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JOANNE STUBBE: We spend a
lot of time looking at--

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all proteins are made from
amino acid building blocks.

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And so one question I get,
and students hate this,

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is, why do I need to know?

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I make them memorize the side
chains of the amino acids.

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Why do I do that?

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Because the side chains
of the amino acids

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are the key to the way all
the catalysts in your body

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function.

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A catalyst simply
enhances the rate

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of conversion of
some small molecule

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into some other small
molecule, and it

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can enhance the rate
of the interconversion

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by 10 to the 15th fold.

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So if you didn't
have that catalyst,

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you couldn't do anything.

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So amino acid side chains
play a key role in catalysis.

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So thinking about the
chemical properties

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of the amino acid side chains
is key to understanding

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all the transformations
in your body.

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So, what is the
pKa of imidazole?

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You remember that?

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Huh?

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GUEST SPEAKER: I don't.

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I don't.

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JOANNE STUBBE: How can
you not remember that?

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[LAUGHTER]

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Anyhow, the pKa of imidazole
is close to seven, OK.

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So those physiological--
everything in the body

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is controlled.

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The pH has to be controlled.

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And so that means that you can
protonate or deprotonate it.

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So knowing that is key to
thinking about how the chemical

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reaction is going to work.

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The amino acid side chains now--

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everybody thought there
were 22 amino acids.

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But now we know almost
all these amino acids can

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be modified once they
get into the protein,

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so that's called
post-transational modification.

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So now we have, probably,
another 250 modifications.

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And one of the modifications
that is essential,

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not for the catalysis
part of proteins,

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but for the structural
part of proteins,

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is hydroxylation of
the amino acid proline.

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So if you don't
hydroxylate proline,

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then you can't make this
molecule called collagen.

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And collagen is a
structural protein.

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It's 25% of all
humans' protein, OK.

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And it's found extracellularly.

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Gram per gram it has
the strength of steel.

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It has very complicated
biosynthetic pathway.

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It has amazing tensile strength.

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It's found in cartilage
and teeth and bone.

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And a key component of collagen
is this hydroxylated proline.

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Because without it, you can't
form the actual collagen

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structure.

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So collagen is this
long-- most proteins,

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if you look at the structures,
they look like little balls.

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They're globular.

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But collagen is a fibrillar
protein, so it's very long.

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it's probably the
longest protein, too.

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It's 3,000 angstroms long.

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And it has three chains
initially, and they

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they're left-handed sort of
helixes but not real helixes,

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and they have to wind
around each other

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to form a right-handed helix.

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This all happens
inside the cell, then

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somehow has to get to
the outside of the cell.

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People are studying that now.

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And then it forms
additional fibrils,

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and they become insoluble.

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And that provides the strength--
the extracellular structures

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provide the strength that
maintain the cell's shape

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and viability of the cell.

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And a key component of all that
is hydroxylation of proline.

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And how did they find that?

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This goes back to,
again, misregulation.

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So, in the 1600s,
or whenever they

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used to sail the ocean
blue with no food,

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they didn't have
enough vitamin C.

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So they didn't have
any citrus fruit.

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So vitamin C has the
vitamin ascorbate,

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and ascorbate plays a
key role in the chemistry

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of allowing the proline
to become hydroxylated.

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So it turns out,
to get the proline

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to be hydroyxlated,
you use, again,

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metal catalyzed reactions.

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So here's iron-2.

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And if that iron-2
reacts with oxygen,

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if it gets oxidized with
iron-3, it can't react.

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So the function
of this vitamin is

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to keep the iron-2
in the reduced state.

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So there's an example.

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People study that.

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Took them many,
many, many years,

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like 200 years later,
when they really

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understand the details of
how this post-translational

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modification actually occurs.

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And we understand a lot
about that chemistry now.

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And this was the first one of
these modifications discovered,

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and now they're finding this
modification everywhere.

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So lots of amino acids turn out
to be hydroxylated, not just

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proline.

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So these modified
amino acids now,

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because the technology we
have is so mind boggling,

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we can find a needle
in a haystack.

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Whereas in the
beginning we were just

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trying to figure out what
the amino acids were,

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now we have very, very
sensitive analytical methods

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which allow us to see all
of these modifications.

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Then the key question
is, what is the function

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of the modification?

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And that's not so easy
in terms of thinking

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about regulation, anyhow.

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And that's the focus of a lot
of people's efforts right now.