Mechanistically, DNA replication in eukaryotic organisms is similar in prokaryotic organisms. Before I examine their differences, I will first describe the general steps to replicate the DNA of E. coli. Scientists have gained much insight into DNA replication by studying this particular bacterium.
Unlike eukaryotes with linear chromosomes, E. coli’s chromosome is circular. DNA replication begins at a specific site called the origin of replication and continues all the way around the circular chromosome. The origin of replication in E. coli is a unique sequence of 245 base pairs. At specific binding sites along this sequence, proteins such as DnaA attach to initiate the separation of the parental strand into two template strands (Tym). This
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The most obvious reason for this complexity is the sheer size of the genomes of eukaryotic organisms. Eukaryotes have significantly more base pairs than simpler organisms like E. coli. In addition, higher organisms must replicate several chromosomes. For instance, humans have 23 pairs to replicate compared to E. coli’s one. Also, most bacteria have circular chromosomes whereas higher organisms’ are linear. The telomere ends of linear chromosomes further complicate replication as they are subject to shortening every time DNA is duplicated. Without the lengthening actions of the enzyme telomerase, the chromosome would eventually disappear. Another distinction between eukaryotic and prokaryotic organisms is the number of origins of replication required to initiate DNA replication. In human beings, multiple origins of replication are employed to replicate the entire genome in a timely manner. To ensure that each sequence is replicated only once, additional mechanisms are in place that isn’t seen in simpler organisms. Lastly, eukaryotes also employ two distinct polymerases: polymerase alpha and polymerase delta. The former is a primase and polymerase in one. The latter is similar to polymerase III of E. coli and is the more processive enzyme of the