The Function Of Amino Acids And Proteins
To understand the role of proteins in the body, it is important to understand that each type of protein is unique both in structure and function and that it is estimated that over
50,000 unique protein types exist in humans. Each protein type is a unique string of combined amino acids, and if one amino acid is missing, the body cannot make that protein.
Because amino acids are not stored in the body as some other nutrients are, a daily intake of a wide variety of amino acids is essential—which is why there is a class of amino acids called essential. An essential nutrient must be consumed, the body cannot make them and they are essential to life. As an example of the complexity of proteins, hemoglobin—the part of red blood cells that carries oxygen and carbon dioxide—is a string of 146 amino acids. Not all different, but in an exact sequence, like a phone number. While a phone number only contains 10 digits ((555) 555-5555), and there are only 10 possibilities for each digit (0-9), if you are missing one of the numbers from the phone number, or if the number eight on your keypad is broken, the rest of the numbers you have are meaningless. If a cell is trying to build a protein, like an immune system cell, and the amino acid methionine is missing, then that protein is not made. Except for water, almost everything in the body, including enzymes, are proteins.
People eat proteins—whether they be in a carrot, a hamburger, or a slab of tofu—but the body only does business with amino acids. Proteins enter the digestive tract, but only amino acids are absorbed through the walls of the small intestine. That is because digestive enzymes present in the body break down whole proteins into their individual amino acid building blocks—it is these individual amino acids that make proteins the “building blocks of life.” By keeping a dietary intake of rich and varied proteins (and subsequently rich and varied amino acids and nucleic acids), proper protein synthesis and RNA and DNA synthesis can occur in the body. The body is about 16% protein (remember that it is mostly water), and proteins are constantly produced, broken down, and recycled in the body.