DNA Replication, Recombination, Repair II

This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to ecampus.oregonstate.edu for the rest of the courses see www.youtube.com 1. 1.DNA polymerase I has three enzymatic activities - a 5' to 3' DNA polymerase activity, a 3' to 5' exonuclease activity (also called proofreading), and a 5' to 3' exonuclease activity. 2. All DNA polymerases require a primer to start DNA synthesis. The primer is formed inside of cells by a special RNA polymerase known as primase. (RNA polymerase does not require a primer) 3. DNA replication proceeds by two distinct mechanisms (both 5'-3', however)- one on each strand. Leading strand and lagging strand synthesis occur by different mechanisms, but both are catalyzed by the same DNA replication complex (Pol III, in the case of E. coli). 4. Leading strand synthesis is continuous in the 5' to 3' direction. Lagging strand synthesis can only occur when the leading strand synthesis opens up a new single stranded region for replication. The 5' to 3' syntheses of the lagging strand are discontinuous. The many pieces of lagging strand synthesis are called Okazaki fragments. 5. Okazaki fragments must be combined together ultimately. First, the RNA primer must be removed from each one. The 5' to 3' exonuclease activity of DNA Polymerase I is needed to remove the initial RNA primer of leading strand synthesis, but is needed frequently to remove the primers of ...