L ... dopa
- Jan 14
- 4 min read
Tavishi
This is the first year that I haven't done science bowl since 2019, and it's actually really sad. I didn't realize I would miss my competitive nerd buzzing sport this much, but it is where I have obtained most of my closest friends. I sound like someone who peaked in high school, but goddamn it, I peaked in high school.
Anyways, the science bowl community was so tightly-knit that it unironically had its own slang. For example, the term "biking" is used for cheating, and "stock" signifies content that comes up frequently. And then, further within the community, there are little inside jokes specific to schools or certain tournaments.
Like at my school, we have opsonisation (boo Akhil.)
Anyways, stock content in science bowl includes L-dopa and Parkinson's disease and dopamine. I know of several people who can tell me these three are linked, and that if they hear one of these words, they think all three instantly, but very few who? actually understand what L-dopa is.
L-dopa is one of the precursors to dopamine. Something that has long fascinated me is how every substance in the body can be made from something else. The intricacies of the body's processing systems is so cool to me, and this is where I also ended up getting interested in the process of bioremediation.
Back on topic, L-dopa forms originally from tyrosine. Tyrosine is easily my favorite amino acid:
Anyways, tyrosine is the precursor to so many different crucial molecules in the body, which is why it is so cool and also so crucial. Tyrosine itself is synthesized from phenylalanine, but phenylalanine is so basic and boring, and I prefer my amino acids more polar and exciting. Phenylalanine is one of the 8 essential amino acids (amino acids that cannot be synthesized in the body, but rather, must be consumed. Other amino acids can be synthesized from essential amino acids by adding a few extra groups).
Phenylalanine is tyrosine without its hydroxyl hat. Tyrosine is produced when acted upon by the enzyme phenylalanine hydroxylase, which takes a hydroxyl from tetrahydrobiopterin, a cofactor, and gives it to phenylalanine instead, producing tyrosine!
When this conversion isn't happening enough, a buildup of phenylalanine occurs, producing a disorder called phenylketonuria. This disorder is generally caused by a lack of function mutation in the phenylalanine hydroxylase gene (PAH).
Back to tyrosine! This whole post is just a ramble because it is essentially me explaining a bunch of different biochemical pathways and getting sidetracked. This is why I am always late when walking somewhere, because instead of just following the normal path, I start walking behind a dog, or decide to stop to look at a ladybug.
Tyrosine can produce a lot of different things, including the thyroid hormones. However, today, we're talking about the catecholamine production. Catecholamines are neurotransmitters derived from tyrosine.
L-tyrosine, apparently, does not have enough hydroxyl hats, so it receives yet another one! With the help of oxygen and a donation from tetrahydrobiopterin (popular hat seller), tyrosine hydroxylase grants yet another hat to L-tyrosine, producing L-dopa (long name is L-3,4 dihydroxyphenylalanine). The long name roughly translates to left handed phenylalanine with two hydroxyls on the third and fourth carbon.
We will circle back to why L-dopa is science bowl stock shortly! Now that we have produced the infamous L-dopa, the next step is to make dopamine. The difference between L-dopa and dopamine is that L-dopa gets amputated, losing its carboxyl group. The enzyme doing the amputation is DOPA decarboxylase, and it has a little friend that helps it position itself just right to get the carboxyl group off easily. Aforementioned little friend is vitamin B6, or pyridoxal phosphate.
A carboxyl group is -COOH, or a carbon double bonded to an oxygen and single bonded to a hydroxyl. Now, we get dopamine!
Dopamine is a neurotransmitter involved in motor function, reward, learning, emotion, and some functions within the rest of the body. It is received by 5 different receptors, D1, D2, D3, D4, and D5. All five of these are G-coupled protein receptors, which means that dopamine binding results in the activity of the G protein. G protein causes a cellular cascade involving the conversion of ATP to cAMP by adenylyl cyclase. cAMP is a very important second messenger, that basically goes around yelling at the cell to get the shit done that it needs. The enzyme that catalyzes this change from ATP to cAMP is adenylyl cyclase, and its activity is modulated by G proteins. Some GPCRs increase adenylyl cyclase activity, or Gs receptors, and some decrease that activity, or Gi receptors. There's also G-alpha-q receptors, which are weirdos with a different pathway.
Anyways, dopaminergic neurons are neurons which release dopamine. Parkinson's disease is the degradation of these neurons in the substantia nigra. When these neurons are degraded, the release of dopamine decreases. How is this solved? By adding L-dopa to the brain.
You'd think that low dopamine levels mean that you should just give a patient dopamine, but you neglect to reflect upon the fact that dopamine is incapable of entering the brain from the blood. Dopamine cannot cross the blood-brain barrier, but L-dopa can.
So when L-dopa is added to the brain, dopamine gets produced.
In the end, L-dopa can only do so much. As with many treatments for neurodegenerative diseases, it's a bandaid covering the wound rather than treating it.
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