Current Issues in Biology, Volume 3 Scientific American Are Viruses Alive? Current Issues in Biology, Volume 3 Scientific American

Are Viruses Alive? Concept Review Answering the question “Are viruses alive?” is difficult because a precise definition of what constitutes life is elusive. Viruses exist in a gray area between the living and nonliving. Viruses must replicate within a host cell.

Are Viruses Alive? Concept Review One way a virus replicates.

Are Viruses Alive? Concept Review Historically, research on viruses has focused on how they take over cells or cause disease, with little attention paid to their important role in evolution. Viruses are active agents of evolution and often exchange genetic information with their hosts. Viruses may add their genes to the genome of their hosts, possibly becoming a critical part of the host.

Are Viruses Alive? Concept Review The huge population of viruses, their intimate relationship with their host, and their rapid rates of replication and mutation make them a potent source of genetic innovation. Viruses now need to be studied within the web of life rather than viewing them exclusively as harmful infectious agents.

Are Viruses Alive? The genome of a virus may contain a) DNA. b) RNA. Testing Your Comprehension The genome of a virus may contain a) DNA. b) RNA. c) protein. d) DNA or RNA. e) DNA, RNA, or protein.

Are Viruses Alive? The genome of a virus may contain d) DNA or RNA. Testing Your Comprehension The genome of a virus may contain d) DNA or RNA.

Are Viruses Alive? Testing Your Comprehension Once a virus gains entry into a cell, its next step is to a) enter the nucleus. b) begin protein synthesis. c) begin synthesis of DNA or RNA, depending on the virus. d) release its genetic material.

Are Viruses Alive? Testing Your Comprehension Once a virus gains entry into a cell, its next step is to d) release its genetic material.

Are Viruses Alive? Testing Your Comprehension Viruses can play an active role in the evolution of their host species when they a) lose their pathogenic properties. b) transfer new genes to the host. c) acquire the ability to replicate independently of the host. d) become larger and more complex.

Are Viruses Alive? Testing Your Comprehension Viruses can play an active role in the evolution of their host species when they b) transfer new genes to the host.

Are Viruses Alive? A rapidly evolving virus a) does not mutate. Testing Your Comprehension A rapidly evolving virus a) does not mutate. b) has a low mutation rate. c) has a high mutation rate. d) has a low replication rate.

Are Viruses Alive? A rapidly evolving virus Testing Your Comprehension A rapidly evolving virus c) has a high mutation rate.

Are Viruses Alive? Viruses have had little impact on human history. A. Biology and Society Viruses have had little impact on human history. The intent of the question is to have students extrapolate from the article’s theme of viruses as agents of biological evolution to viruses as agents that shape human history. A contemporary example of a virus that is influencing human history is the AIDS epidemic caused by HIV, especially in Africa where it is reshaping societies. One of many past examples of viruses influencing history is the influenza pandemic of 1918 that killed between 20 and 40 million people worldwide and the decimation of Native American populations upon first European contact. Although certainly not caused entirely by viruses, viruses new to native peoples played an important role in population loss. Strongly Agree Disagree A. E. C. B. D.

Are Viruses Alive? Thinking About Science The genome of influenza virus is made of seven separate segments of RNA. Why would having multiple genome segments instead of one offer an advantage for producing new viral types? a) This increases the rate of mutation in each genome segment. b) If two or more viruses infect a cell simultaneously, the newly replicated viruses may contain a mixture of genome segments from the different infecting viruses. c) The rate of replication of a segmented genome is more rapid than for genomes made of one segment. d) A much larger number of viruses can be produced from infection with viruses with segmented genomes.

Are Viruses Alive? Thinking About Science The genome of influenza virus is made of seven separate segments of RNA. Why would having multiple genome segments instead of one offer an advantage for producing new viral types? b) If two or more viruses infect a cell simultaneously, the newly replicated viruses may contain a mixture of genome segments from the different infecting viruses.

Are Viruses Alive? Interpreting Data and Graphs Source: UNAIDS AIDS Epidemic Update 2004 If AIDS infection rates continue increasing at the rate they did between 2000–2004, then in 2012 there will be ______ people infected with the AIDS virus.

Are Viruses Alive? Interpreting Data and Graphs Source: UNAIDS AIDS Epidemic Update 2004 The reasoning is that in the 4 year interval between 2000 and 2004, there was an increase of 6 million individuals infected with AIDS (~34 million to 40 million). This is an increase of 1.5 million infected individuals per year. Since there are 12 years from 2000 to 2012, this is an increase of 18 million over the starting number of 34 million infections or 52 million infected individuals by 2012. Alternatively, students may see that the graph shows an increase over a 4 year span and the question asks about 2012 – 8 years from 2004. Many will reason that if there were 6 million additional infections in the 4 year span shown in the graph, there will be an increase of 12 million infections in the interval from 2004 to 2012. If the current 2000–2004 rate of increase is maintained, there will be 52 million people infected with the AIDS virus.