1. 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

2. 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

3. 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

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