molecular biology

This term refers to a specialized scientific discipline. In academic and professional contexts, it is treated as a field of study rather than a countable object. It describes the intersection of genetics and biochemistry, focusing on the chemical structures of macromolecules.

Because it denotes a specific branch of science, it is an uncountable noun. One does not refer to "a molecular biology" or "molecular biologies" when discussing the field itself, but rather uses partitives like "a course in molecular biology" or "a degree in molecular biology" to specify a particular instance of study.