Unit 2

Question 1

What is the basic structure of all viruses?

Answer 1

A nucleic acid core surrounded by a protein capsid.

Question 2

Do viruses have cytoplasm?

Answer 2

No, they are not cells and lack cytoplasm.

Question 3

What types of nucleic acids can viruses contain?

Answer 3

DNA or RNA; circular or linear; single- or double-stranded.

Question 4

What is a capsid?

Answer 4

A protein shell that surrounds the viral genome.

Question 5

What is a viral envelope and where does it come from?

Answer 5

A membrane-like structure derived from the host cell’s membrane, containing viral proteins.

Question 6

What are the two main viral capsid shapes?

Answer 6

Helical (rodlike) and icosahedral (spherical with 20 facets).

Question 7

What is binal symmetry?

Answer 7

A combination of helical and icosahedral symmetry, seen in bacteriophages like T4.

Question 8

Which virus shape often includes an envelope?

Answer 8

Many animal viruses, such as influenza, have envelopes.

Question 9

What are viruses obligate to?

Answer 9

They are obligate intracellular parasites.

Question 10

What is host range?

Answer 10

The types of organisms a virus can infect.

Question 11

What is tissue tropism?

Answer 11

The specific cells or tissues a virus can infect within a host.

Question 12

Can viruses reproduce outside a cell?

Answer 12

No, they are inert outside cells.

Question 13

What do viruses lack that cells have for replication?

Answer 13

Ribosomes and enzymes for nucleic acid/protein synthesis.

Question 14

What enzyme is unique to retroviruses?

Answer 14

Reverse transcriptase.

Question 15

What percent of viruses have RNA genomes?

Answer 15

About 70%.

Question 16

Are RNA virus mutations frequent or rare? Why?

Answer 16

Frequent, due to error-prone replication.

Question 17

What is a retrovirus?

Answer 17

An RNA virus that reverse-transcribes its genome into DNA (e.g., HIV).

Question 18

What virus causes chickenpox and shingles?

Answer 18

Varicella-zoster virus.

Question 19

What virus causes mononucleosis?

Answer 19

Epstein-Barr virus.

Question 20

What virus is linked to cervical and penile cancer?

Answer 20

Human papillomavirus (HPV) types 16 & 18.

Question 21

What virus causes AIDS?

Answer 21

HIV.

Question 22

What viruses are spread by mosquitoes?

Answer 22

Zika, West Nile, and Yellow Fever viruses.

Question 23

What are the two bacteriophage cycles?

Answer 23

Lytic and lysogenic.

Question 24

What is a prophage?

Answer 24

Viral DNA integrated into the bacterial genome.

Question 25

What is lysogeny?

Answer 25

A dormant viral state where the virus is replicated with the host DNA.

Question 26

What is antigenic drift?

Answer 26

Small mutations in viral genes (e.g., influenza H and N proteins).

Question 27

What is antigenic shift?

Answer 27

Major genetic recombination between viral strains, leading to pandemics.

Question 28

Which influenza type undergoes antigenic shift?

Answer 28

Influenza A.

Question 29

Name 4 ways viruses are classified.

Answer 29

By taxonomy, disease, host, or genome expression (Baltimore classification).

Question 30

What is metagenomics?

Answer 30

Sequencing environmental samples to study unculturable viruses.

Question 31

What’s the difference between acute and persistent infections?

Answer 31

Acute: rapid onset, cleared quickly; Persistent: long-term, chronic or latent.

Question 32

Give examples of persistent infections.

Answer 32

HIV (chronic), Herpes simplex (latent).

Question 33

How can viruses cause cancer?

Answer 33

By disrupting normal cell division and blocking cell death.

Question 34

Which virus is linked to cervical cancer?

Answer 34

HPV (especially types 16 and 18).