code: public static Atom[] getRepresentativeAtomArray(Structure s) {
  
  		List<Atom> atoms = new ArrayList<Atom>();
  
  		for (Chain c : s.getChains()) {
  			Atom[] chainAtoms = getRepresentativeAtomArray(c);
  			for (Atom a : chainAtoms) {
  				atoms.add(a);
  			}
  		}
  
  		return atoms.toArray(new Atom[atoms.size()]);
  	}
docs: Gets a representative atom for each group that is part of the chain
  backbone. Note that modified aminoacids won't be returned as part of the
  backbone if the {@link org.biojava.nbio.structure.io.mmcif.ReducedChemCompProvider} was used to load the
  structure.
  
  For amino acids, the representative is a CA carbon. For nucleotides, the
  representative is the {@value #NUCLEOTIDE_REPRESENTATIVE}. Other group
  types will be ignored.
  
  @param s
  Input structure
  @return representative Atoms of the structure backbone
  @since Biojava 4.1.0