Relication and Transcription

549 Words3 Pages
Describe each process (including differences between bacteria and eukaryotes) and explain the significance of the differences between replication and transcription When first going through DNA replication, the two strands of double helix unwind. Each strand is an outline for the formation of a new, complementary strand. DNA helicase enzymes hang along the DNA molecule, opening the double helix as they move. Once the strands are separated, helix-destabilizing proteins bind to single DNA strands, preventing re-formation of the double helix until the strands are copied. Enzymes called topoisomerases produce breaks in the DNA molecules and then reconnect the strands, relieving strain and effectively preventing tangling and knotting during replication. DNA polymerase adds new nucleotides to a growing strand of DNA. Because DNA polymerase must adhere to an existing template, an RNA primer is first created at the site of replication. The RNA primer is synthesized by primase, an enzyme that is able to start a new strand of RNA opposite a DNA strand. After a few nucleotides have been added, the primase is displaced by DNA polymerase, which can then add subunits to the 3’ end of the short RNA primer. Because DNA synthesis always proceeds in a 5’ to 3’ direction, one DNA strand (the lagging strand) must be synthesized discontinuously as short okazaki fragments. Each okazaki fragment is initiated by a separate RNA primer and then is extended toward the 5’ end of the previously synthesized fragment by DNA polymerase. When the RNA primer of the previously synthesized fragment is reached, the primer is degraded and replaced with DNA by the action of DNA polymerase. The fragments are then joined together by DNA ligase, an enzyme that links the 3’ OH of one DNA fragment to the 5’ phosphate of another, forming a phosphodiester linkage. The opposite strand, the leading strand,

More about Relication and Transcription

Open Document