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Biology LibreTexts

10.2: Size and Shapes of Viruses

  • Page ID
    3233
  • [ "article:topic", "authorname:kaiserg", "Virus size", "virus shape" ]

    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 Size and Scale Resource at the University of Utah webpage (see Figure 1A, Figure 1B, and Figure 1C),

    Shapes

    u2fig1a.jpg

    Figure 1A: Sizes and Shapes of Viruses (Animal RNA Viruses)

    u2fig1b.jpg

    Figure 1B: Sizes and Shapes of Viruses (Animal DNA Viruses)

    u2fig1c.jpg

    Figure 1C: Sizes and Shapes of Viruses (Bacteriophages)

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

    u2fig2a.jpgu2fig2b.jpgu2fig2c.jpg

    u2fig2d.jpgu2fig2e.jpg

    Figure 2: Viral Structure (Helical Virus). (B) Viral Structure (Polyhedral Virus), (C) Viral Structure (Enveloped Helical Virus), D: Viral Structure (Enveloped Polyhedral Virus), (F) Viral Structure (Binal) Illustration of a T-even bacteriophage consisting of a head, sheath, and tail.

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

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

    d. Binal (complex) viruses have neither helical nor polyhedral forms, are pleomorphic or irregular shaped (Figure 3), or have complex structures (Figure 2F).

    17778_lores_ebola.jpg

    Figure 3: Electron Micrograph of Filamentous Ebola Viruses Budding from an Infected Host Cell Filamentous, enveloped Ebola visuses (red). Courtesy of National Institute of Allergy and Infectious Diseases (NIAID).

    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)