Okazaki-fragments

Registiy of Mass Spectral Data, 412 Replication (DNA). 1106-1107 direction of, 1107 error rate during. 1107 lagging strand in, 1107 leading strand in, 1107 Okazaki fragments in, 1107 replication fork in, 1107 Replication fork (DNA), 1107 Reserpine, structure of, 65 Residue (protein), 1027 Resist, photolithography and, 505-506... 

DNAIigase Seals the single strand nick between the nascent chain and Okazaki fragments on lagging strand... 

Polymerase II (pol II) is mostly involved in proofreading and DNA repair. Polymerase I (pol I) completes chain synthesis between Okazaki fragments on the lagging strand. Eukaryotic cells have counterparts for each of these enzymes plus some additional ones. A comparison is shown in Table 36—6. 

Figure 36-16. The discontinuous poiymerization of deoxyribonucleotides on the lagging strand formation of Okazaki fragments during iagging strand DNA synthesis is illustrated. Okazaki fragments are 100-250 nt iong in eukaryotes, 1000-2000 bp in prokaryotes.

Figure 4.26 (a) DNA replication at low resolution (for example as seen by electron microscopy). Only one replication fork is visible and it appears that both strands of the parental DNA replicate continuously in the same direction, which cannot be the case, since the two strands of parental DNA are anti-parallel, (b) The problem is solved by the priming of DNA synthesis with short RNA primers, whose 3 -hydroxyl can be used by DNA polymerase, producing Okazaki fragments, while on the other strand, DNA synthesis is continuous. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)... 

The lagging strand is synthesized discontinuously as a series of small fragments (about 1,000 nucleotides long) known as Okazaki fragments. Each Okazaki fragment is initiated by the synthesis of an RNA primer by primase, and then Completed by the synthesis of DNA using DNA polymerase III. Each fr ment is made in the 5 - 3 direction. 

DNA ligase seals the nicks between Okazaki fragments, converting them to a continuous strand of DNA. 

Synthesis of DNA Leading strand Lading strand (Okazaki fragments) DNA polymerase III DNA polymerase lU DNA polymerase 6 DNA polymerase a... 

Joining of Okazaki fragments DNA ligase (requires NAD) DNA ligase (requires ATP)... 

Lagging strand synthesis, as we have noted, is accomplished in short Okazaki fragments. First, an RNA... 

The replisome promotes rapid DNA synthesis, adding -1,000 nucleotides/s to each strand (leading and lagging). Once an Okazaki fragment has been completed, its RNA primer is removed and replaced with DNA by DNA polymerase I, and the remaining nick is sealed by DNA ligase (Fig. 25-15). 

Like bacteria, eukaryotes have several types of DNA polymerases. Some have been linked to particular functions, such as the replication of mitochondrial DNA. The replication of nuclear chromosomes involves DNA polymerase a, in association with DNA polymerase S. DNA polymerase a is typically a multisubunit enzyme with similar structure and properties in all eukaryotic cells. One subunit has a primase activity, and the largest subunit (Afr -180,000) contains the polymerization activity. However, this polymerase has no proofreading 3 —>5 exonuclease activity, making it unsuitable for high-fidelity DNA replication. DNA polymerase a is believed to function only in the synthesis of short primers (containing either RNA or DNA) for Okazaki fragments on the lagging strand. These primers... 

Yet another polymerase, DNA polymerase e, replaces DNA polymerase S in some situations, such as in DNA repair. DNA polymerase e may also function at the replication fork, perhaps playing a role analogous to that of the bacterial DNA polymerase I, removing the primers of Okazaki fragments on the lagging strand. 

DNA is synthesized in the 5 —>3 direction by DNA polymerases. At the replication fork, the leading strand is synthesized continuously in the same direction as replication fork movement the lagging strand is synthesized discontinuously as Okazaki fragments, which are subsequently ligated. 

Terms in bold are defined template 950 semiconservative replication 950 replication fork 951 origin 952 Okazaki fragments 952 leading strand 952 lagging strand 952 nucleases 952 exonuclease 952 endonuclease 952 DNA polymerase I 952 primer 954 primer terminus 954... 

B. Removal of mismatched bases from the 3 end of Okazaki fragments... 

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