Fig 10-1 Figure: 10-01 Caption: Generalized model of semiconservative replication of DNA. New synthesis is shown in teal.

Fig 10-2 Figure: 10-02 Caption: Results of one round of replication of DNA for each of the three possible modes by which replication could be accomplished.

Fig 10-3 Figure: 10-03 Caption: The Meselson–Stahl experiment.

Fig 10-4 Figure: 10-04 Caption: The expected results of two generations of semiconservative replication in the Meselson–Stahl experiment.

Fig 10-5 Figure: 10-05 Caption: The Taylor– Woods–Hughes experiment, demonstrating the semiconservative mode of replication of DNA in root tips of Vicia faba. A portion of the plant is shown in the top photograph. (a) An unlabeled chromosome proceeds through the cell cycle in the presence of 3H-thymidine. As it enters mitosis, both sister chromatids of the chromosome are labeled, as shown by autoradiography. After a second round of replication (b), this time in the absence of 3H-thymidine only one chromatid of each chromosome is expected to be surrounded by grains. Except where a reciprocal exchange has occurred between sister chromatids (c), the expectation was upheld. The micrographs are of the actual autoradiograms obtained in the experiment.

Fig 10-6 Figure: 10-06 Caption: Bidirectional replication of the E. coli chromosome. The thin black arrows identify the advancing replication forks. The micrograph is of a bacterial chromosome in the process of replication, comparable to the figure next to it.

Fig 10-7 Figure: 10-07 Caption: The chemical reaction catalyzed by DNA polymerase I. During each step, a single nucleotide is added to the growing complement of the DNA template, using a nucleoside triphosphate as the substrate. The release of inorganic pyrophosphate drives the reaction energetically.

Fig 10-8 Figure: 10-08 Caption: Demonstration of 5' to 3' synthesis of DNA.

Fig 10-10 Figure: 10-10 Caption: Helical unwinding of DNA during replication as accomplished by DnaA, DnaB, and DnaC proteins. Initial binding of many monomers of DnaA occurs at DNA sites containing repeating sequences of 9 nucleotides, called 9mers. Not illustrated are 13mers, which are also involved.

Fig 10-11 Figure: 10-11 Caption: The initiation of DNA synthesis. A complementary RNA primer is first synthesized, to which DNA is added. All synthesis is in the 5'-to-3' direction. Eventually, the RNA primer is replaced with DNA under the direction of DNA polymerase I.

Fig 10-12 Figure: 10-12 Caption: Opposite polarity of DNA synthesis along the two strands, necessary because the two strands of DNA run antiparallel to one another and DNA polymerase III synthesizes only in one direction (5' to 3'). On the lagging strand, synthesis must be discontinuous, resulting in the production of Okazaki fragments. On the leading strand, synthesis is continuous. RNA primers are used to initiate synthesis on both strands.

Fig 10-13 Figure: 10-13 Caption: Illustration of how concurrent DNA synthesis may be achieved on both the leading and lagging strands at a single replication fork. The lagging template strand is “looped” in order to invert the physical direction of synthesis, but not the biochemical direction. The enzyme functions as a dimer, with each core enzyme achieving synthesis on one or the other strand.

Fig 10-14 Figure: 10-14 Caption: Summary of DNA synthesis at a single replication fork. Various enzymes and proteins essential to the process are shown.

Fig 10-17 Figure: 10-17 Caption: Diagram illustrating the difficulty encountered during the replication of the ends of linear chromosomes. A gap (--b--) is left following synthesis on the lagging strand.

Fig 10-18 Figure: 10-18 Caption: The predicted solution to the problem posed in Figure 10–17. The enzyme telomerase directs synthesis of the TTGGGG sequences, resulting in the formation of a hairpin structure. The gap can now be filled, and, following cleavage of the hairpin structure, the process averts the creation of a gap during replication of the ends of linear chromosomes.

From TA Brown, “Genomes,” 2nd ed

From TA Brown, “Genomes,” 2nd ed