We use the density functional theory to demonstrate that the chemical reactivity of nitrogen atoms with a propagating zigzag edge during the nucleation of graphene grains can give rise to persistent sublattice symmetry breaking phenomena. Their effect on the electronic structure of a formed two-dimensional graphene sheet is studied by unfolding the bands obtained from large supercell calculations. We argue that the loss of inversion symmetry enhances the creation of a band gap when assisted by dopant agglomeration. At higher concentrations of graphitic nitrogen the conduction band gets strongly suppressed, paving the way for the use of nitrogen-doped graphene as a valley-filter component.