DNA is a material that has the potential to be used in nanoelectronic devices as an active component. However, the electronic properties of DNA responsible for its conducting behaviour remain controversial. Here we use a self-consistent quantum molecular dynamics method to study the effect of DNA structure and base sequence on the energy involved when electrons are added or removed from isolated molecules and the transfer of the injected charge along the molecular axis when an electric field is applied. Our results show that the addition or removal of an electron from DNA molecules is most exothermic for poly(dC)-poly(dG) in its B-form and poly(dA)-poly(dT) in its A-form, and least exothermic in its Z-form. Additionally, when an electric field is applied to a charged DNA molecule along its axis, there is electron transfer through the molecule, regardless of the number and sign of the injected charge, the molecular structure and the base sequence. Results from these simulations provide useful information that is hard to obtain from experiments and needs to be considered for further modelling aiming to improve charge transport efficiency in nanoelectronic devices based on DNA.