Which of the following best describes an enzyme linked immunosorbent assay (ELISA)?

An enzyme linked immunosorbent assay (ELISA) is best described as a technique to detect and quantify specific proteins. This is accomplished through the use of antibodies that specifically bind to the target proteins of interest. When the target protein is present, the bound antibody can be linked to an enzyme that produces a measurable signal, such as a color change, upon substrate addition. This allows for both the detection and quantification of the protein based on the intensity of the signal generated.

In contrast, the other choices do not accurately reflect the purpose and methodology of ELISA. Determining protein sequences is related to techniques such as mass spectrometry or amino acid sequencing, which analyze the specific order of amino acids in proteins. Separating nucleic acids pertains to methods like gel electrophoresis, which is used to analyze DNA or RNA rather than proteins. Cloning DNA involves techniques such as polymerase chain reaction (PCR) and recombinant DNA technology, which are unrelated to the detection of proteins. Therefore, the focus on protein detection and quantification clearly aligns ELISA with choice B.