for rna in cell.species_types.get(__type=wc_kb.prokaryote.RnaSpeciesType):
            rna_specie = rna.species.get_or_create(compartment=cytosol)
            conc = round(abs(random.normal(loc=mean_rna_copy_number,scale=15))) / scipy.constants.Avogadro / mean_volume
            cell.concentrations.get_or_create(id='CONC({})'.format(rna_specie.id), species=rna_specie, value=conc, units=unit_registry.parse_units('M'))