In addition to use as the metric notation of pico (10^-9), it is commonly used to indicate the logarithm of a reciprocal, e.g. pK_a=log(1/K_a). When seen as a prefix followed by a number, p indicates molecular mass determined from a Laemmli gel and characterises a protein whose identity is otherwise unknown, e.g. p53, a protein of mass 53000Da. It is also used as a prefix to an alphanumeric designation of a plasmid, e.g. pVA50. In nucleic acid chemistry it denotes an orthophosphate in a 5'- or 3'-phosphomonoester bond (e.g. pA or Gp), a phosphodiester bond (e.g. CpG), or a phosphate anhydride bond (e.g. ppA). In genetics it is a designation of a location in the short arm of a chromosome.