Tryptophan

     
     Amino acids are composed of an amine group (-NH2) and a carboxylic acid (-COOH) functional group attached to the (α) carbon atom. Each amino acid has a side chain (R group) that are specific to each amino acid and determine whether it is polar or non-polar. This particular side chain on tryptophan is classified as being polar and since it possesses a large hydrophobic indole group attached to its beta (β) carbon, its usually found buried in the hydrophobic core of proteins. 


     Tryptophan is one of the twenty essential amino acids and is needed for normal growth in infants and adults. Since our bodies cannot produce this on its own, we rely on our diet to supplement our needs. Tryptophan also acts as a building block for protein biosynthesis and is a precursor for serotonin (neurotransmitter), niacin (vitamin B3), and auxin (essential for plant body development). Insufficient niacin in the diet can cause nausea, skin and mouth lesions, anemia, and headaches. This production of B-vitamin niacin helps the body produce serotonin which acts as a calming agent and allows our bodies to get a healthy sleep we need to function properly.

     Where do we get tryptophan you might ask? Here is a list of some foods that have this key amino acid; cheese, chicken, eggs, fish, milk, nuts, peanut butter, peanuts, pumpkin seeds, sesame seeds, soy, tofu, and turkey. So the next question one might ask is, "Does the Thanksgiving Day turkey really put you to sleep?" and the answer is yes and no. Yes because turkey does contain tryptophan and this amino acid does produce the vitamin niacin, but no because the reason you feel sleepy is the level of serotonin being elevated due to the niacin, not the actual tryptophan molecule. In order for tryptophan to be changed into niacin, the body needs to have three things; iron, riboflavin, and vitamin B6. Its a reaction in your body due to the tryptophan being introduced into its environment. Therefore, if you eat a lot of turkey your body will produce more serotonin which in turn would make you feel calm and want to nap.  

References:

http://science.howstuffworks.com/innovation/edible-innovations/question519.htm

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002986/

http://guweb2.gonzaga.edu/faculty/cronk/biochem/T-index.cfm?definition=tryptophan