Introductory Description of Gene Regulation

How are genes regulated?
They are turned off if there is no need for the enzymes they code for or turned on when the environment changes and the enzymes are once again needed

E. coli in an environment without lactose does not produce the enzymes for lactose digestion. When lactose is present the enzymes for digestion are produced.

Why is this off/on switch important?
Energy is not wasted. It would be similar to having all the electrical appliances in your house on at once. Which of course would be very wasteful. Also unecessary materials would lead to sluggish functioning .

How are the genes for a particular metabolic pathway turned on or off?
On the prokaryote chromosome a combination of genes and regulatory DNA sequences known as the operon accomplishes this.

An example of an operon discovered by Jacob and Monod in E. coli
The lac operon which is off if no lactose is present but can be induced to turn on in the presence of lactose.