code: public static List<Group> getAminoAcids(Chain chain) {
  
  		List<Group> gs = new ArrayList<>();
  
  		for ( Group g : chain.getAtomGroups()){
  
  			if ( g.isAminoAcid())
  				gs.add(g);
  
  		}
  
  		return gs;
  
  	}
docs: Get all amino acids in a chain.
  @param chain
  @return