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