The text under the title „DNA replication “written by Brooker analyses the process in which existing DNA strands are used to make new ones. In this text author explains how the structures of DNA are involved in this process by overviewing bacterial DNA replication and some interesting features of eukaryotic DNA replication.
First chapter presents the basic characteristics of DNA replication. Process begins when two complementary strands unwind and each parental strand is used as template to synthesize new daughter strands acccording to the AT/GC rule. Those strands are identical so they contain the same information. According to the author, some scientists in the late 1950s thought of three models of DNA replication: conservative when parental strands stay together, semiconservative when the new DNA strand consists of one newly made strand and one old strand and dispersive model when DNA contains segments of both parental and newly made strands. Meselson and Stahl proved that DNA replication is semiconservative with an experiment whhere they labeled DNA with heavy and light isotopes of nitrogen and used centrifugation.
Second chapter examines how DNA replication occurs within bacteria. Synthesis begins at a single origin of replication and continues bidirectionally until two replication forks meet each other. Di
In the next paragraph it is explained that some enzymes bind to each other to form a complex. For example, the primosome is a complex between helicase and primase while the replisome is a complex between the primosome and dimeric DNA polymerase. Even though DNA replication proceeds very fast, the synthesis occurs with high fidelity. Firstly, it is result of stability of hydrogen bonding between the correct bases. Secondly, because of proofreading ability of DNA polymerase. To avoid mistakes in bacterial ce
Third chapter analyses eukaryotic DNA replication which is more complex than bacterial. For example, eukaryotic chromosomes contain not just one, but multiple origins of replication. Part of prereplication complex is formed from a group of six proteins called ORC. They initiate DNA replication. The binding of MCM helicase completes DNA replication licensing. The author points out that eukaryotes have different types of DNA polymerases with specific functions. They switch with each other during DNA replication. Another difference between bacterial and eukaryotic DNA replication is how RNA primers are removed. In eukaryotic replication enzyme called flap endonuclease is responsible for that. The ends of linear chromosomes contain telomeres and they are replicated by telomerase. It prevents chromosome shortening.
To sum up, in these three chapters the author introduced the basics of DNA replication. Later he pointed out the main differences between the bacterial DNA replication and eukaryotic DNA re