DNA Replication Helicase DNA Polymerase DNA Ligase The process where cells duplicate/copy their DNA for division Fast process, occurs at about 50 nucleotides per second! Driven by enzymes Helicase DNA Polymerase DNA Ligase Occurs at many different origins on the same DNA strand at one time Produces identical DNA molecules

DNA Replication – Steps Helicase enzyme unzips DNA strand at an “origin” causing a replication fork to form Another enzyme, DNA polymerase, attaches after helicase opens the double helix DNA polymerase reads in the 3’ to 5’ direction DNA polymerase adds complementary bases to the template strand DNA polymerase falls off, leaving 2 identical DNA molecules Helicase

DNA Replication Since DNA Polymerase only reads in 1 direction (3’ to 5’), 2 methods are required to replicate DNA: Leading Strand – this strand is created continuously since the 3’ end is read first Lagging Strand – this strand is created in small fragments called Okazaki fragments, because this strand runs 5’ to 3’ The lagging strand replicates DNA in segments, so DNA Ligase will link these segments together to make 1 DNA strand

DNA Replication Errors can occur during replication (ex: A-C. T-G, etc…) Gene mutations can occur (ex: substitution, deletion, etc..) Overview: