Purpose. The article is devoted to brief exposition of methodics of description of potential electron scattering on complex molecules. In the Additivity Rule approach the differential and integral cross-sections of elastic electron scattering by amino acids biomolecules, threonine and tyrosine are calculated. Methods. Expressions for amplitudes and cross sections of electron scattering on molecules in the independent atoms model were given. The Additivity Rule approach was described. Expressions for amplitudes and differential cross sections of electron scattering on the atoms of which the molecule consists were given. The scattering phase shifts are calculated in the optical potential method of the ELSEPA program. Results. Amplitudes, differential and integral cross sections of elastic electron scattering on hydrogen, carbon, nitrogen, oxygen atoms and on amino acid biomolecules of threonine and tyrosine were calculated. The graphical comparison of angular, for differential, and energy, for integral, dependencies of scattering cross sections by molecules showed a qualitative similarity of their behavior. Conclusions. The expressions and the accompanying concepts necessary for calculation of the cross sections of elastic electron scattering by complex molecules were considered. The independent atoms model and the Additivity Rule approach used for this were summarized. Using the ELSEPA program, the amplitudes and cross sections of the elastic electron scattering by the H, C, N, O atoms, which are components in the structure of the amino acids threonine and tyrosine biomolecules, were calculated. The differential cross section of electron scattering on these biomolecules is characterized by a wide minimum due to the electron scattering by the carbon and oxygen atoms. The main contribution to this cross section is given by electron scattering on carbon, oxygen and hydrogen atoms and to integral cross sections from the electron scattering on hydrogen and carbon atoms

Keywords: independent atom model, amplitude, phase shifts, molecule, optical potential, cross section