MicrobeWorld

Virus or Bacterium?

Because bacteria and viruses cause many of the diseases we're familiar with, people often confuse these two microbes. But viruses are as different from bacteria as goldfish are from giraffes.

For one thing, they differ greatly in size. The biggest viruses are only as large as the tiniest bacteria.

Another difference is their structure. Bacteria are complex compared to viruses.

A typical bacterium has a rigid cell wall and a thin, rubbery cell membrane surrounding the fluid, or cytoplasm (sigh-toe-plasm), inside the cell. A bacterium contains all of the genetic information needed to make copies of itself—its DNA—in a structure called a chromosome (crow-moe-soam). In addition, it may have extra loose bits of DNA called plasmids floating in the cytoplasm. Bacteria also have ribosomes (rye-bo-soams), tools necessary for copying DNA so bacteria can reproduce. Some have threadlike structures called flagella that they use to move.

A virus may or may not have an outermost spiky layer called the envelope. All viruses have a protein coat and a core of genetic material, either DNA or RNA. And that's it. Period.

Which brings us to the main difference between viruses and bacteria—the way they reproduce.