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You asked this a while ago, but if you are still interested I will now answer it! Proinsulin is a hormone which is a precursor to insulin. It is produced in the beta-cells of the pancreas, and it is later modified by the golgi apparatus, to become insulin. Assay development is the development of a test (aka assay) of particular biomarkers. And I presume clincal application simnply refers to using this information in a clincal setting, ie. on patients. Antibody production is when your immune system recognises something foriegn and potentially harmful, and it prodcues antibodies against it. In science, we can get an animal to produce a certain antibody to a particular protein, and we can use this for imaging purposes.
you would get on well with my mum :L
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