If you’re tired after Thanksgiving, don’t blame the turkey! Time to pardon the turkey from the “turkey makes you tired” myth, starting with a bad pun about amino acids (protein letters)…What’s Tweety bird’s fave amino acid? tWiptophan! Tryptophan (Trp) is abbreviated W & you can remember this by saying it like Tweety! You might have heard of it in the context of different bird – yup, Tryptophan’s the source of the “turkey makes you tired” MYTH because Trp is a precursor to the chemical signaling molecules serotonin & melatonin that help regulate mood and sleepiness and stuff. But it’s not that simple!
Let’s start by taking a look at the main player, behind the myth, tryptophan. As I mentioned, tryptophan is an amino acid – and it’s one of the amino acids which, in addition to serving as a protein letter, can serve as a precursor to other things. There are 20 (common) amino acids, each with a generic backbone to allow for linking up through peptide bonds to form chains (polypeptides) that fold up into functional proteins, as well as unique side chains (aka “R groups” that stick off like charms from a charm bracelet). http://bit.ly/aminoacidalphabet
If you look at tryptophan, you’ll see it has a couple of ring things. These ring things will come into play later because they help make Trp “hydrophobic” – basically if something’s hydrophobic, water doesn’t want to hang out with it. And your blood’s mostly water… So in order to travel through the blood it piggybacks on protein called albumin which doesn’t mind hanging out with it. This affects the transport of Trp throughout the body and where/when it can be taken up by cells. So those rings are important – but what *are* they?
Like all molecules, Trp is made up of atoms (individual carbons, hydrogens, etc.). Atoms link up by sharing pairs of electrons – you need 2 for a single bond & 4 for one of the shorter, stronger, double bonds. But what if you don’t quite have enough? You might want to join an electron commune! (otherwise know as resonance/electron delocalization/conjugation). Tryptophan’s a fan of this. Tryptophan is AROMATIC. That doesn’t mean it smells nice, it just means that it has rings and, in the rings, after they’ve “spent” 1 electron each on the bonds to their neighbors they donate their “extra” into a communal shared stock. Those atoms that opt into this commune get to share, and this leads to electron delocalization above and below aromatic rings, kinda like a donut.
Trp’s side chain’s a big, bulky INDOLE w/a methylene (CH₂) linker. INDOLE is BICYCLIC (2 linked rings). It has a 6 carbon (C) BENZENE (similar to the other 2 aromatic amino acids (AAAs) phenylalanine (Phe, F) & tyrosine (Tyr, Y). But Trp has a second “unique” ring we – a 5-membered PYRROLE. Pyrole is classified as HETEROCYCLIC because it has an atom “different” than “the us” carbon. I’m not sure how to abbreviate “yoush” in text, but what I’m trying to tell you is that a nitrogen (N) snuck in. BUT it’s STILL AROMATIC! And bulky and uncharged, so it’s in the category of LNAAs (Large Neutral Amino Acids), a class which includes Tyr, Phe, Ile, Leu, Val, and Met. We’ll get back to this later because all of these guys have to fight for the same doors to get into cells (LNAA transporters).
A while back we looked at some chemical signalers made from the amino acid tyrosine. Tyr gives us dopamine, adrenaline (aka epinephrine) & noradrenaline – collectively called catecholamines), & thyroid hormones. http://bit.ly/adrenalinehormonesetc
Trp also gives us signaling products – melatonin (a hormone) & serotonin (a neurotransmitter), and this is where we get into the turkey myth.
But first let’s recap on what those messenger “job descriptions” mean. Your body has billions of cells and they need ways to talk to one another. Nerves are great if you want to send a signal to one specific place – like to tell the end of a single one of Stephen Colbert’s eyebrows to move up. 🤨 You don’t want to send that “move” message to the whole eyebrow, or the other eyebrow, or definitely not the entire body. To get this level of specificity you have to have a direct connection.
Nerve cells called neurons communicate with other neurons and/or muscle, gland, etc. cells by passing messages really short distances. One neuron releases a chemical called a neurotransmitter (there are lots of different ones, including noradrenaline) into the gap between the 2 of them (synapse) and then receptors on the second one bind that neurotransmitter and relay a message into the cell.
But what if you want to send a message to your entire body? If you see a bear – or a beautiful peak on your chromatograph indicating you’ve gotten a yowza yield from your protein purification prep – you don’t just want to raise an eyebrow. You want your body to stop doing “housekeeping” work like digesting and keeping your fingertips warm and instead focus on doing what you need to do to run away – or run off to fill your friends in on your exciting news!
Unlike the nervous system, which requires all the “wiring” to be laid out, like having one of those “direct” phone lines, which are great if you only want one person to get your message (and no wiretaps allowed!), the ENDOCRINE SYSTEM is more like radio. It sends a message out to everyone, but you can only get it if you have your radio tuned in to the right wavelength. Instead of sending out waves, the endocrine system sends out chemical messenger molecules called hormones from “broadcast stations” called glands and only cells expressing the matching receptors can hear the message and respond (with various responses depending on the type of cell getting the broadcast).
Hormones get secreted into the bloodstream, so they pass by all your cells, but only cells with the right receptors can respond (like having your radio tuned to the right wavelength). These receptors are proteins that are embedded in your cells’ membrane. Like all proteins, the instructions for making them are written in your DNA “blueprint” – so each cell has the instructions and thus could make it if they wanted to but, thanks to lots of regulation, only certain cells do. And they can make more or less at different times to “ramp up” or “calm down” sensitivity & responses to signals.
Trp can be converted into serotonin (5-hytdroxytryptamine (5-HT) which can act as a neurotransmitter that lets brain talk to other cells to regulate things like mood, appetite, sleep regulation, bone metabolism, and GI motility. And, in the brain’s pineal glad, it can be further converted into melatonin (N-acetyl-5-methoxytryptamine). As the “gland” in pineal gland suggests, melatonin is a hormone. It helps regulates sleep & wakefulness
It’s only made in the pineal gland and the retina and a couple others, but not most places in your body because the other places don’t make the needed enzyme (reaction mediator/speed-upper). The pineal gland is a tiny gland in the middle of your brain and it secrete melatonins into blood & cerebrospinal fluid (brain juice). This synthesis & secretion increases during the dark period of day, so you get sleepy at night.
And you get the turkey makes you sleepy myth you probably heard around Thanksgiving. So let’s tackle it. 1st of all, turkey doesn’t have any more tryptophan than other meats (cheese actually has even more). 2nd of all, when you eat Turkey at Thanksgiving, you’re probably eating a lot more than just Turkey – likely you’re also eating a lot of carbs. And this leads to the release of a hormone called insulin. It’s mainly known for its role in telling cells to let in and use glucose (blood sugar) (it’s either not produced enough or not well-recognized in patients with diabetes). But it also has the role of telling cells to let in LNAAs, which, you might remember, in addition to Trp also includes Tyr, Phe, Ile, Leu, Val, and Met. note: some sources also include His in the list
In your blood that Trp’s pretty tied up. Turns out that the indole ring is good at binding to serum albumin, an abundant protein in your blood. So Trp has a hard time getting in, but the others are free-er so they can get into your muscle cells, etc. This leaves Trp with less competition when it gets to the brain and has to cross the blood-brain barrier. It still has to compete with all those other guys here, but it’s starting with an advantage and it likes the transporter here better. So more Trp gets taken in and used. And, although this situation might lead to increased Trp crossing the blood-brain barrier into the parts of your brain where serotonin is made, those parts don’t make the enzymes you need to go all the way to melatonin.
Further exonerating the turkey, the part that does have the needed enzymes, the pineal gland, is actually not protected by the blood-brain barrier. So it’s seeing the same “more competition to get in” blood as the rest of your body. Although it might be even more complicated because your intestines can make some too https://blogs.scientificamerican.com/a-blog-around-the-clock/myths-about-myths-about-thanksgiving-turkey-making-you-sleepy/
Bottom line: The biggest part of the tiredness is probably just your metabolism working really hard to try to breakdown your big meal. And potentially some alcohol consumption… So it’s really unfair to blame the turkey, especially since you’re eating it…
If you’re celebrating Thanksgiving, please do it safely. And please donate to SACNAS, the Society for the Advancement of Chicanos/Hispanics and Native Americans in Science. They do, great, important work, and they deserve our gratitude and support.
more on topics mentioned (& others) #365DaysOfScience All (with topics listed) 👉 http://bit.ly/2OllAB0