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STUDENT HANDOUT:
STUDENT HANDOUT:
INTRODUCTION:
INTRODUCTION:
Bacteria are not the only microbes that exist. There are also yeast, molds, algae, protozoa and viruses.
Viruses are a rather unique type of microbe. They are acellular entities, which means they are not composed of cells.
Naked viruses consist of a protein coat known as a capsid (Figure 1). The capsid can have one of three shapes (helical, icosahedral or complex shape). Each subunit that makes up the capsid is known as a capsomere. The capsid can also contain glycoproteins.
Figure 1. Capsid shapes. Image from OpenStax’s Microbiology.
The capsid surrounds the virus’ nucleic acid (Figure 2). This nucleic acid can either be DNA (double stranded or single stranded) or RNA (double stranded or single stranded).
Figure 2. Naked virus structure. Image adapted from Wikimedia Commons.
Enveloped viruses are more complex (Figure 3). Surrounding the nucleocapsid (capsid + nucleic acid) is a layer of proteins known as tegument or matrix proteins. The nucleocapsid and tegument are enclosed in a membrane. The membrane contains spike proteins.
Figure 3. Enveloped virus structure. Image adapted from Wikimedia Commons.
Viruses are unable to replicate on their own. In order to do so, they must infect a host cell. For this reason, viruses are unable to survive outside of a host.
Viruses cannot infect just any cell. Viruses demonstrate host specificity. This means that a virus can only infect certain cells. For example, bacteriophages are viruses that can infect only bacterial cells. Animal viruses can only infect animal viruses.
OBJECTIVES:
OBJECTIVES:
Learn what makes up a virus.
Learn why viruses demonstrate host specificity.
PROCEDURE #1: BUILD A VIRUS
PROCEDURE #1: BUILD A VIRUS
We will be looking at four different viruses:
Download the following FILE: Building Viruses.
Using the information from the table above and the cut-outs on your download file, BUILD each of the viruses.
PROCEDURE #2: WHAT CELL WILL YOUR VIRUS INFECT?
PROCEDURE #2: WHAT CELL WILL YOUR VIRUS INFECT?
Download the following FILE: Host Cells.
Looking at the surface proteins and your viruses, determine which virus will infect which cell.
QUESTIONS:
QUESTIONS:
Complete the following table:
2. Based on your virus cutouts and your answer to the previous question, why do viruses demonstrate host specificity?
KEY TERMS:
KEY TERMS:
algae
bacteria
host specificity
icosahedral
mold
protozoa
virus
yeast
SUGGESTED READINGS:
SUGGESTED READINGS:
Where did viruses come from?
Wessner, D. R. (2010) The Origins of Viruses. Nature Education 3(9):37
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