A compound that contains at least one hydrogen atom and can react with a base to form a salt; a chemical with a pH less than 7. An example of acid in the body is hydrochloric acid (HCl) involved in digestion in the stomach.
One of a group of chemical compounds (organic acids) that have an amino group (NH 2 ); many are the building blocks of proteins.
The unique genetic code found in all living cells (bacteria, viruses, parasites, plants, and animals).

pH

Measurement of the acidity or alkalinity of a substance. A pH of 7.0 is neutral. A substance with a pH less than 7.0 is an acid, with increasing acidity as the pH decreases toward zero. Likewise, a substance with a pH greater than 7.0 is a base (alkali), with increasing alkalinity as the pH moves toward 14.0.