HAZEL SIVE: I want to extend
this notion of information
into the proteins.
So proteins, you remember, are
the polymer of amino acids,
and they have quite
a lot of similarities
in their notion of
information coding
than the nucleic acids do.
They have a kind of a
backbone, and then they
have information that is
associated with the backbone.
When we write proteins,
we designate N or an NH2
or amino as one end of
the protein molecule.
And then we write amino acid
one joined to amino acid
two, amino acid three.
And then we have C
or COOH or carboxy,
and that would be
at the other end.
The amino acids
are joined together
by a peptide bond, covalent
bonds, between the amino group
and the carboxyl group
of the amino acids,
and this NC bond will
form a kind of a backbone,
similar to the nucleic acids.
Not the same at
all, but the notion
is similar, as I'll
show you in a moment.
The amino acid order
is relative to the two
ends of the molecule.
So there is polarity
to proteins that
is based on the amino
and carboxy ends,
and is also based on
the amino acid order.
And we can draw a
parallel, again,
to nucleic acid structure.
The carboxy amino acid
is the last added,
and the next one will
add on to the carboxy end
so that the carboxy end has
the last amino acid added,
and the next adds
to this carboxy end.
A little compressed down there,
but let's go to the slide.
The first thing I
want to show you
is that proteins have got two
different ends, an amino end
and a carboxy end, with
the amino acids arrayed
between those.
And then if we look at
the protein polymer, two
different amino acids
here, glycine and alamine,
circle the alpha carbon
on these, joined together
to make a peptide bond,
which I've circled in blue,
and leaving a free amino
end on the first amino acid
of the polymer and
a free carboxyl end
on the last amino acid.
And if a new one
were to add-- this
is just a dipeptide,
this very tiny protein.
If the next amino
acid were to add,
it would add where I've arrowed
the incoming next amino acid.
When we write proteins, we
write with the three or the one
letter amino acid code.
We always, and this has another
parallel to nucleic acids--
we always write the amino
end and the carboxy end.
We never get too old
to write the amino acid
and the carboxy
end onto a protein.
So here I've got a couple
of example peptides,
little tiny proteins, with
their amino and carboxy ends
indicated.
And here, again, the
direction of polarization.
The order of the amino
acids is the information.
The polarity of the amino acid
chain, the N and the C ends,
shows the first to the
last amino acid added
and the direction to
read the information.
If we compare the proteins
and the nucleic acids,
there is an order
of monomers that
can be read in a
defined direction,
and that defined direction
is the information.
In the nucleic
acids it's the order
of the nucleotides from
five prime to three prime.
In the proteins, it's
the order of amino acids
from the free amino to
the free carboxy terminus.
And so for your
last assignment, I'd
like you to go and practice
looking at protein polarity
and how you write
this and which is
the first and the
last amino acid.
