8.2 and 8.3 - DNA Structure and Replication (Part 2)

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Lesson Objectives: Explain the process of DNA replication and the role of the major proteins involved.
Step 1: Helicase
Step 2: Single-Stranded Binding Proteins
Helicase unzips the double helix by
breaking the hydrogen bonds
between the nitrogenous bases.
• To make sure that the separated DNA
strands stay apart, single-stranded
binding proteins bind to each strand
of DNA.
•
Alia Kanan, 2019
Step 3: Primase
•
DNA Polymerase adds/synthesizes free-floating nucleotides to form
hydrogen bonds with the template strand
Step 4: Primase DNA Polymerase
•
•
DNA Polymerase adds/synthesizes free-floating nucleotides to form hydrogen bonds with
the template strand in the 5’ to 3’ direction of the new strand.
DNA polymerase enzymes bond the nuclotides together to form the double helix.
Step 5: Ligase
• Nucleotides are added in
the 5’ to 3’ direction of the
NEW strand.
• The leading stand is
continuous while the
lagging strand is
discontinuous and produces
small Okazaki fragments.
• Ligase “glues” the fragments
together.
DNA Replication Step-by-Step
Proof-reading
•
DNA polymerase can find and correct errors as replication is proceeding.
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