Amino Acids – Amines

00:01 Now, let us move on to amino acids because these are very important species from a biological perspective. Amino acids derive their name from a combination of the amine group and the carboxylic acid group to give a so-called amino acid. Specifically, at the chiral center, which, in this case, is sinister, it is called an alpha amino acid, alpha being a way of explaining or a way of defining a carbon which is one carbon away from a priority group, which in this case, is most likely to be the carboxylic acid.

00:34 In this scenario, all amino acids which are naturally occurring are L, okay, or levorotationary.

00:40 Now, I have to say there are maybe a couple of exceptions to this rule in terms of chemical messengers, one of these being N-methyl-D-aspartate, an amino acid derivative. But, by and large, the ones you will come across and the ones which are found in majority of proteins are going to be levorotationary. So, let’s have a look at amino acids in a bit more detail. And this is important to understand because this influences, in terms of protein therapy and therapy with polypeptide-based drugs, how well, indeed, they’re absorbed.

01:17 If we look at alpha amino acid in its own right and we consider it in its free form, we find that it is actually in dynamic equilibrium with its so-called dipolar structure or zwitterionic form. Hopefully, you can appreciate that when we have an acid component and a basic component on the same molecule, it’s possible for the electron pair from the nitrogen to be nodated onto the hydrogen of the carboxylic acid and actually deprotonate it, thus resulting, as you can see here, in the carboxylic acid carboxylate conjugate base, COO-, and the ammonium, NH3+.

01:52 Dipolar ions are typically found at 7,38 pH. pI is another measure which correlates to the isoelectric point and this is the pH at which the amino acid is actually found in the zwitterionic form and it varies from amino acid to amino acid.

02:16 So, here we have three possible conditions or three possible structures for our amino acid. In the sense that we have this zwitterionic form, where we have protonated NH2 to give us NH3+ and the deprotonated carboxylic acid to give us the conjugate base of the carboxylate.

02:36 At pH 1, which is where we have the most acid, so in other words, we have the most H+ kicking around, both the carboxylic acid and also the amine are protonated. This gives us the carboxylic acid on its own and not the carboxylate and this gives us the NH3+, ammonium.

02:55 Around pH 7, we see we have the zwitterionic form, as we said before, where we have protonation of the NH2 and we have the carboxylic… carboxylate salt. And here, at pH 11, which is a basic pH, that there is insufficient concentration of H+ to protonate the NH2 and we have, by virtue of the amount of hydroxide present, deprotonated the carboxylic acid to give us the conjugate base. Importance in amino acids.

03:28 Well, amino acids are the building blocks of peptides and proteins and proteins are, you know, the basis on which key chemical reactions can and must occur in order for life to exist. They play a crucial role in practically every biological process and there are 20 naturally occurring amino acids. I’ve shown here an example of a hemoglobin protein, which is essential for transporting oxygen and carbon dioxide to and from.

03:55 Amino acids which can’t be synthesised in the body fall into these… into this number here: lysine, histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, valine and arginine. These cannot be synthesised and are actually required by diet and this is usually in the form of meat and dairy products. However, if meat and dairy is not consumed, they can be supplied by a combination of cereal grains such as wheat, corn and rice or legumes, beans and peanuts. Of course, amino acids, as individual molecules,