Chapter 33: Viruses

Why is it often more difficult to treat viruses than it is to treat bacterial infections?

Antibiotics used against bacterial infections often target metabolic activities that are specific to the pathogen, but viruses depend on the metabolism and protein synthesis machinery of the host cell for their replication.

Which of the following statements about emerging viruses is true?

Emerging viruses can arise by switching host species or by genome arrangement.

How do enveloped viruses differ from non-enveloped viruses?

Enveloped viruses have a membrane-like outer covering whereas non-enveloped viruses do not.

To identify the cell-surface protein that HIV uses to enter T cells, researchers used antibodies to block different membrane proteins prior to HIV infection. What was inferred from the experiment?

HIV binds to CD4 protein to gain entry to these cells.

Which of the following best describes why there is currently no vaccine for HIV?

HIV evolves very rapidly.

Which of the following is true of the entry of HIV's capsid into a cell?

HIV's capsid entry requires a receptor, co-receptor, and membrane fusion.

Which of the following is one of the two urgent tasks that public health officials first undertake to prevent an outbreak from becoming an epidemic?

Identify the causative agent

Which of the following statements concerning virus entry into all cells is true?

Viruses must always bypass both the cell membrane and cell wall (if present) to enter a cell and replicate.

Which of the following statements about viruses is true

Viruses use cells to produce new generations of viruses.

Which viral genome type requires the fewest number of conceptual steps between infection of a host cell and translation of the viral genetic code into proteins?

(+)ssRNA

Which of the following molecules are always provided by the host cell and are required for replication of all viruses?

ATP

Why are viruses (obligate intracellular parasites) not considered organisms?

All of the Above: Viruses are acellular entities that replicate with the aid of a host cell. Viruses are not alive even though they have a genome, because they are dependent on their host cell to satisfy the five attributes of life. Viruses are not cells and are not made up of cells.

Which hypothesis has been developed to explain the origin of viruses?

All of the Above: Viruses coevolved with cells from the RNA world. Viruses are escaped gene sets from cells. Viruses are the products of degenerate cellular parasites.

How does HIV kill its host?

Kills them indirectly

How have viruses participated in organismal diversity?

Lateral gene transfer

What is the single feature that distinguishes a simple virus from plasmids?

Viruses have a protein coat or membrane-like envelope.

Which lineage of viruses is the most diverse (i.e., contains the largest number of putative species or strains)?

Positive-sense, single-stranded RNA viruses

Considering that there are many RNA viruses and that RNA can be a catalytic molecule, how does this relate to one of the theories for the origins of viruses?

RNA genomes of some viruses descended from genes found in early inhabitants of the RNA world.

Like other viruses, HIV specifically parasitizes helper T cells. What is the role of the helper T cell in mammals?

Responding to invading pathogens

Why did researchers set out to find molecules that would obstruct reverse transcriptase before investigating other viral proteins?

Reverse transcriptase is not a normal part of a human cell's biosynthetic machinery.

Which statement best describes people infected with HIV?

There may be a lag of 8-12 years between the initial infection and the onset of illness, but virtually all people who become infected with the virus will die of AIDS.

Which of the following statements best describes the action of vaccines?

Vaccines contain antigens that stimulate immune system cells and "prime" the immune system for a subsequent infection with a particular virus.

Which of the following statements concerning the production of envelope proteins is true?

Viral mRNAs are translated by ribosomes attached to the rough ER.

Natural selection favors alleles that allow viruses to _____.

replicate within the host

Which of the following statements about the replication of a viral genome is true?

the genome is integrated into the host chromosome during lysogenic growth.