Describe in detail the key enzymes an mechanisms involved in DNA replication. Include in your answer a discussion of the differences between prokaryote and eukaryote DNA replication. Also include in your answer a discussion of the role of telomerase in

DNA REPLICATION

The process of DNA replication follows a semi-conservative scheme which generates a double helical strand that is composed of one original and one new DNA strand . The semi-conservative scheme of DNA replication was finalized after several years of analysis of the DNA molecule . In to solve the topological problem of unwinding the DNA double helix in for the process of DNA replication to proceed , DNA topoisomerases are needed in to break and reunite the two strands of the DNA helix . There are three types of DNA topoisomerases that may be

involved in DNA replication (Champoux , 2001 . Type IA topoisomerases induce a single break in one of the two strands of the DNA molecule and the second DNA strand passes through the gap that is formed . The two broken ends of the DNA strand that was nicked are reunited after the second DNA strand has passed through it . Type IB topoisomerases also follow a similar method as Type IA topoisomerases but the specific details are somewhat different . Type II isomerases induce two breaks in the DNA double helix which in turn result in a gate through which another part of the DNA molecule can pass through . DNA topoisomerases unwind the DNA strand and counteract the excessive winding that may result if a replication fork is to be created . Thus DNA topoisomerases unzip the double helix in for the rest of the enzymes to attach to the replication fork . Gyrases are another type of enzymes involved in DNA replication among bacterial central . These enzymes relax the DNA molecule , just like DNA topoisomerases and prevent supercoiling or the tight winding of the helical structure of DNA

DNA replication involves three major phases . Initiation pertains to the identification of the key sequences on a DNA strand that designates where replication should start . Elongation involves the processes that occur at the replication fork and this is where the new DNA strand is created . Termination involves the completion of the DNA replication Another key enzyme involved in DNA replication is DNA polymerase which synthesizes new DNA strands in the 5 ( 3 ' direction . DNA polymerases often work as exonucleases which destroy nucleotides and also synthesize new nucleotides as needed . There are two types of exonucleases that work with DNA polymerases . The 3 ( to 5 ' exonuclease activity is present in both bacterial and eukaryotic DNA polymerases and this capability allows proofreading of the new nucleotides that are integrated into the new DNA strand . The 5 ( 3 ' exonuclease activity of DNA polymerases is not very common but this may be needed in to remove some part of a DNA strand during discontinuous DNA replication

Research has identified three types of DNA polymerases in bacteria DNA polymerase I is involved in the replication of the DNA strand , DNA polymerase II is responsible for the repair of DNA regions that are damaged and DNA polymerase III is associated with genome replication (Zhou and Elledge , 2000 . DNA polymerases I and II are composed on only...