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PROFESSOR: Hi.

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In this clip, we're going to go
through problem two of the

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transcription and translation
unit.

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We're also going to review all
of the information you would

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need to fill out problem
one, the table.

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If you haven't tried these
problems yet on your own,

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please pause the video now and
try them, and then come back

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and watch this explanation.

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OK.

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So here we have, as in problem
two, the double stranded DNA.

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Now, this is a piece of the
eukaryotic genome, and so this

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DNA is in the nucleus
of the cell.

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Now what we're going to do is
we're going to go through

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transcription and translation
with this gene.

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So the first thing we need to
do is we need to figure out

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where we want to start
transcription and in what

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direction we want to go and what
strand we want to use as

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our template.

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So in the problem, we're given
our promoter region and we're

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given that our transcription
starts right here at this

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arrow and moves in
this direction.

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So we know where we're starting
and what direction

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we're moving in.

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All transcription will proceed
reading a template in the

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three prime to five prime
direction and will polymerize

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the RNA made in the five prime
to three prime direction.

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So what we need to do now is
figure out what strand is

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going in the three prime to five
prime direction and the

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direction that we're going
to be transcribed.

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So that means that this strand,
which is going from

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three prime over here down to
five prime at the end, this is

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going to be our template
strand.

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So our template strand is going
to be at the bottom.

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OK.

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So when our RNA polymerase
starts, it's going to be

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reading this template strand
and adding nucleic acid,

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adding nucleotide triphosphates,
or NTPs, one by

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one together to make the RNA.

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Now it's going to add these
together by adding a

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phosphodiester bond in between
all of the monomers.

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So we're going to start
our transcription.

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And basically, what I need
to do is just use the

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complimentary base pair
to my template strand.

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So I'm going to write
it out here.

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So I've done a lot of
transcription here.

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Now where am I going to
stop my transcription?

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I'm not going to stop
just randomly in

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the middle of nowhere.

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What my RNA polymerase is going
to do is it's going to

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stop when it gets to the end of
this terminator sequence.

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So I'm going to keep
transcribing until I get to

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the end of my terminator here.

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OK.

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So this is my RNA strand.

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And as I said before, we're
going to polymerize this mRNA

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in the five prime to three
prime direction.

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OK, we've got our mRNA.

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Since this is a eukaryotic cell
and the mRNA right now is

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in the nucleus, what we need to
do is transport it out of

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the nucleus and into the
cytoplasm where it will be

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translated by a ribosome.

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Now what the ribosome is going
to do is it's going to take

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this mRNA, which is a message
that encodes the sequence of

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amino acids that we need to
put together to make the

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protein, and we're going to take
this message and we're

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going to find a place to
start translation.

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So what the ribosome is going
to do is it's going to start

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at the five prime end of the
template and read towards the

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three prime end of
the template.

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It's going to read until it
gets to a start codon.

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The start codon is AUG.

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So this is where we're going
to start, and AUG encodes

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methionine.

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We're then going to read in
three base pair codons down

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from the five prime end of our
template to the three prime

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end of our template.

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And so we're going to keep
going in this translation

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until we reach what's
called a stop codon.

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Now there are three
stop codons.

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Stop codons are UAA,
UGA, and UAG.

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So if when my ribosome finds any
of these three codons in

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frame, it's going to stop.

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So I get all the way down here
before I hit a stop codon on

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this transcript.

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So what my ribosome is going
to be doing as it's reading

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these codons is it's going to
insert amino acid by amino

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acid, pairing them together
with a peptide bond.

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So we've got methionine bonded
to histidine, tyrosine,

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leucine, and so on
and so forth.

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OK, so this is the protein chain
that's encoded by this

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gene in the DNA.

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And in proteins, we always
synthesize from the N terminus

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to the C terminus.

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OK, so we've gone through both
transcription and translation.

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Now what we want to do is we
want to take into account what

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would happen if we had a
mutation in our sequence.

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So in this case, in this
problem, we're going to insert

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a base pair right here.

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So we're going to insert
an extra T here

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and an extra A here.

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Now, if this is happening in
the DNA, when our DNA is

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transcribed to make our
RNA, what's going to

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happen to the RNA?

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Well, we're going to also add
the corresponding base into

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our RNA, so we're going to
have an extra U here.

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So in addition to only adding
one nucleotide in our RNA,

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this is also going to throw
off our frame that we're

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reading when our ribosome
is reading our RNA.

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So instead of the frame that we
had previously, we're now

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going to have a new frame.

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So it's going to start at the
same start codon and then read

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this codon just as normal, but
then this U will make UUA and

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then will read in codons
of three from there.

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So again, I need to translate
until I hit a stop codon.

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And so the stop codon is going
to be different in this case,

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because this stop codon
is no longer in frame.

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I need to find an in
frame stop codon.

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And the first stop codon that I
hit is going to be this you

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UAG right here.

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And so our new protein sequence
is now going to be N

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terminus, and then the beginning
is going to be very

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similar, and then our amino
acids are going to be

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completely different because
we're reading this in a

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different frame.

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OK, so we can see how this one
mutation, addition of one base

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pair into our DNA, has caused
us to create a completely

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different peptide.

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It's probably not going to
perform the same function.

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OK.

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So we've gone over transcription
and translation.

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You should be able at this
point to answer all of

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question two and you should
also be able to fill in

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all of table one.

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Thank you for watching.