DNA replication begins at the origin of replication and proceeds bidirectionally. The DNA double helix is unwound by the helicase enzyme. Single-stranded binding proteins stabilize the separated strands. RNA primers are added by the primase enzyme to provide a starting point for DNA polymerase III, which synthesizes new DNA in the 5' to 3' direction by adding nucleotides to the 3' end. The leading strand is synthesized continuously while the lagging strand requires Okazaki fragments joined by DNA ligase. Differences between prokaryotic and eukaryotic replication include prokaryotes replicating in the cytoplasm with a single origin of replication per DNA molecule, while eukaryotes replicate in the nucleus with thousands of origins

1. DNA REPLICATION
Copy and paste the following links to your web browser – watch the animation and answer the following
questions.
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wf::How Nucleotides are Added in DNA Replication
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4.swf::DNA Replication Fork
1. Where does the replication process start?
A. Stop codon
B. Origin of replication
C. Okazaki fragment
D. RNA primer
2. What enzyme unwinds the double stranded DNA helix?
DNA Helicase
3. What is the function of single stranded binding proteins?
The single strand binding protein reacts with the single stranded regions of the DNA and
stabilizes it.
4. The enzyme DNA polymerase III is a key player in replication but it has a limitation. What is it
and how is it overcome?
DNA polymerase III is the major enzyme involved in DNA replication. DNA polymerase III can
only add a nucleotide to the 3’ end of a pre-existing chain of nucleotides and it cannot initiate a
nucleotide chain.
5. Why does the enzyme primase waste time constructing an RNA primer?
A. To make the animation more colorful
B. To ensure the DNA is added in the 3’ to 5’ direction
C. So the DNA Polymerase III has a starting point
D. To help the single stranded binding proteins fold the DNA
6. What does it mean to have a complementary DNA strand?
To have a complementary DNA strand is that the nitrogen bases match up together correctly.
Adenine and thymine are corresponding and guanine and cytosine are corresponding.
7. In what direction are the nucleotides added?
A. 3’ to 5’
B. 5’ to 3’
8. What is the difference between the leading strand and the lagging strand?

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The leading strand is synthesized in the same direction as the movement of the replication fork,
and the lagging strand is synthesized in the opposite direction. The leading strand is also
synthesized continuously, but the lagging strand is synthesized in short fragments.
Why does the lagging strand require Okazaki fragments?
The lagging strand is synthesized discontinuously as a series of short segments, and these short
segments are known as Okazaki fragments.
How are Okazaki fragments on the lagging strand joined into one continuous strand?
The Okazaki fragments are processed by the replication machinery, and are stitched together,
by DNA ligase, to produce a continuous strand of DNA and a complete daughter DNA helix.
What enzyme removes the RNA on the lagging strand and replaces it with DNA?
DNA polymerase I is responsible for removing the RNA primers and replacing them with DNA.
DNA ligase then seals the gaps between the Okazaki fragments to complete the newly
synthesized lagging strand.
Look up and list at least two differences between prokaryotic replication and eukaryotic
replication.
DNA replication in Prokaryotes:
Occurs inside the cytoplasm
There is only one origin of replication per DNA molecule.
DNA replication in Eukaryotes:
Occurs inside the nucleus
Origins of replication are many (over 1000) in each eukaryotic chromosome