In this paper, we present the results of a comparative study of the modification of the temperature dependences of the normal-state Nernst coefficient, Q, under praseodymium doping for two sample series of the Y1-xPrxBa2Cu3Oy and Y0.85-xPrxCa0.15Ba2Cu3Oy compositions. Peculiarities of the Q(T) and Q300 K(x) dependences induced by the presence of additional calcium ions in the YBa2Cu3Oy lattice are revealed and analyzed. It is shown that both the Q(T) dependences and the thermopower temperature dependence obtained earlier for the same samples can be fully described on the basis of a narrow-band model. The values of the charge-carrier mobility and the degree of a dispersion law asymmetry are determined by the quantitative analysis of the experimental results. The presence of additional calcium ions in the lattice is shown to not influence a variation of the dispersion law asymmetry with increasing praseodymium doping but to affect strongly the mobility behavior. The observed dependence of the mobility on the doping level in both investigated systems, as well as a difference in variation of the thermopower and Nernst coefficient values in the Y0.85-xPrxCa0.15Ba2Cu3Oy system are explained based on analyzing mechanisms of the influence of the energy spectrum parameters on the mobility value in the YBa2Cu3Oy system.