1. The enzyme Helicase unwinds the double helix by breaking the hydrogen bonds connencting pairs of
nitrogenous bases. This creates a Replication Fork in the DNA, a point at which the two phosphate backbones of
DNA are seperated. The replication fork splits into a Leading Strand and a Lagging Strand. The Leading Strand
is the phosphate backbone that will be built in the 5' -> 3' direction and the Lagging Strand will be built in the 3' ->
5' direction.
nitrogenous bases. This creates a Replication Fork in the DNA, a point at which the two phosphate backbones of
DNA are seperated. The replication fork splits into a Leading Strand and a Lagging Strand. The Leading Strand
is the phosphate backbone that will be built in the 5' -> 3' direction and the Lagging Strand will be built in the 3' ->
5' direction.
4. The enzyme DNA Polymerase continues from the primer in the 5' -> 3' direction, adding matching DNA
nucleotides to the original strand. These nucleotides coming in are originally nucleoside triphosphates, meaning
they have three phosphates connected to them. As with ATP, the bonds between the phosphates carry large
amounts of energy which is used to power DNA Polymerase.
5. On the leading strand, DNA Polymerase works continuously. However, because the lagging strand runs in the
opposite direction, DNA Polymerase works in segments on the lagging strand. These segments are called
Okazaki fragments.
6. DNA ligase connects the Okazaki fragments to the growing strand of DNA and the process is complete.
nucleotides to the original strand. These nucleotides coming in are originally nucleoside triphosphates, meaning
they have three phosphates connected to them. As with ATP, the bonds between the phosphates carry large
amounts of energy which is used to power DNA Polymerase.
5. On the leading strand, DNA Polymerase works continuously. However, because the lagging strand runs in the
opposite direction, DNA Polymerase works in segments on the lagging strand. These segments are called
Okazaki fragments.
6. DNA ligase connects the Okazaki fragments to the growing strand of DNA and the process is complete.
Want to Review?
Watch either Mr. Roisen himself explain the process (on the Left) or watch this helpful animation of DNA Replication in action
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