Transmission properties of molecular bridges between conducting leads, especially DNA,as DNA can be synthesized in any sequence, orientation and length, trapped between the nanoeletrodes has drawn many researchers interest to understand how far and how freely charges can move along the stacks of base pairs in DNA. Considering Donor-Bridge-acceptor system, conduction properties of DNA are described in terms of attenuation parameter β and current density J(x), the β value ranges from 0.1-1.4 Å-1 for DNA and lower values of which corresponds to weak distance dependence of charge transfer and higher to strong distance dependence. Studying HOMO-LUMO distribution and energy gap, 'Critical' Bridge length Nx is determined, less than this many no. of molecules, means N < Nx, promotes super exchange tunneling transition and If N > Nx transition is through hopping. The paper also discusses the simulation of DNA based electronic components e.g. diode and transistors.