Amino acids are a group of organic acids that serve as the fundamental building blocks of proteins and other crucial biological functions and are essential for the growth, maintenance and repair of tissues of all living organisms.
More than 500 amino acids are known to exist, but most organisms, including animals, plants, bacteria and archaea, share the same set of 20 standard amino acids that are used to synthesize proteins. Additionally, two non-standard amino acids are also incorporated into proteins in some species.
Different organisms have different capabilities to synthesize amino acids. For example, while plants can produce all 20 standard amino acids (although in some cases in extremely small quantities), animals (including humans) have completely lost the ability to synthesize some essential amino acids, differing according to the species, through evolution, and are thus dependent on their diets for them.
Humans require 20 different amino acids for various physiological functions. They can be categorized based on how they are obtained into nine essential amino acids, which they cannot synthesize and must obtain from their diet, six conditionally essential amino acids, which can become essential under certain circumstances, such as illness or stress, and five non-essential amino acids, which the body can synthesize.
Environmental pollution, including air pollutants such as ozone and particulate matter, can significantly affect amino acid production, availability and functioning in humans and other organisms in a variety of ways.