Imagine a wolf in sheep's clothing. The wolf enters the sheep fold, and, once inside, it takes out all the sheep. This is analogous to the way a virus works. Viruses need a host organism to thrive. A virus is often called an agent because it is not not a cell or an organism. Viruses are the bad guys of the microbial world. Like the wolf, the infective agent enters the host and takes over from the inside.
What makes viruses capable of entering a host, though? Definitely their size and structure help them do this. Click through the tabs below to learn about the specific characteristics of viruses.
Structure and Size
Shape
Host Requirement
About one million virus particles could fit on the tip of this pen
Though viruses have parts, they do not have a proper cellular structure with organelles like eukaryotes. A virus particle is called a virion. A virion consists of a nucleic acid (either DNA or RNA) enclosed in a protein coating called a capsid. They are extremely tiny. They can range anywhere from 20 nanometers (0.00000002 meters) to 300 nanometers (0.0000003 meters), and they can only be seen through an electron microscope. A virus particle can be as much as 50 times smaller than a bacteria.
Viruses come in many different geometrical shapes. The three most common shapes are polyhedral, helical, and binal, as shown in the image. Study these so you can recognize the shapes.
The polyhedral virus has many sides with the same shape that are connected together. The helical virus is shaped like a cylinder with the spiral nucleic acid on the inside. The binal, meaning "two-part," is shaped more like a little bug with a head and legs. There are some viruses that have an irregular shape that don't fit into one of these three categories.
Viruses are parasites of the unseen world and are dependent on a host to provide them with nourishment. A cell is able to survive on its own if it can manufacture proteins using its own DNA. But a virus, even though it contains a nucleic acid, cannot independently make proteins because it lacks other necessary components like ribosomes and enzymes. It must invade a host cell and take over its protein making components to make viral proteins for itself. Unless a virus makes viral proteins using the host's DNA, it cannot make new viruses.
The flu virus infects its human host.
Different virus species attack specific kinds of hosts. Plant viruses attack plants, human viruses attack humans, and bacteria viruses attack bacteria.
Question
If you are a gardener, should you worry about getting the virus that attacks your cucumber plant?
