DNA Replication

DNA structural and organization

DNA molecules are wrapped tightly around histone proteins to form structures called nucleosomes. Nucleosomes are linked together by DNA strands and stacked on top of each other to form chromatin. Chromatin is further coiled into thicker structures called chromosomes.

Semi-conservative

Model of DNA replication that means that each new DNA molecule is made up of one parents strand and another replicated strand.

DNA replication steps

Initiation, elongation, and termination

True or false: DNA replications before cell division begins

True

Initiation

DNA’s double helix unwinds. Helicase binds to the origin of replication and create two replication forks. Leading strand has nucleotides organized 3’-5’ and lagging strand is organized 5’-3’. RNA primases attach RNA primers to each strand at the start.

Elongation

After the primers are added, DNA Polymerase III adds nucleotides to the 3’ end of the new strand. DNA Pol. only moves in the 5’-3’ direction. Perfect for leading strand, not good for lagging strand. Okazaki fragments must be added by DNA polymerase. This creates multiple 3’ ends for nucleotides to bind to.

True or false: new DNA strands are complementary to the parent strand

True

Termination

DNA Polymerase I removes the RNA primers on both leading and lagging strands. The primers are replaced with DNA and an enzyme called ligase seals the backbone of both strands and Okazaki fragments with phosphodiester bond. Replicated strands unwind into a double helix with parent strand.