DNA and Replication

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New strands grow at the forks

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DNA Replication

As the 2 DNA strands open at the origin, Replication Bubbles form

Prokaryotes (bacteria) have a single bubble

Eukaryotic chromosomes have MANY bubbles

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DNA Replication

Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

Single-Strand Binding Proteins attach and keep the 2 DNA strands separated and untwisted

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DNA Replication

Enzyme Topoisomerase attaches to the 2 forks of the bubble to relieve stress on the DNA molecule as it separates

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DNA Replication

Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides

Primase is the enzyme that synthesizes the RNA Primer

DNA polymerase can then add the new nucleotides

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DNA Replication

DNA polymerase can only add nucleotides to the 3’ end of the DNA

This causes the NEW strand to be built in a 5’ to 3’ direction

Direction of Replication

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Remember HOW the Carbons Are Numbered!

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Remember the Strands are Antiparallel

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Synthesis of the New DNA Strands

The Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork

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Synthesis of the New DNA Strands

The Lagging Strand is synthesized discontinuously against overall direction of replication

This strand is made in MANY short segments It is replicated from the replication fork toward the origin

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Lagging Strand Segments

Okazaki Fragments - series of short segments on the lagging strand

Must be joined together by an enzyme

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Joining of Okazaki Fragments

The enzyme Ligase joins the Okazaki fragments together to make one strand

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