Okazaki fragment에 RNA primer가 필요한 이유.
DNA replication begins with a partial unwinding of the double helix at an area known as the replication fork. This unwinding is accomplished by an enzyme known as DNA helicase. This unwound section appears under electron microscopes as a “bubble” and is thus known as a replication bubble.
As the two DNA strands separate (“unzip”) and the bases are exposed, the enzyme DNA polymerase moves into position at the point where synthesis will begin.
The start point for DNA polymerase is a short segment of RNA known as an RNA primer. The very term “primer” is indicative of its role which is to “prime” or start DNA synthesis at certain points. The primer is “laid down” complementary to the DNA template by an enzyme known as RNA polymerase or Primase.
Because the original DNA strands are complementary and run anti-parallel, only one new strand can begin at the 3′ end of the template DNA and grow continuously as the point of replication (the replication fork) moves along the template DNA. The other strand must grow in the opposite direction because it is complementary, not identical to the template strand. The result of this side’s discontiguous replication is the production of a series of short sections of new DNA called Okazaki fragments (Okazaki는 DNA의 조각들을 발견하고 연구한 일본 과학자의 이름). To make sure that this new strand of short segments is made into a continuous strand, the sections are joined by the action of an enzyme called DNA ligase which LIGATES the pieces together by forming the missing phosphodiester bonds.
The last step is for an enzyme to come along and remove the existing RNA primers and then fill in the gaps with DNA. This is the job of yet another type of DNA polymerase which has the ability to chew up the primers (dismantle them) and replace them with the deoxynucleotides that make up DNA. Here is a link with a diagram of the overall process of DNA replication of Okazaki Fragments.