So now, we have the
initiation and elongation.
And termination, we don’t understand
very well in eukaryotes yet.
We have also to make some modifications
to the messenger RNA transcript
in order to make it suitable
to leave the nucleus.
So we’re going to add a
5’ cap, a poly-A tail
to protect it out in the
world of the cytosol
and we’re also going to cut out
sections that don’t code for anything.
So first, we bind
the 5’ GTP cap.
I think about the cap protecting it.
The cap, he puts the cap on.
Let’s say methylated cap.
So it’s a methyl group on there.
And the cap is actually
put on backwards.
It’s a nucleotide because it’s a GTP
but some reason, this methylated cap
will bind to the 5’ phosphate
group with its 5’ phosphate group.
So it’s a cap that’s on backwards.
He's a pretty cool mRNA.
And he needs that on before he can go
out into the real word of the cytosol.
The other thing that will happen
is we will add a poly-A tail.
So poly-A tail is actually added by
poly-A polymerase, a separate polymerase,
who comes along and sort
of cuts off the first tail
and then polymerize the addition
of all these poly-A tails.
I imagine the poly-A tail as a
another means of protection.
So when the mRNA goes out and swims through
the cytosol, it doesn’t really but –
It’s protecting him from all these
other enzymes and PAC-MAN things
that are running around in the
cytosol trying to chomp at his tail.
So he’s protected with 5’
cap and a poly-A tail.
He’s good to go.