Viruses
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: July 28, 2016
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Viruses
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Viruses
• Define virus.
• Describe a virus.
What is a virus? Is it even a living organism?
This alien-looking thing is a virus. But is it prokaryotic or eukaryotic? Or neither? Or both? A virus is essentially
genetic material surrounded by protein. That’s it. So, is a virus prokaryotic or eukaryotic? Or neither? Or both?
Viruses: Prokaryotes or Eukaryotes?
Viruses, like the one depicted in Figure 1.1, are tiny particles that may cause disease. Human diseases caused by
viruses include the common cold and flu. Do you think viruses are prokaryotes or eukaryotes? The answer may
surprise you. Viruses are not cells at all, so they are neither prokaryotes nor eukaryotes.
Viruses contain DNA but not much else. They lack the other parts shared by all cells, including a plasma membrane,
cytoplasm, and ribosomes. Therefore, viruses are not cells, but are they alive? All living things not only have cells;
they are also capable of reproduction. Viruses cannot reproduce by themselves. Instead, they infect living hosts, and
use the hosts’ cells to make copies of their own DNA. Viruses also do not have their own metabolism or maintain
homeostasis. For these reasons, most scientists do not consider viruses to be living things.
An overview of viruses can be seen at the video below(https://www.youtube.com/watch?v=L8oHs7G_syI ):
MEDIA
Click image to the left or use the URL below.
URL: https://www.ck12.org/flx/render/embeddedobject/169599
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www.ck12.org
FIGURE 1.1
Cartoon of a flu virus. The flu virus is
a tiny particle that may cause illness in
humans. What is a virus? Is it a cell? Is it
even alive?
Summary
• Viruses are neither prokaryotic or eukaryotic.
• Viruses are not made of cells. Viruses cannot replicate on their own.
• Most scientists do not consider viruses to be living.
Explore More
Use this resource to answer the questions that follow.
• http://www.hippocampus.org/Biology → Non-Majors Biology → Search: Viruses
1.
2.
3.
4.
Briefly describe a virus.
Why are viruses considered parasites?
Describe the outside covering of a virus.
What do the lytic and lysogenic cycles describe?
Review
1. What is a virus?
2. Explain why viruses are not considered to be living.
References
1. Image copyright Kannanimages, 2014. Illustration of a flu virus . Used under license from Shutterstock.com
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