Lecture Outline for March 4, 2005


Topic: DNA replication

Chapter 12 section 12.3

Figures used in lecture: 12.10, 12.12

Additional resources

DNA Replication

DNA Replication (again)


Models of DNA Replication

three models were proposed:

1. conservative

2. semiconservative

3. dispersive


Experiment of Meselson and Stahl, 1957

  1. grow bacteria in medium containing 15N; all the DNA now contains 15N-labeled DNA
  2. transfer bacteria to 14N medium
  3. isolate DNA
  4. perform CsCl centrifugation to separate DNA based on density\
  5. result: all DNA was of intermediate density (14N-15N hybrids)
  6. allow bacteria to replicate
  7. isolate DNA
  8. perform CsCl centrifugation to separate DNA based on density

result: DNA is 14N-15N hybrid, DNA is 14N-14N light density

This experiment indicates that the semiconservative model of DNA replication is correct.


DNA Replication

Define/explain: origin of replication (ORI), parental strands of DNA, daughter strands of DNA, Okazaki fragments

DNA replication involves many enzymes including helicase, primase, DNA polymerase, DNA ligase

You should be able to

1. Explain each of the proposed models for DNA replication being able to propose the results of the Meselson & Stahl experiment for DNA that is replicating either by a conservative method or a dispersive method.

2. List and explain the steps of DNA replication

3. List the enzymes and their function