DNA is composed of nucleotides. Nucleotides are connected by phosphate bonds to form a strand. The bases on one strand form hydrogen bonds with the bases on the other to form an antiparallel, complementary double stranded molecule. The final feature of the molecular structure is that DNA assumes a helical conformation. To fit inside the nucleus, DNA must assume a very condensed structure. Therefore, chromosomal DNA is coiled around a histone protein core to form chromatin. The tight packaging of DNA in chromatin must be modified to allow DNA replication and transcription. In the process of replication, the two DNA strands separate and act as templates for the synthesis of complementary daughter strands. There are five key enzymes that work to replicate DNA, those being helicase, primase, DNA polymerase III, DNA polymerase I, and ligase. Multiple replication forks make this process of copying happen faster, which makes it possible for organisms to replicate their DNA quickly enough to grow, repair themselves, and sustain their lives.