  We present an MHD shell model suitable for computation of various energy
fluxes of magnetohydrodynamic turbulence for very small and very large magnetic
Prandtl numbers $\mathrm{Pm}$; such computations are inaccessible to direct
numerical simulations. For small $\mathrm{Pm}$, we observe that both kinetic
and magnetic energy spectra scale as $k^{-5/3}$ in the inertial range, but the
dissipative magnetic energy scales as $k^{-11/3}\exp(-k/k_\eta)$. Here, the
kinetic energy at large length scale feeds the large-scale magnetic field that
cascades to small-scale magnetic field, which gets dissipated by Joule heating.
The large-$\mathrm{Pm}$ dynamo has a similar behaviour except that the
dissipative kinetic energy scales as $k^{-13/3}$. For this case, the
large-scale velocity field transfers energy to the large-scale magnetic field,
which gets transferred to small-scale velocity and magnetic fields; the energy
of the small-scale magnetic field also gets transferred to the small-scale
velocity field, and the energy thus accumulated is dissipated by the viscous
force.
