Friday, November 25, 2005

Thanksgiving Science Post

A common rumor posits that tryptophan in turkey makes you sleepy after eating your Thanksgiving feast. Afarensis explains why this is erroneous.

Anyone who has taken an introductory genetics course is familiar with the tryptophan operon. This (along with the lac operon) is a classic model of transcriptional/translational regulation in prokaryotes. Operons are the combination of regulatory sequences and coding sequences that allow for expression of genes only when the enzymes encoded by those genes are needed. Otherwise, the genes are not transcribed -- this saves the cell energy because it does not need to create proteins when they are not needed. Transcription and translation are coupled in prokaryotes, so we can essentially use the terms interchangeably.

But what is tryptophan? It is one of the twenty amino acids encoded by the genetic code. It is the largest of the amino acids, and is encoded by a single codon (UGG). Being large means it is expensive to produce, so bacteria regulate its production using an operon, only expressing gene when quantities in the cell are low. Tryptophan is also a precursor for the neurotransmitter serotonin which is important in chemical in mood disorders.


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