00:02
In another set of these
lectures, I've talked about the
importance of heme for carrying
oxygen within hemoglobin.
00:08
In these set of lectures, I'll
talk about how that heme is made
and how the iron in the heme is
transported and stored in the body.
00:17
Now, heme is as you've seen in the other
lectures, a flat, planar structure
that contains a porphyrin ring with
an atom of iron at its very center.
00:26
The ring structures that hold the iron
can serve as a sink for electrons
and this can be valuable also for
the process of electron transport.
00:35
The ring also enables
the carrying of oxygen
which is what happens
inside of hemoglobin.
00:40
So, hemes are usually found
attached to proteins.
00:43
That's true whether they're
in the electron transport
system or they're contain within
a hemoglobin or myoglobin.
00:49
The examples, of course, include
these proteins: hemoglobin,
myoglobin and the cytochromes of
the electron transport system.
00:56
The names of the cytochromes in
the electron transport system
come from the hemes
that they contain.
01:01
Cytochrome a, for example
contains heme a.
01:05
The ring structure that's found
in the hemes of hemoglobin,
myoglobin and cytochromes is
also found in the chlorophyll.
01:13
And in the chlorophyll, the ion is
replaced with the magnesium at its center.
01:17
The cobalamins, also known as
vitamin B12, have a cobalt
at their center instead
and we can see that here.
01:24
Now, the structure and function of hemes
is related to their planar structure.
01:28
And we can see that the various
hemes have a very similar central
structure as we see in Heme A,
Heme B , Heme C and Heme O.
01:37
And we see that the primary differences
of these different forms of heme
are due to alterations on the
outer part of the molecule.
01:43
These have little effect on the function
of each of the individual hemes.
01:48
Heme A is found as part of the
complex IV of the electron
transport system and it’s the
part where oxygen is reduced.
01:56
Heme B is the most common type that
we see and it's found in hemoglobin,
myoglobin, peroxidase enzymes and cycloxygenase
enzymes for making prostiglandins.
02:05
Other proteins that contain heme B include
the P450 hydroxylation system of the liver
and the nitric oxide synthase system that
we've talked about in other lectures.
02:15
Now heme C is found as the name
would suggest in cytochromes C,
a very important protein in the
electron transport system.
02:22
And it links to the protein via
cysteines, the sulfur side chains.
02:27
Heme O functions in bacterial
oxygen reduction very much
like the heme A does where the
complex IV reduces oxygen.