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Are Viruses Alive?
Current Issues in Biology, Volume 3
Scientific American
PowerPoint® Lectures
Lectures by Greg Podgorski, Utah State University
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Concept Review
One way a virus replicates.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Testing Your Comprehension
The genome of a virus may contain
d) DNA or RNA.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Testing Your Comprehension
Once a virus gains entry into a cell, its next step is to
d) release its genetic material.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Testing Your Comprehension
A rapidly evolving virus
c) has a high mutation rate.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Biology and Society
Viruses have had little impact on human history.
Strongly
Agree
A.
B.
C.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
D.
E.
Strongly
Disagree
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings
Are Viruses Alive?
Interpreting Data and Graphs
Source: UNAIDS AIDS Epidemic Update 2004
If the current 2000–2004 rate of increase is maintained, there will
be 52 million people infected with the AIDS virus.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings