Rapid Evolution of Viruses

Why do viruses evolve so quickly?

Because they have short generation times, high mutation rates, and strong selective pressures.

Why does fast replication speed up viral evolution?

More replication events create more opportunities for mutations.

How fast do viruses replicate compared to multicellular organisms?

Within minutes to hours, versus decades for multicellular organisms.

Why do RNA viruses mutate faster than DNA viruses?

Their replication enzymes lack proofreading.

Which enzyme do DNA viruses use?

DNA polymerase.

Does DNA polymerase have proofreading?

Yes.

Which enzymes do RNA viruses use?

RNA polymerase or reverse transcriptase.

Do RNA polymerase and reverse transcriptase have proofreading?

No.

What is the consequence of no proofreading in RNA viruses?

They accumulate frequent errors and form genetically diverse populations.

Why can high mutation rates be beneficial for viruses?

They increase adaptability.

What selective pressures do viruses face?

Immune defenses, antiviral drugs, and transmission barriers.

How can mutations help viruses evade immunity?

By altering surface proteins so antibodies no longer recognize them.

What two factors must always be mentioned together when explaining rapid viral evolution?

Variation and selection.

What type of virus is influenza?

An RNA virus with eight genome segments.

Why does influenza mutate frequently?

Its RNA polymerase lacks proofreading.

What is antigenic drift?

Gradual accumulation of mutations in H and N genes.

What is the effect of antigenic drift?

Slight changes in surface proteins reduce immune recognition.

Why must the flu vaccine be updated annually?

Because antigenic drift produces new viral variants each year.

What is antigenic shift?

Sudden reassortment of genome segments when two influenza strains co-infect a host.

Why is antigenic shift dangerous?

It creates new strains with no pre-existing human immunity, potentially causing pandemics.

What is an example of antigenic shift?

The 2009 H1N1 swine flu pandemic.

What type of virus is HIV?

An RNA retrovirus.

Which enzyme causes HIV’s high mutation rate?

Reverse transcriptase.

Why does HIV evolve rapidly within a single patient?

Reverse transcriptase introduces errors every replication cycle.

What does HIV mutation generate within a host?

A huge pool of genetically diverse variants.

How can HIV variants escape treatment?

Some mutations confer resistance to antiretroviral drugs.

What happens if a cell is infected by two HIV strains at once?

Their genomes can recombine and swap segments.

Why does recombination make HIV hard to vaccinate against?

It produces constantly changing hybrid viruses.

Why is combination therapy needed for HIV?

One mutation alone cannot confer full resistance to multiple drugs.

What is immune evasion in viruses?

Mutations change antigens so the immune system cannot recognize them.

What causes viral drug resistance?

Mutant strains survive single-drug treatments.

How does rapid mutation help cross-species transmission?

It allows viruses to adapt quickly to new hosts.

How can sudden viral changes cause pandemics?

New variants spread globally before immunity develops.