20.1 Viruses Answer Key

Question: What is a bacteriophage?

Answer: virus that attacks bacteria

Question: What are viruses?

Answer: They are particles of nucleic acid, protein, and in some cases lipids that can

reproduce only by infecting living cells.

Question: What is a capsid?

Answer: a virus’s protein coat

Question: How does a typical virus get inside a cell?

Answer: The capsid proteins “trick” the cell by binding to receptors on its surface.

Question: What occurs when viruses get inside cells?

Answer: Once inside, the viral genes are expresses. This may lead to the cell’s destruction.

Question: In the visual analogy, why is the outlaw locking up the sheriff, instead of the other way around?

Answer: The outlaw is locking up the sheriff because, like a virus, the outlaw has come in and taken over. The sheriff is basically hostage to the outlaw—as is a cell’s DNA once a virus has entered a cell.

Question: The diagram below shows the lyticcycle of a viral infection. Label the bacterial DNA, host bacterium, viral DNA, and virus. Then, circle the step that shows lysis of the host cell.

Answer: topmost line: virus

second-to-top line: host bacterium

second-to-bottom line: viral DNA

bottommost line: bacterial DNA

circle the step that is labelled with “virus” (shows the viruses burning out)

Question: In a lysogenic infection, how can one virus infect many cells?

Answer: The viral DNA is inserted into the host cell’s DNA. It remains there and is copied

each time the cell multiplies.

Question: How is the common cold like the HIV virus?

Answer: They are both RNA viruses.

Question: What would happen to a virus that never came in contact with a living cell? Explain your answer.

Answer: The virus would never reproduce. Viruses do not have the structures necessary to metabolize, grow, repair damages, or reproduce without a host.