XmlmmCIF equivalent: chem_comp Data items in the CHEM_COMP category give details (such as name, mass, charge, etc.) about each of the chemical components from which the relevant chemical structures can be constructed. The related categories CHEM_COMP_ATOM, CHEM_COMP_BOND, CHEM_COMP_ANGLE, etc. describe the detailed geometry of these chemical components. XmlmmCIF equivalent: chem_comp/formula The formula for the chemical component. Formulae are written according to the rules: 1. Only recognised element symbols may be used. 2. Each element symbol is followed by a 'count' number. A count of '1' may be omitted. 3. A space or parenthesis must separate each element symbol and its count, but in general parentheses are not used. 4. The order of elements depends on whether or not carbon is present. If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol. This is the 'Hill' system used by Chemical Abstracts. XmlmmCIF equivalent: chem_comp/formula_weight Formula mass in daltons of the chemical component. XmlmmCIF equivalent: chem_comp/model_details A description of special aspects of the generation of the coordinates for the model of the component. XmlmmCIF equivalent: chem_comp/model_erf A pointer to an 'external reference file', if the atomic description of the component is taken from such a file. XmlmmCIF equivalent: chem_comp/model_source The source of the coordinates for the model of the component. XmlmmCIF equivalent: chem_comp/mon_nstd_class A description of the class of a non-standard monomer, if the group represents a modification of a standard monomer. XmlmmCIF equivalent: chem_comp/mon_nstd_details A description of special details of a non-standard monomer. XmlmmCIF equivalent: chem_comp/mon_nstd_flag 'yes' indicates that this is a ";standard"; monomer, 'no' that it is ";non-standard."; Non-standard monomers should be further described using the _chem_comp.mon_nstd_parent, _chem_comp.mon_nstd_class, and _chem_comp.mon_nstd_details data items. XmlmmCIF equivalent: chem_comp/mon_nstd_parent A name of the parent monomer of the non-standard monomer, if this group represents a modification of a standard monomer. XmlmmCIF equivalent: chem_comp/mon_nstd_parent_comp_id The identifier for the parent component of the non-standard component. This data item is a pointer to _chem_comp.id in the CHEM_COMP category. XmlmmCIF equivalent: chem_comp/name The full name of the component. XmlmmCIF equivalent: chem_comp/number_atoms_all The total number of atoms in the component. XmlmmCIF equivalent: chem_comp/number_atoms_nh The number of non-hydrogen atoms in the component. XmlmmCIF equivalent: chem_comp/one_letter_code For standard polymer components, the one-letter code for the component. If there is not a standard one-letter code for this component, or if this is a non-polymer component, the one-letter code should be given as 'X'. This code may be preceded by a '+' character to indicate that the component is a modification of a standard component. XmlmmCIF equivalent: chem_comp/pdbx_component_no A serial number used by PDB in the FORMUL record. XmlmmCIF equivalent: chem_comp/pdbx_modification_details For nonstandard components a text description of modification of the parent component. XmlmmCIF equivalent: chem_comp/pdbx_synonyms Synonym list for the component. XmlmmCIF equivalent: chem_comp/three_letter_code For standard polymer components, the three-letter code for the component. If there is not a standard three-letter code for this component, or if this is a non-polymer component, the three-letter code should be given as 'UNK'. This code may be preceded by a '+' character to indicate that the component is a modification of a standard component. XmlmmCIF equivalent: chem_comp/type For standard polymer components, the type of the monomer. Note that monomers that will form polymers are of three types: linking monomers, monomers with some type of N-terminal (or 5') cap, and monomers with some type of C-terminal (or 3') cap. XmlmmCIF equivalent: chem_comp/id The value of _chem_comp.id must uniquely identify each item in the CHEM_COMP list. For protein polymer entities, this is the three-letter code for amino acids. For nucleic acid polymer entities, this is the one-letter code for the bases.