Dr. Science, contnued: Proteins

We all know that we need protein in our diets, but what is that stuff, anyway? Proteins are very large molecules consisting of long chains of smaller molecules called amino acids. There can be anywhere from a few hundred to a couple of thousand amino acids in a protein.

There are 20 different kinds of amino acids in proteins. Depending on the sequence of amino acids, the proteins fold up into specific complicated shapes in the cytoplasm (that fluid inside the cell, which is basically salt water, by the way). Each protein has a different function in the cell or in the body.

Some proteins, for example, carry signals between cells or broadcast signals widely throughout the body (such as the hormone insulin, which stimulates cells to take up sugar from the bloodstream).

Other proteins serve as structural elements of the cell or the body -- such as keratin, which is the main ingredient in your hair.

Other proteins, as I noted last time, control what gets in and out of the cell. And, to be more precise, some proteins in the cell membrane transmit signals from other proteins into the cell, without necessarily letting those signaling proteins in.

Some proteins do the contracting that makes our muscles work.

But most proteins are what are called enzymes. They control the chemical processes in the cell -- or occasionally outside of it, such as enzymes in our stomachs that digest particular kinds of molecules in our food. By convention, the names of enzymes end in -ase. If you are living with HIV, or know people who are, you are probably familiar with the names of some enzymes including protease, and reverse transcriptase.

The next subject is the most interesting thing about biology, as far as I'm concerned, and the key to understanding what a retrovirus is. That's the relationship between proteins, and the molecules that embody the genetic code, which are called DNA and RNA.