If you have read How Cells Work, then you are familiar with the inner workings of a typical bacterium and might want to skip this section. Here's a quick summary to highlight the most important points in How Cells Work -- we'll use the common E. coli cell as an example:
- A bacterium is a small, single-celled organism. In the case of E. coli, the bacteria are about one-hundredth the size of a typical human cell. You can think of the bacterium as a cell wall (think of the cell wall as a tiny plastic bag) filled with various proteins, enzymes and other molecules, plus a long strand of DNA, all floating in water.
- The DNA strand in E. coli contains about four million base pairs, and these base pairs are organized into about 1,000 genes. A gene is simply a template for a protein, and often these proteins are enzymes.
- An enzyme is a protein that speeds up a particular chemical reaction. For example, one of the 1,000 enzymes in an E. coli's DNA might know how to break a maltose molecule (a simple sugar) into its two glucose molecules. That is all that that particular enzyme can do, but that action is important when an E. coli is eating maltose. Once the maltose is broken into glucose, other enzymes act on the glucose molecules to turn them into energy for the cell to use. Any cell has enzymes that help it digest food, add to the cell wall, duplicate DNA strands, produce energy molecules, and so on. The E. coli might have thousands of copies of some enzymes floating around inside it, and only a few copies of others. The collection of 1,000 or so different types of enzymes floating in the cell makes all of the cell's chemistry possible. This chemistry makes the cell "alive" -- it allows the E. coli to sense food, move around, eat and reproduce. See How Cells Work for more details.
- To make an enzyme that it needs, the chemical mechanisms inside an E. coli cell make a copy of a gene from the DNA strand and use this template to form the enzyme. The DNA strand contains the templates for all 1,000 enzymes that the bacterium needs to live its life. A section of the DNA strand, called a gene, tells the cell how to manufacture one enzyme. That enzyme, once manufactured, then floats freely inside the cell and does its thing -- it helps the cell perform one of the chemical reactions that the cell needs to live. The process of manufacturing an enzyme from a gene on the DNA strand is amazing -- see How Cells Work for details.
You can see that, in any living cell, DNA helps create enzymes, and enzymes create the chemical reactions that are "life."