Subject: Electrical Signals in DNA

I have come accross a lot of material and research about the conductvity of 
DNA. Although it is still not clear what kind of conductor the DNA molecule 
is, I have observed that in all the experiments the electrical signal was 
applied externally and a variety of different setups. I would like to ask that 
is there any electrical signal coursing throught the DNA molecules in reality 
[as in, naturally]? On what basis do the researchers decide that the signal 
applied should be a.c. or d.c, its frequency and other such characteristics?

Re: Electrical Signals in DNA