Lecture 3 - Viruses

Question 1

What are the key features of viruses?

Answer 1

Obligate intracellular parasites (uses/abuses host cell)
Depend on biochemical machinery of host cell to replicate; not considered a living “thing”
Can not make energy or proteins independent of host
Replication is by self-assembly of individual components, including nucleic acid and capsid
Genome is either DNA or RNA

Question 2

Describe the retrovirus life cycle

Answer 2

Example: HIV
Requires unique virion enzyme reverse transcriptase (RT).
Viral genome integrates into host cell chromosomal DNA: persistent infection
Viruses are packaged in cytoplasm and released by budding.

Question 3

Describe +ss RNA life cycle

Answer 3

Example:
hepatitis C
Entire life cycle is normally extra nuclear
Progeny viruses released by budding

Question 4

Describe - ss RNA life cycle

Answer 4

all enveloped
Examples of diseases: influenza (fusion), Ebola
Carry unique enzymes in capsids that facilitate replication
Entire life cycle is frequently extra nuclear
BUT influenza transcription takes place IN nucleus
Progeny viruses released by budding

Question 5

Why are viral infections problematic?

Answer 5

Few drugs available and Drug resistance
High mutagenic rates
Emerging infectious diseases 
Latent and persistent infections
Can initiate cancer (stage 1 slide) 
Re-emerging infectious diseases (polio)
Public health issues/ transmission: clean water, societal upheaval, education

Question 6

What is the difference between antigenic drift and antigenic shift?

Answer 6

Shift: recombination [“shuffling”], results in new subtype
Drift: random mutations, results in new strain of existing subtype

Question 7

What is the difference between a pandemic and an epidemic?

Answer 7

Pandemic: world wide spread new disease
Epidemic: disease spreads rapidly to many people