All DNA polymerases synthesize new DNA strands in the 5’→3’ direction. In some respects, replication of the antiparallel strands of duplex DNA would be simpler if there were also a second type of polymerase, one that synthesized DNA in the 3’→5’ direction. The two types of polymerase could, in principle, coordinate DNA synthesis without the complicated mechanics required for lagging strand replication; however, no such enzyme has been found. Suggest a possible mechanism for 3’→5’ DNA synthesis (show the electron pushing-you may use abbreviated structures). Pyrophosphate should be one product. If the 3’→5’ polymerase existed, could your mechanism be supported in a cell (why or why not)? [You may suggest the use of DNA precursors not actually present in extant cells.]
