Tobacco Mosaic Virus: Structure and Function

Lesson Transcript
Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

Tobacco mosaic virus is commonly found in tobacco plants, appearing in a 'mosaic' of discoloration patches. Learn the structure and function of this virus, including its effects on agriculture. Updated: 12/13/2021

Tobacco Mosaic Virus Basics

When you hear the word virus, what comes to mind? Sniffles and a sore throat? Or, maybe you think of a different kind of virus that can erase files and wreak havoc on your computer. But did you know that humans and computers aren't the only ones who have to worry about viruses? Believe it or not, plants can get viral infections just like people can, and they cause a great deal more trouble than a case of the sniffles. Continue on to learn more about the first virus, which was discovered more than 100 years ago.

Tobacco mosaic virus received its name because the plants that it infects often show patchy discoloration, giving them a mosaic-like appearance. This viral villain is bad news for your green plant friends. If you haven't guessed by its name, it obviously infects tobacco plants, but it can infect many other plant species as well.

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  • 0:03 Tobacco Mosaic Virus Basics
  • 0:55 Structure
  • 2:28 Function
  • 3:27 Importance
  • 3:59 Lesson Summary
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The structure of tobacco mosaic virus is impossible to see with the human eye because it is very small - approximately 300 nanometers long. This means that 3,000 tiny viruses would fit in a single millimeter.

The basic makeup of all viruses is pretty much the same. First, they all contain a genome, which carries their genetic blueprint. Of course, we humans have a genome too, but ours is the recipe for making a human, and a virus' genome is the recipe for making a virus.

Tobacco mosaic virus' genome is different from ours in other ways, too. Humans have a genome made from a molecule called DNA, but tobacco mosaic virus' genome is made from DNA's cousin, a molecule called RNA. The human genome is also split into many chunks called chromosomes. However, tobacco mosaic virus has a genome that is attached together in one strand.

The second thing all viruses need is a capsid, or a container to hold and protect their genome. Tobacco mosaic virus has a helical-shaped capsid made of more than 2,000 copies of a particular protein. Imagine 2,000 beads on a string that loops around and around like a tight spiral staircase. The tube-like structure that is formed is similar to tobacco mosaic virus' helical capsid.

So, in a nutshell (which is actually quite like a capsid!) the structure of tobacco mosaic virus is an RNA genome inside a helical capsid.


A virus has a simple life cycle: Replicate. Spread. Repeat.

All viruses need a host to replicate, so successful spreading means infecting a new host. Only then can the cycle repeat itself.

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