Shapes of a Virus: Helical, Icosahedral, Prolate, Complex & Enveloped

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  • 0:05 Viral Shapes
  • 0:40 Helical, Icosahedral,…
  • 3:06 Enveloped and Complex Viruses
  • 5:11 Lesson Summary
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Lesson Transcript
Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Expert Contributor
Maria Airth

Maria has a Doctorate of Education and over 20 years of experience teaching psychology and math related courses at the university level.

Learn about the different shapes viruses can have, such as helical, icosahedral, prolate, complex and enveloped. Find out why one shape is particularly useful from an energetic standpoint.

Viral Shapes

When you're driving around on the road, you see all sorts of different types of vehicles. You've got SUVs, minivans, pickups, motorcycles and 18-wheelers. In the end, they are all a type of vehicle regardless of their shape, size and color. Likewise, viruses have many different shapes as well, and some of their shapes are unique to certain viruses and the things they infect. These shapes aren't just for looks. Like certain types of automobiles, they actually confer a function.

Helical, Icosahedral and Prolate Viral Shapes

Before we get to the nitty-gritty of this lesson, I'd like to point something out. The protective protein shell of each virus is called a 'capsid.' This capsid is made up of protein subunits called 'capsomeres,' which are in turn made of subunits called 'protomers.'

With that in mind, one type of car driving around in the viral world is known as a helical virus. This is a virus that has its capsid shaped into a filamentous, or rod-shaped structure. This type of shape has a central cavity that encloses its nucleic acid. Some of these viruses are short, like a two-door car, while others are very long, like an 18-wheeler. Furthermore, many allow for a lot of flexibility or a lot rigidity depending on how the capsomeres are arranged.

Another type of vehicle shape for transporting viral nucleic acids is called icosahedral. An icosahedral virus is a virus consisting of identical subunits that make up equilateral triangles that are, in turn, arranged in a symmetrical fashion. A special type of icosahedral shape, called a prolate, is a variant of the icosahedral viral shape and is found in bacteriophages.

A lot of viruses are either helical or icosahedral in shape. Many animal viruses, which include those that infect humans, are icosahedral in shape. The icosahedral shape has been shown to be the most optimal way of forming a viral capsid for numerous reasons, but namely due to the fact that it provides the virus with a very stable shape with a lot of room inside for the storage of its passenger, the nucleic acid.

In addition, because the protein subunits that make up the shape are identical, the virus doesn't have to waste a lot of its genome on encoding many different kinds of proteins for its capsid. This leads to conservation of energy and genetic economy. You can sort of liken this shape to the hybrid cars that have the highest fuel economy on the road and therefore save a lot of energy when driving about.

Enveloped and Complex Viruses

Some people apply car wax to the outside of their car for an added layer of protection. Likewise, some viruses like to give themselves an additional layer as well - although this additional layer is not so much for protection but more for ease of infection. These viruses are called enveloped and are viruses that have a lipid bilayer around their protein capsid.

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Additional Activities

Study Materials - To Go

In this activity, students will develop a study tool based on the lesson, Shapes of a Virus: Helical, Icosahedral, Prolate, Complex and Enveloped.


  • Index cards
  • Drawing materials, like markers, pens, and pencils
  • Printer paper or poster board
  • Access to additional research materials (library or internet)
  • Optional art or other supplies chosen by students


1) Students will first review the lesson material. They will also use available research materials to find at least five additional facts related to the lesson material to include in this activity.

2) Next, students will design a study tool that can be used to learn the shapes of viruses as well as any general information about each type of virus covered. Students should design their study tools for use by same-age or same-grade students such as themselves (they may want to/need to use the study tools themselves). Some ideas for study tools are:

  • Flashcards (Index cards could be used to create mini-flash cards. The front of the card could show the shape of a virus, while the back of the card could provide information about viruses with that shape.)
  • Informative poster (Using poster or printer paper or presentation software, students could create a simple visual aid, like a chart.)
  • Outline (This common study tool helps students to focus on the details of the information given.)

3) The study tool must include:

  • All of the terms given in the lesson
  • At least five facts not included in the lesson

4) After students have completed their study tools, they should find someone to use them. Users could be classmates, family members, or friends. Students should ask for feedback about their individual study tools and adjust them according to the feedback given.

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