Alanine, cysteine, aspartic acid, glutamic acid, phenylalanine, glycine, histidine, isoleucine, lysine, leucine, methionine, asparagine, pyrrolysine, proline, glutamine, arginine, serine, threonine, selenocysteine, valine, tryptophan, tyrosine. These are 22 proteinogenic amino acids that make up pretty much every protein inside your body. They're the reason you can think, digest food, and contract your muscles. Hell, without them, multicellular life is impossible.

I fell in love with them when I took a molecular science class in my high school. One of the "dreaded" topics that we had to cover was the 20 main amino acids that made up most proteins. I remember in my freshman biology class about amino acids when we had to figure out the amino acid sequence when DNA was transcribed into mRNA, which was then translated into a polypeptide. We used tables like the one below:

I was presented with slides of 20 amino acids, concerning their orientation in space as well as what makes them so special. So what exactly is an amino acid?

Amino acids are named accordingly because they contain an amine group (-NH2) and a carboxylic acid group (-COOH). The central carbon atom has an R group, which means it is a variable group. It can literally be anything, ranging from another hydrogen to complex carbon chains, rings, and can even include other elements such as nitrogen or oxygen. Two amino acids contain sulfur, and one even contains selenium. It's frankly magical when you understand so much of how biochemistry works when you understand that protein function is completely dependent on a proper amino acid sequence and orientation in space. Even one amino acid substitution or change can be devastating for the body. Take sickle-cell anemia for instance. When even one amino acid is changed to the wrong one, red blood cells suddenly lose their slightly indented shape and become sickle-shaped, which causes anemia.

I love them for their immense biological significance and role, which frankly rivals that of DNA and RNA in terms of importance. However, it is incorrect to say that all biological functions would be nonexistent without amino acids. What's quite interesting is that some RNA in the ribosome can act as an enzyme to bond the amino acids together to form a new polypeptide chain. Regardless of that, proteins have an immense role and are the reason we can think, see, fight off infections, and let our cells communicate with each other.

Now I keep mentioning that there are 22 proteinogenic amino acids when I was taught only 20 of them. The other two are much less commonly found in cells but are found in all domains of life (you don't need to know this for the MCAT, don't worry.)

I'm quite thankful to my molecular science teacher for introducing me to the foundations of proteins such that I can recognize them on sight and understand just how a protein works, where the active sites could be, and what its functional role could be in the body. It's because of amino acids that I gained a deeper appreciation of molecular biology and learned the basics of organic chemistry, which I'd never trade for anything.