The near-edge x-ray absorption (NEXAFS) spectra at the carbon K edge of the five amino acids, glycine, phenylalanine, histidine, tyrosine, and tryptophan, have been computed by the ab initio static-exchange method and compared to recently collected experimental data. The analysis of the spectra is carried out on the basis of a building-block decomposition taking advantage of the separate spectra for each carbon center. It is shown that different subunits can be clearly identified by such an analysis and that their spectral features remain largely unperturbed in the different molecules. The results support the suggestion by Boese et al. [J. Electron. Spectrosc. Relat. Phenom. 85, 9 (1997)] that differences in the NEXAFS spectra might be used for mapping proteins which differ in their amino acid content.