Viruses

Most of us at one time or another have had colds or the flu, and we are especially vulnerable during the cold and flu season. The symptoms -- fever, congestion, coughing, sore throat -- spread through offices, schools and homes, no matter where in the world we live.

Colds and flu (influenza) are caused by viruses. Viruses are responsible for many other serious, often deadly, diseases including acquired immunodeficiency syndrome (AIDS), Ebola hemorrhagic fever, infectious hepatitis and herpes. How can viruses cause so much trouble?

What makes us so vulnerable to them, and what makes them spread?

In this article, we will explore the world of viruses.

We'll talk about what a virus is, what viruses look like, how they infect us and how we can reduce the risk of infection, and you'll learn why you feel so miserable when a cold virus attacks your body!

The flu virus - Photo courtesy CDC

What Is a Virus?

A cell is a stand-alone living entity able to eat, grow and reproduce. Viruses are nothing like that. If you could look at a virus, you would see that a virus is a tiny particle. Virus particles are about one-millionth of an inch (17 to 300 nanometers) long. Viruses are about a thousand times smaller than bacteria, and bacteria are much smaller than most human cells. Viruses are so small that most cannot be seen with a light microscope, but must be observed with an electron microscope.

A virus particle, or virion, consists of the following:

  • Nucleic acid - set of genetic instructions, either DNA or RNA, either single-stranded or double-stranded
  • Coat of protein - surrounds the DNA or RNA to protect it
  • Lipid membrane - surrounds the protein coat (found only in some viruses, including influenza; these types of viruses are called enveloped viruses as opposed to naked viruses)

Viruses vary widely in their shape and complexity. Some look like round popcorn balls, while others have a complicated shape that looks like a spider or the Apollo lunar lander.

Unlike human cells or bacteria, viruses don't contain the chemical machinery (enzymes) needed to carry out the chemical reactions for life. Instead, viruses carry only one or two enzymes that decode their genetic instructions. So, a virus must have a host cell (bacteria, plant or animal) in which to live and make more viruses. Outside of a host cell, viruses cannot function. For this reason, viruses tread the fine line that separates living things from nonliving things. Most scientists agree that viruses are alive because of what happens when they infect a host cell.

Article Source: HowStuffWorks.com

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