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DNA Replication – What and Why
Replication = DNA making copies of itself– DNA must be copied before a cell can divide– Each new cell will have
a complete set of DNA
History of Replication
• Watson & Crick – realized that complementary base pairing provided a way for DNA to copy itself - base pairing could allow a new strand to be built on an old strand
DNA Replication
• In most prokaryotes, DNA replication begins at a single point and continues in two directions.
• In eukaryotic chromosomes,– DNA replication occurs at hundreds of places.– Replication proceeds in both directions until each
chromosome is completely copied.
Critical Thinking Check
• How does the structure of a eukaryote and a prokaryote relate to the manner in which the DNA is replicated in each?
DNA Replication: Process
• Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles
DNA Replication: Process
• The nitrogen bases on the original DNA strands are exposed in the replication bubbles.
• They serve as a template to build new DNA strands
DNA Replication
• The ends of the replication bubbles known as the replication fork is where replication begins
DNA Replication – DNA Polymerase
• The enzyme DNA polymerase brings new nucleotides to the replication fork - it pairs them according to base
pairing rules A pairs with T C pairs with G
DNA Replication
• The process continues until 2 complete copies of the DNA are produced
• Each copy of the DNA contains one strand of DNA
from the original DNA molecule and one new strand that was produced by replication
• Known as semi-conservative replication
Knowledge Check
• Summarize the major events that occur in DNA replication (you should come up with at least 3 unique steps).
Summary of DNA Replication
1. Hydrogen bonds between base pairs are broken
2. DNA unwinds – replication bubbles form3. Free nucleotides pair up with their respective
bases4. DNA polymerase proofreads each new strand
of DNA5. Two double helices are now present