Pima Air and Space Museum , Tucson, Arizona

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Viruses and Bacteria…

What exactly is a virus? How does it differ from bacteria?

Bacteria and viruses can cause many diseases, but the distinction between the two forms of microbes is often vague and confused.

One of the main differences is the size. Compared bacteria, viruses are normally much smaller in size. The largest viruses are about the same size as the smallest bacteria.

One other striking difference is in the structure of the two types of microbes. Bacteria are complex structures, compared with viruses.

The structure of a single bacterium consists of a rigid cell, and a thin flexible membrane, which surrounds the cytoplasm, a fluid within the cell. A single bacterium has all the genetic data, the DNA, required to copy itself. This information databank is contained within the chromosome. There are other tiny portions of DNA, called plasmids which float around in the cytoplasm. To maintain the degree of complexity, there are also working tools, called ribosomes, which are essential for the bacteria to reproduce.

By comparison, a virus has a protein coat and a central core of DNA or RNA, the genetic material needed for reproduction. Sometimes it has an outer spiky layer called the envelope.

Two types of viruses

In comparison to bacteria, which have all the genetic blueprint and tools required to reproduce themselves, a virus needs to invade other cells in order to reproduce.

A hole is cut in the cell wall. The virus then injects its genetic material into the host cell. It then uses the hosts genetic machinery and instructs it to make new parts of the virus. These parts are then assembled together to form new viruses.

Here is an animated version of the sequence of events….

Now the really bad news occurs! These viruses can then break out of the host cell and each one can invade another new host cell. In this way the virus can replicate itself in increasing quantities every hour. Multiplication combines with a cascade effect, and an exponential rise of viruses.