co-transfection- how does it work?

[Ammie]

Earlier, I did a project as a part of my education where I did co-transfection with two plasmids, one containing GFP and one the gene of interest.

The GFP was the transfection control and we only looked closer to the cells that were green and the theory was that the cells that took up the GFP-plasmid most likely also took up the other plasmid (or plasmids- sometimes I did a triple-transfection).

Now I have been thinking a lot of this and how does that work? When is this true? And how much can I trust it?

Is it that if you use a method like lipofectamin you create small liposomes that contains a lot of plasmid and that it is very likely that both plasmid is in this liposomes? And therefore get into the cell?

In that case it would not be true for transfection using electroporation, where it would be completely random (?).

And what if I have a very large second plasmid beside the GFP, can I still trust it to be successfully transfected? Could it be that the liposomes exclude one of the plasmids?

How should I think here???