DNA replication - 3D

DNA is a double helix made of two strands, each composed of four chemical bases: A, C, G, and T. These strands are complementary, with A pairing with T and C with G. Each strand has a 5' and 3' end, and the two strands run in opposite directions.

The first step in DNA replication is the separation of the two DNA strands by the enzyme helicase, forming a replication fork. Each separated strand then serves as a template for synthesizing a new strand.

Primase creates an RNA primer, marking the starting point for the new DNA strand. DNA polymerase then binds to the primer and adds DNA bases in the 5' to 3' direction. The leading strand is synthesized continuously in this manner.

The lagging strand, running in the opposite direction, is synthesized in small fragments called Okazaki fragments. Each fragment begins with an RNA primer, and DNA polymerase adds bases in the 5' to 3' direction. The process repeats as new primers are added further down the strand.

After new DNA is made, exonuclease removes all RNA primers. Another DNA polymerase fills in the gaps with DNA, and finally, DNA ligase seals the DNA fragments, creating continuous double strands. DNA replication is semi-conservative, meaning each new DNA molecule consists of one old and one new strand.