How does DNA polymerase work

DNA replication

DNA replication process

In this article we explain the exact process of DNA replication. For everyone who would like to repeat the topic of DNA, you will find the right article here!

For an introduction to the subject of DNA replication, watch the learning video from our partner “Die Merkhilfe”!


Human body cells contain a total of 46 chromosomes. One speaks here of a double set of chromosomes (diploid, 2n), since the chromosomes are present as homologous pairs. This means that two chromosomes code for the same information, for example hair color. One of these homologous chromosomes is obtained from the father during fertilization, and one from the mother. It is therefore possible that you get the information for brown hair from the father, but the information for blonde hair from the mother - this results in different variations of characteristics for each person. The body cells of a single person do not differ from one another in their genetic information.

In order for a cell to divide, all components of the cell have to be doubled in the course of the cell cycle. The DNA must also be copied identically. This process is known as replication. Many different enzymes are involved here, and they perform different tasks.

First, the enzyme helicase untwists the double helix, creating an open replication fork. Thereafter, enzymes called primase bind to both strands of the DNA. These add small RNA segments, the primers, to the strands as attachment points. This is where the DNA polymerase can start, which now links free nucleotides complementary to the existing DNA strand.

Both DNA and RNA polymerases can only connect nucleotides by connecting the phosphate (at the 5'-end) of a free nucleotide to the 3'-end of a solid nucleotide. The new strands are therefore always extended at the 3'-end. Since both “original strands” of DNA run complementary to one another, the replication on both strands differs from one another. The newly synthesized DNA matrices are therefore referred to as the leading strand and the secondary strand


The leading strand is the strand of DNA that can be continuously synthesized. Here the primase only needs to set a single primer on which the DNA polymerase can begin to synthesize. The leading strand is synthesized from the 5'- in the 3'-direction, the complementary "original strand" is therefore read from the 3'- in the 5'-direction.

The following strand, on the other hand, has to be synthesized discontinuously. Here the primase places many primers at smaller intervals so that the DNA polymerase always has new starting points to synthesize small sections of the following strand. These smaller stretches of RNA primers and smaller stretches of DNA are called Okazaki fragments. In the end, another enzyme is used: the ligase. This replaces the RNA primers with DNA and links the small fragments with one another, so that a complete, new DNA strand is created.