Replication bubble

Formation of replication bubbles with ligation of the newly synthesized DNA segments. 

Figure 36-17. The generation of "replication bubbles" during the process of DNA synthesis. The bidirectional replication and the proposed positions of unwinding proteins at the replication forks are depicted.

DNA replication occurs at several sites—called replication bubbles—in each chromosome. The entire process takes about 9 hours in a typical cell. 

The base sequence at the origin of replication is recognized and bound by the dna A protein. The two parental strands of DNA are pulled apart to form a replication bubble. ... 

Replication starts at a single origin, is bi-directional and semi-conservative. Each replication bubble (or eye) consists of two replication forks. 

Yes, both are actively involved in DNA replication and move at approximately equal rates in opposite directions around the circular molecule. This is known as bidirectional replication. The replicated portion of the molecule is referred to as a replication bubble or eye form (because of its appearance in diagrams). The size of the bubble varies from being extremely small up to nearly twice the size of the nonreplicating chromosome. Obviously, the site on the circular molecule of a very small bubble represents the region within which replication was initiated. 

Fig. 16-5 Tandemly arranged replicons in eukaryotic DNA generate a chain of replication bubbles. O denotes an origin of replication.

A replicating bacterial chromosome exists as a so-called 9 structure (because of its appearance in electron micrographs and diagrammatically), in which the upper closed section represents the duplicated portion, or replication bubble. Why is there now an origin of replication situated at the middle of each arm of the bubble ... 

A multiforked bacterial chromosome is one that contains more than two replication forks and results from reinitiation at the daughter origins within a replication bubble. In this situation, cycles of replication are completed at more frequent intervals, and this gives shorter generation times. It occurs under conditions of fast growth, induced by nutritionally rich media. 

Devise a possible sequence of protein- (enzyme)-mediated events for the generation of a replication bubble at an origin of replication in double-helical DNA. 

Priming and synthesis of lagging strands. Generation of replication bubble. 

DNA polymerase activity and 3 —> 5 direction exonuclease activity. Because there are 2 strands to be replicated the 2 strands of the dsDNA have to unwind and in a circular dsDNA bidirectional replication results in a replication bubble bounded by two Y-shaped replication forks that move around the circle. The continuous or leading strand is made unbroken around its ssDNA template. However the other (antiparallel) strand (the lagging strand), proceeding from the same starting point as the dsDNA opens up, is made with the same 5 3 ... 

Origin of DNA replication. The physical location in a chromosome or genome where DNA replication is initiated by the formation of a replication bubble. 

Fig. 21-8 Replication of DNA double helix, (a) DNA synthesis at a pair of replication forks with expansion of the replication bubble. DNA chains are not shown in helical form, (ft) Complementary chains are synthesized via base pairing. (After J. McMurry and M. E. Castellion, Fundamentals of General, Organic, and Biological Chemistry, Prentice-Hall, Englewood Cliffs, NJ, 1992.) (c) Semiconservative replication. (After J. D. DeLeo, Fundamentals of Chemistry General, Organic, and Biological, Scott, Foresman, Glenview, IL, 1988.)...

Problem 21.45. Why does DNA replication involve simultaneous synthesis at many replication bubbles ... 

Eukaryotes tend to have much more DNAthan prokaryotes. Therefore, to speed the process of replication it occnrs in multiple replication bubbles (Fig. 63.3). Within each bubble, DNA replication occnrs at two replication forks. However, in prokaryotes there is only a single replication bubble (Fig. 63.4). In both prokaryotes and enkaryotes, the consensus sequence at an origin of replication varies but all have a high content of A and T, which facilitates separation of the strands. Remember that A=T bonds (two hydrogen bonds) are more easily separated than CsG bonds (three hydrogen bonds). 

Multiple replication bubbles (Fig. 63.3) Single replication bubble (Fig. 63.4)... 

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