Discontinuous synthesis

Leading strand = continuous synthesis. Lagging strand = discontinuous synthesis. Order of action ... 

Continuous synthesis of leading strand 5 Discontinuous synthesis of lagging strand... 

A detailed model for discontinuous synthesis could now be proposed (fig. 26.6). First, RNA primers are made on the single-strand region of the template then DNA is synthesized. Finally, the RNA is removed from the fragments, and the gaps are filled in and ligated. An understand-... 

Figure 11.3 Continuous synthesis of leading strand and discontinuous synthesis of lagging strand in the 5 —> 3 direction. Joining the fragments gives the appearance of overall growth of the lagging strand in the 3 —> 5 direction.

Figure 11.4 Discontinuous synthesis of lagging strand. Fragments are synthesized in the 5 —> 3 direction, and overall chain growth is in the 3 — 5 direction.

DNA replication is discontinuous—synthesis of one strand (called the lagging strand) lags behind the other (called the leading strand) and occurs in pieces called Okazaki fragments (Figure 24.4). Replication of the leading strand is continuous (Figure 24.3). 

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... 

Recall Describe the discontinuous synthesis of the lagging strand in DNA replication. 

Continuous versus discontinuous synthesis DNA polymerases, the enzymes... 

There is both continuous synthesis (leading strand) and discontinuous synthesis (lagging strand with Okazaki fragments)... 

Theoretically, discontinuous synthesis is not necessary for the progress of replication along the 3 ->5 replicating parent strand, but there is evidence that this may also be discontinuous. In addition to normal DNA-dependent DNA synthesis, RNA-dependent synthesis can occur in some cases (see RNA-depen-dent DNA polymerase). [A.Komberg DNA Replication, W.H.Freeman Co., 1980 A.Komberg 1982 Supplement to DNA Replication, W.H.Freeman Co., 1982]... 

Iverson, L. E., and Rose, J. K., 1981, Localized attenuation and discontinuous synthesis during vesicular stomatitis virus transcriptions. Cell 22 477. 

Okazaki fragments Nascent DNA fragments generated by discontinuous synthesis of the lagging (5 30 strand in all organisms. 

DNA polymerases function only in the 5 to 3 direction (Weiss-bach, 1977), suggesting that the discontinuous synthesis of DNA must occur on at least one strand of the DNA double helix. The discontinuous fragments (Okazaki fragments) (Okazaki and Okazaki, 1969) are joined by the action of ligases to form replicon-sized pieces, which polymerize... 

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