Three possible models for semiconservative replication of DNA.

Test of models using Tritiated [3H] thymidine

Origin	Growing Regions	Structure	Results
Two	Two	Ends	No
One	One	Forks	Very Rare
One	Two	Forks	Common

Now let us look at a model to explain the rest of the data.

The replication bubble in Drosophila embryos

The system is very similar in E. coli

Bidirectional replication of circular molecules give rise to theta structures.

General Scheme for DNA replication

• Initiation - Start of macromolecular syntheses (N - (N-1) ) -

  • Starts with a bubble and RNA Primers

  • RNA Primers are removed by pol1

  • DNA pieces are ligated together

  • Flash Summary

• Elongation - step by step addition of Nucleotides (N-2)

  • RNA Primers are removed by pol1

  • DNA pieces are ligated together

  • Flash Summary

• Termination - stop of replication (N - (N-1) )

  • What happens at the "End"?

In vitro Enzymatic Replication of DNA

Chemistry of Chain elongation reaction catalyzed by DNA Polymerase.

Model for bidirectional migration of two forks

Origin of Replication - OriC

Origins of replication in E. coli

Autonomous Replicating Sequences in Yeast

Initiation of Replication

Model from text

 What does it mean to prime the pump?  

      Primase starts the synthesis of DNA

Both strands are both Leading and Lagging

The structure of the growing forks

Ligase hooks things together

How can the polymerase go both directions at once ?

Again, how can the polymerase go both directions at once?

A second model from text part a, part b, and summary

Text iGenetics by Peter J. Russell

This web site is provided for instruction in Botany and Zoology 342

by Kenneth G. Wilson,
Professor of Botany
Miami University
wilsonkg@muohio.edu