DNA replication in eukaryotes

The multiple sites that serve as origins for DNA replication in eukaryotes are poorly defined except in a few animal viruses and in yeast. However, it is clear that initiation is regulated both spatially and temporaUy, since clusters of adjacent sites initiate rephcation synchronously. There are suggestions that functional domains of chromatin replicate as intact units, implying that the origins of rephcation are specificaUy located with respect to transcription units. 

DePamphilis, M. L., ed. (1996) DNA Replication in Eukaryotic Cells, Cold Spring Harbor Lab. Press, Cold Spring Harbor, New York... 

Replication of the Escherichia coli Chromosome Initiation and Termination of Escherichia coli Chromosomal Replication DNA Replication in Eukaryotic Cells Eukaryotic Chromosomal DNA SV40 Is Similar to Its Host in Its Mode of Replication... 

Related topics DNA replication in bacteria (F3) Transcription in DNA replication in eukaryotes (F4) prokaryotes (G2) RNA structure (Gl) Transcription in eukaryotes an overview (G5)... 

The control of DNA replication in eukaryotes is more complex than in bacteria. Once a cell enters S phase, the multitude of individual replicons throughout the genome probably replicate in a defined order. It is known that, in some situations, the duration of S phase can vary greatly. 

Sharova, N.P., and E.B. Abramova. Initiation of DNA replication in eukaryotes is an intriguing cascade of protein interactions. Biochemistry 2002 67 1217-1223. 

Initiation of DNA replication in eukaryotes appears to be more complex than what has been found in bacteria. 

DNA replication in eukaryotes is more complex. The human genome consists of approximately three billion nucleotide pairs. Just one chromosome may be nearly one hundred times longer than a bacterial chromosome. To accomplish this huge job, DNA replication begins at many replication origins and proceeds bidirectionally along each chromosome. 

Higher Order Chromatin Structure in the Nucleus (Figure 28.12, Figure 28.13) The Cell Cycle and DNA Replication in Eukaryotes... 

The general features of DNA replication in eukaryotes are similar to those in prokaryotes. Table 10.5 summarizes the differences. As with prokaryotes, DNA replication in eukaryotes is semiconservative. There is a leading strand with continuous synthesis in the 5 3 direction and a lagging strand with discontinuous synthesis in the 5 3 direction. An RNA primer is formed hy a specihc enzyme in eukaryotic DNA replication, as is the case with prokaryotes, hut in this case the primase activity is associated with Pol a. The structures... 

Another important difference between DNA replication in prokaryotes and in eukaryotes is that prokaryotic DNA is not complexed to histones, as is eukaryotic DNA. Histone biosynthesis occurs at the same time and at the same rate as DNA biosynthesis. In eukaryotic replication, histones are associated with DNA as it is formed. An important aspect of DNA replication in eukaryotes, specifically affecting humans, is described in the Biochemical Connections box on pages 282 and 283. 

Recall How does DNA replication in eukaryotes differ from the process in prokaryotes ... 

It is faster in prokaryotes. The DNA is smaller, and the lack of compartmen-talization within the cell facilitates the process. DNA replication in eukaryotes is linked to the cell cycle, and prokaryotic cells proliferate more quickly than those of eukaryotes. 

DNA replication in eukaryotes is fundamentally similar to that in prokaryotes. It is catalyzed by DNA polymerases which synthesize new DNA strands in a 5 —>3 direction. Synthesis of leading strand eukaryotic DNA is continuous while synthesis of lagging strand DNA entails the production of Okazaki fragments. However, there are a number of differences between prokaryotic and eukaryotic DNA replication. 

Termination and telomere The binding of the replication termination protein (Tus protein) to the terminus region (x locus) in prokaryotic chromosome impedes the progression of the replication fork and terminates DNA replication. In eukaryotes, the linear chromosomes terminate with telomeres by the action of telomerase. 

Table 64.1 DNA replication in eukaryotes. Numbers refer to Figure 64.1 opposite.

Table 71.1 Summary and comparison of DNA replication in eukaryotes and prokaryotes (see Chapters 63 and 64). Numbers refer to Fig. 64.1.

The replication process must occur at extremely high speed, since E. coli can divide every 20 minutes under optimal conditions. This requires the replication of at least 133,000 base pairs (133 kbases) or 50 un DNA per min. DNA replication in eukaryotes occurs much more slowly. The process is catalyst by DNA polymerase (EC 2.7.7.7) which joins the four 5 -nu-cleoside triphosphates into the linear DNA molecule, using a sin e-stranded DNA as a template. Each nucleotide loses a pyrophosphate group (PPj), and the energy stored in these bonds drives the reaction. 

DNA replication in eukaryotic cells is fundamentally the same as that in bacteria. Replication is semi-conservative, occurs in a 5 3 direction, and requires a template, a primer and deoxy-... 

Tdomerase is an enzyme that helps to maintain chromosome length during DNA replication in eukaryotes by producing the telomer TTAGGG. This enzyme has a key role in the development of cancers. 

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