After Watson and Crick proposed their model for
the structure of DNA, scientists focused attention
on how this molecule replicates. Replication is
an essential function of the genetic material and must be
executed precisely if genetic continuity is to be maintained
following cell division. This is an enormous and complex
task. Consider for a moment that in the human genome,
about 3 billion base pairs exist within the 23
chromosomes. To duplicate a molecule of this size faithfully
requires a mechanism of extreme precision. Even an
error rate of only one in a million will still create
3000 errors, obviously an excessive number during each
replication cycle. While it is not error-free, an extremely
accurate system of DNA replication has evolved in all
organisms.
As Watson and Crick wrote in their 1953 paper, the
model of the double helix provided their initial insight
into how replication could occur. This mode, called semiconservative
replication, is strongly supported from
numerous studies of viruses, prokaryotes, and eukaryotes.
Once the general mode of replication was clarified,
research to determine the precise details of DNA synthesis
intensified. What has since been discovered is that
numerous enzymes and other proteins are necessary to
copy a DNA helix. Because of the complexity of the
chemical events during synthesis, this subject remains an
extremely active area of research.
In this chapter we discuss the general mode of replication
as well as the specific details of the synthesis of DNA. The
research leading to this knowledge is yet another link in our
understanding of life processes at the molecular level.
- 11.1 DNA Is Reproduced by Semiconservative
Replication
- The Meselson–Stahl Experiment
- Semiconservative Replication in Eukaryotes
- Origins, Forks, and Units of Replication
- 11.2 DNA Synthesis in Bacteria Involves Three
Polymerases, as well as Other Enzymes
- DNA Polymerase I
- Synthesis of Biologically Active DNA
- DNA Polymerase II and III
- 11.3 Many Complex Issues Must Be Resolved During
DNA Replication
- Unwinding the DNA Helix
- Initiation of DNA Synthesis
- Continuous and Discontinuous DNA Synthesis
- Concurrent Synthesis on the Leading and Lagging
Strands
- Proofreading and Error Correction During DNA
Replication
- 11.4 A Coherent Model Summarizes DNA Replication
- 11.5 Replication Is Controlled by a Variety of Genes
- 11.6 Eukaryotic DNA Synthesis Is Similar to, but More
Complex than, Synthesis in Prokaryotes
- Multiple Replication Origins
- Eukaryotic DNA Polymerases
- 11.7 The Ends of Linear Chromosomes Are
Problematic During Replication
- 11.8 DNA Recombination, Like DNA Replication, Is
Directed by Specific Enzymes
