  We calculate the partonic structure of a constituent quark in the
Next-to-Leading Order framework. The structure of any hadron can be obtained
thereafter using a convolution method. Such a procedure is used to generate the
structure function of proton and pion in NLO, neglecting certain corrections to
$\Lambda_{QCD}$. It is shown that while the constituent quark structure is
generated purely perturbatively and accounts for the most part of the hadronic
structure, there is a few percent contributions coming from the nonperturbative
sector in the hadronic structure. This contribution plays the key role in
explaining the SU(2) symmetry breaking of the nucleon sea and the observed
violation of Gottfried sum rule. These effects are calculated. We obtained an
Excellent agreement with the experimental data in a wide range of $x=[10^{-6},
1]$ and $Q^{2}=[0.5, 5000]$ $GeV^{2}$ for the proton structure function. We
have also calculated Pion structure and compared it with the existing data.
Again, the model calculations agree rather well with the data from experiment.
