Introduction
Proteins are structures created by amino acids. I’m sure most of us have heard about amino acids by now, but what are they and how do they play a role in the development of protein and muscle? Amino acids are the “building blocks” of protein. If we were to imagine building a cabin out of Lincoln Logs, the amino acids would be the logs and the protein would be the finished cabin. In biochemistry we call amino acids monomers (mono meaning a single molecule) that can be bonded to another to form a polymer (poly meaning many molecules). In the case of our analogy, a single log would be a monomer and two or more logs connected together would be considered a polymer.
Amino Acid Structure
The basic structure of an amino acid (known as the backbone) consists of a central carbon atom surrounded by an amino (-NH2), and a carboxyl (-COOH) functional group. If we break down the name of an amino acid, the word “amino” comes from the amino functional group, and the word “acid” comes from the carboxyl functional group which is an acid. Amino acids also have a sidechain attached to their central carbon which is where each amino acid gains its individuality. To complete our backbone, the central carbon has a Hydrogen attached to make four bonds and achieve an octet (the 8-electron configuration that provides stability). See (Figure 1).
Figure 1:
Types of Amino Acids
There are a total of 20 different amino acids, nine of them are Essential Amino Acids (EAAs) (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) meaning that our bodies cannot make them and we must acquire them from food or supplementation. Three of these essential amino acids are Branched Chain Amino Acids (BCAAs) leucine, isoleucine, and valine. BCAAs are of particular importance because they are both essential and are the only amino acids that have the ability to stimulate an anabolic (meaning to build) response. One of these amino acids in particular “leucine” is primarily responsible for signaling this anabolic response1,2,3,4. There is a common misconception that taking a BCAA supplement will build muscle. The reality is that all 20 amino acids are required to undergo muscle protein synthesis (the repair and growth of damaged muscle tissue). All nine EAAs must come from food/supplementation, and the other 11 Non-Essential Amino Acids (NEAAs) must come from food/supplementation or be manufactured from excess EAAs by a process known as de novo synthesis. In summary, while BCAA’s may help to signal an anabolic state, all 20 amino acids must be in sufficient supply to undergo muscle protein synthesis (MPS) and create a complete muscle protein5. See (Figure 2).
Figure 2:
Conclusion
Aside from building and maintaining skeletal muscle, proteins also act as catalysts increasing the rate of chemical reactions for virtually all chemical reactions in the body. They also regulate gene expression and regulate the immune system. Small sequences of amino acids known as peptides can also regulate hormones, reduce inflammation and more.
References:
- Blomstrand, Eva, et al. “Branched-Chain Amino Acids Activate Key Enzymes in Protein Synthesis after Physical Exercise.” The Journal of Nutrition, U.S. National Library of Medicine, Jan. 2006, https://pubmed.ncbi.nlm.nih.gov/16365096/.
- Drummond, Micah, and Blake Rasmussen. “Leucine-Enriched Nutrients and the Regulation of Mammalian Target of Rapamycin Signalling and Human Skeletal Muscle Protein Synthesis.” Current Opinion in Clinical Nutrition and Metabolic Care, U.S. National Library of Medicine, May 2008, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5096790/.
- Son, Sung, et al. “Leucine Signals to mtorc1 via Its Metabolite Acetyl-Coenzyme A.” Cell Metabolism, Cell Press, 6 Sept. 2018, https://www.sciencedirect.com/science/article/pii/S155041311830514X.
- Anthony, Joshua, et al. “Leucine Stimulates Translation Initiation in Skeletal Muscle of Postabsorptive Rats via a Rapamycin-Sensitive Pathway.” Academic.oup.com, The Journal of Nutrition, 1 Oct. 2000, https://academic.oup.com/jn/article/130/10/2413/4686100.
- Wolfe, Robert. “Branched-Chain Amino Acids and Muscle Protein Synthesis in Humans: Myth or Reality? - Journal of the International Society of Sports Nutrition.” BioMed Central, Journal of the International Society of Sports Nutrition, 22 Aug. 2017, https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0184-9.