DNA Replication

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

DNA 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