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Hello and welcome to this video tutorial
we are going to discuss transcription and translation problems
in particular in this tutorial
we will consider the case where you were given the template strand
sequence and you were asked to determine what the resulting
mRNA would be assuming the template strand was transcribed
and what the resulting peptide would be
assuming that the mRNA was translated
now we're going to make some simplifying assumptions
one of which is we do not require a start code on which
is not how it happens in cells but to make these problems
feasible that will be one of our assumptions and also we're going to
assume that if we
encounter is stop code on that translation will stop at that point
and we would just enter the amino acid sequences
Inc included up to that point so to begin
we're gonna imagine that we're given the sequence G
whoops G
T A C
G A we're told
that this is the template strand so many right that
just to remind ourselves that that
now one convention you need to be aware I've
is that if you're given a single-stranded DNA
that it is assumed to be
in the five prime to three prime direction
so unless you're told otherwise you should assume
that the sequence reads in five by prime to three prime direction
so we need to think about what the resulting
sequence the mRNA would be now
remember that are in a
is transcribed
in the five prime to three prime direction so we're actually
reading the template three prime to five prime
so that synthesis at the mRNA can proceed
five prime to three prime as it must so
opposite the a we would have a U
since its mRNA and not a T which we would find in DNA
opposite the G we're going to have to C
opposite the C we're going to have the G
we're just adding the complementary bases
opposite the A we would have another U
opposite the T we would have a an A
and then opposite the G we would have a C
so that is the sequence of are
mRNA now what I like to do just to keep things straight
is I wanna flip this around
and write this five prime to three prime
so I'm gonna write U C
G U
A C just
remind myself that this is still the mRNA but now I've written five prime to three
prime end
I'll explain why on the next screen continuing on
i'd just written or rewritten our mRNA
in the five prime to three prime direction which is where we left off
on the previous screen now the reason why we we flip that
so that it read or reads five prime to three prime
is because translation
in the sale proceeds in the five prime to three prime enter the mRNA is read
five Prime to three prime so again because we're not assuming we needed to start code
codon
we're just going to take the first three bases and that'll be our first codon
so U C G if you look that up in your genetic code you would see that that
encodes
for the amino acid
Serine which the one letter code for Serine is a capital S
and then
the next three U A C
this code on encodes for the amino acid
tyrosine and the one letter code for the amino acid
tyrosine is seen as a capital Y so are resulting
peptide which would be a dipeptide would simply be
capital S capital Y if we're told to give the answer using the one letter
code
or Ser
capital S lower case e r for Serine using the three-letter code
and in capital T y r for tyrosine using the three-letter
in general the questions on this tutorial or gonna ask you
for the sequence the resulting peptide using the one letter to
so that concludes this video tutorial
for the case where you start out having been given a template strand
in another video tutorial we will treat the case
were you start out and you're given the coatings strand