  The alternative to the standard formulation of the quark-parton model is
proposed. Our relativistically covariant approach is based on the solution of
the master equations relating the structure and distribution functions, which
consistently takes into account the intrinsic quark motion - in
contradistinction to the standard infinite momentum approach, in which this
motion is latently suppressed. The model well reproduces the experimental data
on the both polarized and unpolarized structure functions, assuming that only
the valence quarks term contributes to the nucleon spin. It is shown, the
combined analysis of the polarized and unpolarized data can give an information
about the effective masses and intrinsic motion of the quarks inside the
nucleon. Simultaneously, it is shown that the rate of the nucleon energy
carried by the quarks can be less, than estimated from the standard approach.
As an addition, a prediction for the proton spin function $g_2$ is given.
