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Biology LibreTexts

10.2: Size and Shapes of Viruses

Skills to Develop

  1. Compare the size of most viruses to that of bacteria.
  2. List 4 shapes of viruses.
 
 

Size

Viruses are usually much smaller than bacteria with the vast majority being submicroscopic . While most viruses range in size from 5 to 300 nanometers (nm) , in recent years a number of giant viruses, including Mimiviruses and Pandoraviruses with a diameter of 0.4 micrometers (µm) , have been identified. For a comparison of the size of a virus, a bacterium, and a human cell, scroll down to how big is... on the CELL'S ALIVE web page.(see Fig. 1A, Fig. 1B, and Fig. 1C)

To view a nice interactive illustration comparing size of cells and microbes, see the Cell Size and Scale Resource at the University of Utah.

Shapes

(see Fig. 1A, Fig. 1B, and Fig. 1C)

a. Helical viruses consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure (see Fig. 2A).

b. Polyhedral viruses consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron ; (see Fig. 2B).

c. Enveloped viruses consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope (see Fig. 2C and Fig. 2D).

d. Binal (complex) viruses have neither helical nor polyhedral forms, are pleomorphic or irregular shaped (see Fig 2E), or have complex structures (see Fig. 2F).

Exercise: Think-Pair-Share Questions

We just learned that most viruses are much smaller than bacteria.

  1. Compare the sizes of viruses and bacteria.
  2. Why are viruses able to be so much smaller than bacteria?

Summary

  1. Viruses are usually much smaller than bacteria with the vast majority being submicroscopic, generally ranging in size from 5 to 300 nanometers (nm).
  2. Helical viruses consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure.
  3. Polyhedral viruses consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron.
  4. Enveloped viruses consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope.
  5. Binal (complex) viruses have neither helical nor polyhedral forms, have irregular shapes, or have complex structures.

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)