True Statements About Virus Structure (Figure 21.5

Figure 21.5 Which of the following statements about virus structure is true? a. All viruses are encased in a viral membrane. b. The capsomere is made up of small protein subunits called capsids. c. DNA is the genetic material in all viruses. d. Glycoproteins help the virus attach to the host cell. Figure 21.5 Complex Viruses. Viruses can be either complex or relatively simple in shape. This figure shows three relatively complex virions: the bacteriophage T4, with its DNA-containing head group and tail fibers that attach to host cells; adenovirus, which uses spikes from its capsid to bind to host cells; and the influenza virus, which uses glycoproteins embedded in its envelope to bind to host cells. The influenza virus also has matrix proteins, internal to the envelope, which help stabilize the virion’s shape. (credit “bacteriophage, adenovirus”: modification of work by NCBI, NIH; credit "influenza virus": modification of work by Dan Higgins, Centers for Disease Control and Prevention)

Figure 21.10 Which of the following statements is false? a. In the lytic cycle, new phages are produced and released into the environment. b. In the lysogenic cycle, phage DNA is incorporated into the host genome. c. An environmental stressor can cause the phage to initiate the lysogenic cycle. d. Cell lysis only occurs in the lytic cycle. Figure 21.10 A temperate bacteriophage has both lytic and lysogenic cycles. In the lytic cycle, the phage replicates and lyses the host cell. In the lysogenic cycle, phage DNA is incorporated into the host genome, where it is passed on to subsequent generations. Environmental stressors such as starvation or exposure to toxic chemicals may cause the prophage to excise and enter the lytic cycle.