Tobacco mosaic virus is not why cigarettes are unhealthy for humans; rather, it is an interesting virus to study. This lesson will give the real facts on its structure and function.
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.
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.
Tobacco mosaic virus can spread by direct plant-to-plant contact where it enters through tiny holes in the plant. If a plant is injured, this makes it even easier for the virus to get inside. It's just like when you have an open wound - you need to keep it clean and covered up because the open sore makes you more susceptible to infections.
The virus can also be carried from plant to plant by a carrier organism. Imagine a tiny insect walking on an infected plant and then walking on a neighboring healthy plant. Those tiny feet could easily track some viral particles on the new plant (and some insects have lots of feet). Additionally, seeds can also become contaminated, creating new plants that are already infected with tobacco mosaic virus.
Tobacco mosaic virus can have a negative effect on the agriculture industry. Depending on the species of plant that it infects, it can cause stunted growth and poor health, eventually leading to death. This persistent virus has been known to live for half a century in dried, dead pieces of plant - so once it shows up, it isn't easy to get rid of. Just like humans trying to prevent the spread of the cold or flu, farmers and others who handle plants must wash their hands and tools often to prevent spreading the virus.
Tobacco mosaic virus is a virus that infects plants, including tobacco. It has an RNA genome inside a helical capsid. It can be spread from plant to plant, passed along by a traveling insect or other carrier, or passed through contaminated seeds. It does not infect humans or animals, but it can cause problems for the agricultural industry. Good hygiene can prevent viral spread.