It is said that information is king. But
information not only needs to be transmitted
but also replicated. That's
certainly important for
what happens in the cell with respect to
its nucleic acid information.
In this lecture, I am going to cover the
replication of DNA and the repair of DNA.
So DNA replication is a process that is essential
for the transmission of genetic information.
The structure of DNA discovered in 1953
gave clues to how it will be replicated.
First of all, this DNA molecule is complimentary.
These bases on one strand form compliments
to bases on the other strand.
There is phosphodiester backbone that holds the
individual bases together on one strand, as we can see.
And the bases project into the
middle of what is the double helix.
Now the base pairing occurring in the center is
stabilized by hydrogen bonds, as we will see.
So, as we will see, there are some significant
differences between the systems of replication
that involved in prokaryotic versus eukaryotic cells;
because, of the nature of the
genetic information in the two.
But the overall DNA replication process itself,
mechanistically, is not significantly different.
Now when we think about DNA replication,
at the very beginning of DNA replication
it starts at a specific sequence.
We have seen in another lecture how
transcription of RNA begins at a promoter.
In DNA replication, the replication process
begins at a sequence called an origin.
Proteins bind to the origin to help the replication process
to occur very much like what we saw in transcription
except for here the idea is the replication of DNA.
They will open the double helix to allow the access
of the replication proteins to get in and begin.
The replication requires a "reader" of the template
and a catalytic function to make phosphodiester bonds.
Basically what I am talking about
here is a DNA polymerase.
It reads one strand, grabs the appropriate base, and then
incorporates that into the strands that it is building.
Now there are several proteins involved in the
replication of DNA and I'd like to just first list them
and then we will see individually what they do later.
First, there is the DNA polymerase that's
involved, as I said, in actually making
the phosphodiester bonds to join everything.
There is a primase that's a protein that actually
helps to start the synthesis of the DNA.
There is something called the single stranded binding protein
which as its name suggests, binds to single strands.
Enzymes called helicases help the process to
advance, as we shall see, at an incredible rate.
An enzyme called topoisomerase helps with traffic
jam that happen during the replication process.
On these traffic jams, literally, can be knots
in the DNA if they are not taken care off.
A primer remover is necessary; because, the primer
is where the replication process gets started
and, as we will see, that primer start is not DNA.
In last in the process we have to have something called
DNA ligase; because, this is how all the individual pieces
of the DNA during replication get joined together.