the outside
• its viral attachment protein binds to a receptor on the host cell surface (this docks down the virus onto the cell surface)
• virus enter the cell
• the viral genome is made into messenger RNA
• host ribosomes are used to translate the mRNA and make proteins
• at the same time, the genome is being replicated (either using viral or the host cells polymerases)
• the copies of the gnome and the viral proteins assemble to form new viral particles, which than leave the cell

Question 10

Describe the replication cycle of influenza

Answer 10

• spike proteins are used to attach to the surface of the host cell
• it is engulfed and taken into an endosome
• it then fuses and releases its genome
• the genome enters the nucleus where it replicated and directs the synthesis of proteins
• they come other to form new virus particles

Question 11

Describe the replication cycle of Ebola virus

Answer 11

• starts off as a worm like virus outside of the cell
• attaches to the cell receptor and is macropinocytosis
• in the early endosome it undergoes various cleavages, so it can interact with different receptors
• the genome is released and is copied into new genomes and into mRNA, to produce proteins
• proteins and genomes come assemble and bud out to form new virus particles

Question 12

Describe the single step growth kinetics of a virus?

Answer 12

• the amount of virus at the start is know
• eclipse phase - no virus because all of it has gone into cells
• logarithmic increase - the virus makes new copies and exits the cells
• cell death - it tails off because cells start dying