Now that you have a great
understanding of transcription,
it’s time to come on and look
at the details of translation.
Now we’re moving from messenger
RNA to the polypeptide itself.
And we’re switching languages.
So we’re taking the ingredients
on our printed copy
and we’re making our final
dish, the polypeptide.
So by the end of this lecture,
you will be able to explain
the tRNA charging process as well
as diagram ribosomal anatomy
and describe what happens during the initiation,
elongation, and termination phases.
We will also be able to distinguish the
difference in bound and free ribosomes
during translation process.
So let’s get started.
Looking at tRNAs.
There are a lot of different ways for
us to depict a translational RNA.
Most of the time, we will
end up using the icon
on the right hand side
to represent tRNA.
Either way, all of our tRNAs will
have an amino acid accepting end
as well as an anticodon end,
which is on the loop of RNA
and will pair with the
codons on messenger RNA.
So now that we have an understanding
of the basic anatomy of a tRNA,
let’s look at how we
get them charged.
That is how do we get them associated
with the appropriate amino acids
so that they can go to the
ribosome and do their job.
So here, we have an
that is my favorite
enzyme to say.
And it has a binding
site for the tRNA.
Now, each tRNA will have a specific binding
site on a specific tRNA synthetase.
And it will have an amino acid binding
site that’s specific to the amino acid
that needs to matched
to that tRNA.
It requires a little bit
of energy to charge it.
And so we apply some ATP, which is cleaved,
leaving AMP behind and will take a tRNA
that’s specific to that tRNA synthetase
and put it into
the binding site.
The anticodon on that tRNA
will pair with tRNA codons
essentially inside the tRNA synthetase,
that’s how they recognize each other
and then we’ll pair the
amino acid with the tRNA.
We lose the AMP and then
we can release the tRNA
that is now charged, has
its specific amino acid.
It’s ready to go to the ribosome
and do its duties there.
So now we know how we charged
our tRNA synthetases.
It’s important to recognize that there
are multiple different tRNA synthetases,
and that it varies how many there
are from species to species.
We should have at least 20 of them because
there are 20 different amino acids
and we need to bind to
specific amino acid to a tRNA.
But as we’ll see later,
we can have a little bit of wobble
in the pairing of the anticodon.
You’ll recall when we learned
about the genetic code,
there are some codons or some amino acids
in which there are several different ways
to code for them
on messenger RNA.
So we’ll look at that towards
the end of this lecture.