These are the 20 biologically active amino acids in humans. In nature, there are more than 100 different types of amino acids to be found.
However, the human uses only 20 of them. Because the human uses only 20 different amino acids out of the many types found in nature, we refer to them as 'biologically active'.
They are 'biologically active' simply because if we consume other types of amino acids, they will not be incorporated into proteins, and are deemed useless or 'non-biologically active'. Consuming some amino acids are are not biologically active can also be harmful (Download)
Amino acids are the building blocks of proteins. An amino acid can chemically bond with another amino acid and so forth, eventually forming a chain. When two or more amino acids are connected they are referred to as a protein. Some proteins are very short in legth. Some are very long. See below.
The sweetener known as Aspartame, is a protein with a length of only two amino acids. Since this protein has only two amino acids, we conveniently call it a di-peptide (di, meaning '2' and peptide, meaning 'bond for proteins'). This is how we make things easier to chat about in the laboratory or hospital while we are drinking lots of coffee (with Aspartame sometimes!)
Now look at the more detailed diagram below to see what things really look like.
This is more what aspartate and phenylalanine look like. When they combine, Aspartame is the end product.
Although Aspartame is a small protein, it fools the human tongue, causing the brain believe it's a sugar. Aspartame is up to 180 times as sweet as sugar, but minus the calories!
This is but one example of how powerful and useful amino acids and thus, proteins are, even the small ones. It's the small ones you have to watch out for! And that's not an exaggeration. Read how some proteins can 'sneak into' the body and cause serious health problems. (download)
Amino acids and proteins can be both useful and equally harmful.
We looked at how short in legth proteins can be when as little as two combine. But how many amino acids can combine in length to make longer and larger proteins?
Human Growth Hormone is a protein which is 192 amino acids in length. It is produced in the pituitary gland of the brain and control growth, metabolism and other functions. Imagine cells in our body, such as those of the pituitary gland having the chemical instructions and power to actually bond (link) amino acids together in order to make proteins such as growth hormone and many others.
Cells that link amino acids together to form proteins must perform perfectly each time they produce a protein. If the cell places even 1 amino acid out of sequence during protein synthesis, unpredictable function of the protein will result.
For example, the defective protein may cause the heart to beat more rapidly, or perhaps increase blood pressure to dangerous levels.
Thousands of amino acids can link together to form extremely large proteins. Titin, the muscle protein responsible for passive elasticity is in the order of 33,000 amino acids in length.
Although there are only 20 different types of biologically active amino acids, they can be combined in virtually endless combinations. Therefore, the types of proteins that can be formed is virtually limitless. And this is why we find thousands of different proteins in the human body.
Amino acids combine to form proteins that act as:
- structural proteins as in the 'scaffolding' in bone
- hormones to regulate metabolism
- antibodies used by the immune system to defend the body
- transporters of oxygen, as in hemoglobin of the red blood cell
- transporters of other proteins which carry substances
- and more (the list is long and fascinating).
Classification of Amino Acids
Amino acids can be placed in the category of either essential or non-essential.
Essential amino acids are those that are "essential" in the diet. In other words,
our metabolism cannot create them.
Therefore, we need to obtain them through foods containing these essential amino acids.
Fortunately, protein-containing foods contain varying degrees of the essential amino acids. During times of
starvation, our body relies on its own protein stores, such as pre-albumin, albumin, and ultimately protein
from sources that it normally shouldn't have to utilize (e.g., muscle tissue, etc.)
Non-essential amino acids are those which can be produced from other amino acids and substances in the
diet and metabolism. During times of need, the metabolism can shift into producing the amino acids that it
requires for synthesizing proteins essential to our survival.
We include a list of essential and non-essential amino acids (above). Click on the inidivual amino acids to learn
more about each one.