So, you’ve made your way to Neurochemistry! We, The Chemistry Club, would love to give you an insight on the chemistry in- you guessed it- your brain! Here, we’ll talk about the chemicals in your brain- mainly your neurotransmitters and their receptors, the reactions that take place and the effects they have on you.
Neurotransmitters
Neurotransmitters mainly come in small molecules and neuropeptides. In simple words, neurotransmitters are the body’s chemical messengers. These are chemicals released by vesicles in a presynaptic neuron that cause electrical impulses to carry over through synapses. (For those of you who don’t know what a synapse is, it’s the gap between two neurons).
The small molecule neurotransmitters can be amino acids or biogenic amines. But first, let’s talk about amino acids. Amino acids are the monomers, or basic units, of proteins. They all have the same basic structure- a central carbon atom, an amino group, and a carboxyl group. Lots of big words, let’s break it down- amino groups have an NH2 group, and a carboxyl group contains a COOH group. These are known as functional groups, and they are integral to the chemical characteristics of the compound. The picture below shows the structure of an amino acid. Next up, biogenic amines- these are neurotransmitters with amine groups but no carboxyl groups. An amine group is another functional group that contains a basic nitrogen atom with a lone, or unbonded, pair of electrons. Three well-known examples of these are adrenaline, dopamine and serotonin.
Neuropeptides are another kind of neurotransmitter- they’re made up of 3 or more amino acids, and are larger than small-molecule neurotransmitters. Some of these include the neurotransmitters known as endorphins, which relieve stress and pain.
That’s for our neurotransmitters. However, the function of these neurotransmitters is incomplete without the protein molecules called receptors. Receptors are located on the postsynaptic neuron and are mainly of two types: Metabotropic receptors and ionotropic receptors.
Ionotropic receptors are protein complexes. Protein complexes are formed due to non-covalent interactions between protein molecules. So what do these receptors do? Ligands* bind to these receptors due to intermolecular forces such as dipole interactions**, hydrogen bonding*** and attraction between ions. Receptors are specific to ligands and change their shape after the ligand binds to them which causes the channel to open or close, hence, allowing signals to pass through.
Let’s look at an example: Gamma-aminobutyric acid (GABA) is a neurotransmitter that helps in controlling anxiety and so allows us to feel better. GABA binds to its ionotropic receptors, which are made up of five protein molecules. These molecules are arranged in a way such that they form a channel. Binding causes this channel to open and allows signals to pass through.
On the other hand, the ion channel is indirectly opened or closed when talking about Metabotropic receptors.
Well, this is the end of our neurochemistry issue! Thanks for reading until the end, and we hope you gained some knowledge about how chemistry manifests in neurotransmitters and their receptors. Keep an eye out for our next article!
P.S. This article had some complicated terminology, so if you’re confused, have a look at these terms.
Ligands*: Ligands are molecules or ions that have a lone (or unpaired) pair of electrons, which they donate to form covalent bonds.
Dipole-Dipole Interaction**: Some atoms are more electronegative than others ( meaning that they hold a larger share of electrons in a covalent bond) giving them a partial negative charge, and the other atom(s) a partial positive charge. This causes a dipole to form, and when two dipoles interact, positive attracts negative and vice versa. This makes the structure stronger by increasing the forces of attraction between molecules.
Hydrogen Bonding***: When hydrogen bonds with extremely electronegative elements (Nitrogen, Oxygen and Fluorine), it forms a very strong dipole- so strong it gets a name of it gets a name of its own. It is a kind of dipole-dipole interaction and functions on the same concepts.
By : Mythri Subash and Maheshi Parwani
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