13-3: DNA Replication

-the process by which DNA makes a copy of itself
-occurs during interphase, prior to cell division

DNA replication

Steps of DNA replication

1. DNA helicase (enzyme) unwinds the DNA. The junction is called a replication fork.
2. DNA polymerase adds the complementary nucleotides and binds the sugars and phosphates. DNA polymerase travels from the 3' to the 5' end.  The DNA is called the template strand.
3. DNA polymerase adds complementary nucleotides on the other side of the ladder. Traveling in the opposite direction.
4. One side is the leading strand - it follows the helicase as it unwinds.
5. The other side is the lagging strand - its moving away from the helicase (in the 5' to 3' direction).

Replication is called semi-conservative, because one half of the original strand is always saved, or "conserved"

Problem: it reaches the replication fork, but the helicase is moving in the opposite direction. It stops, and another polymerase binds farther down the chain.

This process creates several fragments, called Okazaki Fragments, that are bound together by DNA ligase.

6. During replication, there are many points along the DNA that are synthesized at the same time (multiple replication forks). It would take forever to go from one end to the other, it is more efficient to open up several points at one time.


Replication Errors – can cause a genetic MUTATION
-- PROOFREADING by the polymerase prevents mismatches
-- DNA REPAIR ENZYMES can repair damaged DNA also

Additional Resources

Animation of Replication (stolaf.edu)
Animations of Replication (mcgraw-hill)

Replication Tutorial (wiley.com)
Replication Fork (mcb.harvard.edu)