In prokaryotes, DNA replication or DNA synthesis begins at the origin of chromosomal replication or the REC. This is a specific sequence found on the DNA molecule. It's about 250 bases and it's recognized by a bunch of different initiation proteins. One of those proteins is DNA A, and that's the first molecule that will bind to this complex and start to open up the two strands, exposing them to the machinery. The DNA helix, that double helix, will be unwound by DNA B helicase.
DNA B helicase is an ATP-dependent enzyme, which means it's going to use ATP. and it will get helped onto that DNA molecule by a loader protein called DNA-C. So DNA-C loads up DNA-B to the DNA molecule and there will be two of these that will get loaded up. So we'll have two of these molecules, one onto each strand.
And this complex is sometimes known as the prime ozone. So you'll see that phrase too. Now DNAB helicase is going to start to spin using ATP and as it spins it's going to start to break the hydrogen bonds that are holding together these nucleotides.
So it will start to spin and as it does so it's going to break apart those nucleotides. As it does so it's going to move in this direction which is called the replication form. and we'll come back to that in a moment. But as it does so, it leaves behind the two strands. Now, these bases are complementary, and there's nothing stopping them reforming their hydrogen bonds.
So single-stranded binding proteins are placed onto the lagging strand of our DNA replication fork, and that prevents them from reforming these bonds. So these bonds are unable to reform these hydrogen bonds, and Ahead of this as well, we also should mention our topoisomerase 2 here, DNA gyrase. That DNA gyrase is breaking the DNA molecule ahead of the replication complex. And as it's doing so, it's relieving the tension here that's being generated on this molecule.