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.