These are regions of the DNA molecule that are recognized by special origin recognition proteins that bind the DNA. In either situation, DNA replication is initiated at sites called origins of replication. Figure 5.1.1: Semi-conservative DNA replication coli, there is a single circular chromosome. In cells like our own, the vast amount of DNA is broken up into many chromosomes, each of which is composed of a linear strand of DNA. Cells, whether bacterial or eukaryotic, have to replicate all of their DNA before they can divide. Even in bacteria, the number is in the millions. The sheer number of nucleotides to be copied is enormous.įor example, in human cells, the number of nucleotides to be copied is on the order of several billion. Although the specific proteins involved are different in bacteria and eukaryotes, it is useful to understand the basic considerations that are relevant in all cells, before attempting to address the details of each system.Ī generalized account of the steps in DNA replication is presented below, focused on the challenges mentioned above. Numerous proteins involved in replication have been identified and characterized, including multiple different DNA polymerases in both prokaryotes and eukaryotes. These investigations have revealed that DNA replication is carried out by the action of a large number of proteins that act together as a complex protein machine called the replisome. Our understanding of the process of DNA replication is derived from studies using bacteria, yeast, and other systems, such as Xenopus eggs. With this in mind, we can begin to examine how cells deal with each of these challenges.
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