The RNA in telomerase is binded to a complementary sequence on DNA specifically to 3' G overhang and also the Nucleotides associated to RNA component of telomerase are binded to DNA at the 3 end. Now the Telomerase moves through DNA strand that is newly synthesized towards the 3 end. In the same way if there are any additional nucleotides they were all binded to 3 end of the DNA and then the telomerase is removed from the DNA completely. now to fill in the gap left by telomerase the synthesis occurs on the 5 end of DNA strand.
