Final answer:
In a protein microarray, the type of molecule used to measure protein expression is antibodies. Antibodies specifically bind to target proteins on the array and their interactions are detected, typically through fluorescent tagging, allowing for the quantification of protein levels.
Step-by-step explanation:
The molecule used in a protein microarray to measure protein expression is d) Antibodies. Protein microarrays rely on antibodies to capture and detect proteins. These antibodies bind specifically to the proteins of interest, allowing for the assessment of protein expression levels. The antibodies are fixed onto a slide and are used to probe a sample containing proteins, where each antibody is specific to a different target protein. When proteins from the sample bind to their corresponding antibodies on the array, this interaction can be detected and measured, usually by using a fluorescent tag that emits light when excited, indicating the presence and quantity of the protein.
mRNA, ribosomal RNA (rRNA), and transfer RNA (tRNA) are all different types of RNA involved in the central dogma of molecular biology, which relates to gene expression. However, they are not used in protein microarrays. mRNA is the single-stranded transcript of DNA that codes for proteins, but it is not used for the protein capture step in microarrays; instead, it may be used in methods like Northern blotting or in DNA microarrays for gene expression profiling. Antibodies are the molecules that serve as the basis for detecting proteins on the protein microarray.