Based on large-scale shell model calculations we have determined the electron capture, positron capture and beta-decay rates on more than 100 nuclei in the mass range A=45-65. The rates are given for densities \rho Y_e =10^7-10^{10} mol/cm^3 and temperatures T=10^9-10^{10} K and hence are relevant for both types of supernovae (Type Ia and Type II). The shell model electron capture rates are significantly smaller than currently assumed. For proton-to-baryon ratios Y_e=0.42-0.46 mol/g, the beta-decay rates are faster than the electron capture rates during the core collapse of a massive star.