The sphingolipids are another major components
of cells. The sphingolipids, you can see, schematically
on the screen. They contain a compound called sphingosine
that we will see how it synthesizes in the minute
and that sphingosine is linked to a
fatty acid shown below in green.
Now the attachment material point
for the sphingolipids is the R that is
shown on the right of this molecule.
So sphingolipids are important,
especially, for nerve tissue and brain.
So very very prominent components.
Sphingomyelin is one of the principle components
of the myelin sheath of nerve cells.
Sphingolipids are comprised of sphingosine,
a fatty acid and a R group, as I said.
So these will all come together
to make the amphophilic substance
that comprises the sphingolipids.
Now the synthesis of these compounds
starts with very simple materials
it starts with the amino acid
serine and palmitoyl-CoA.
These two are joined together to make something
like the sphingosine, as we shall see.
So here is the amino acid serine and
to that we combine a palmitoyl-CoA.
The product to that reaction is dehydrosphingosine, you can
see that we split of a CoA and carbon dioxide in the process of that.
Now dehydrosphingosine can
be converted to sphingosine.
Now sphingosine is not directly
converted into the sphingolipids,
is and it's dehydrosphingosine
that is modified to become dihydrosphingonine,
got a mouth full of names here.
Dihydrosphingonine is reduced in
some reactions, as you can see here,
and a CoA is attached to the molecule.
The product to that reaction is
something called a ceramide.
Now a ceramide is a building backbone for a
sphingolipid, just like phosphatidic acid was a
building backbone for sphingolipid.
The R that you can see on the ceramide at
the bottom is the R that is the upper
portion of the figure on the screen.
Now the R group attachment point is where
the differentiating components of the
sphingolipid will exist.
If the R is phosphocholine
or if the R is phosphoethanolamine we
create one of a class of compounds
called sphingomyelin. So as you can see sphingomyelin
is not one compound but a variety of compounds.
These sphingomyelins comprise the lipid bilayer
of the myelin sheath of nerve cells so
a very very important compounds.
If R is a single sugar then we have
created what we call a cerebroside.
And like its name suggest, cerebroside
are found commonly in brain tissue.
If the R is a complex sugar then we
create what's known as a ganglioside.
This concludes the discussion of the metabolism
of the sphingolipids and the glycerophospholipids.
I hope that I have communicated to you that
these compounds that are found in the lipid bilayer,
like many compounds found in cells,
have roots in very simple molecules,
but drive very complex functions.