Strange and charmed quarks in the nucleon

We discuss the general method of the calculation of the nucleon matrix elements of an operator associated with nonvalence quarks. The method is based on the QCD sum rules and low energy theorems. As an application of these considerations, we calculate the strange quark matrix element as well as the momentum distribution of the strangeness in the nucleon. We also calculate the singlet axial constant associated with ${\eta }^{\prime }$ meson as well as an axial constant associated with heavy quarks.