Final answer:
If a specific kind of protein is not continually used by a cell, the gene for that protein is turned on and off at different times, rather than constantly transcribed and translated into protein.
Step-by-step explanation:
Gene expression is a highly regulated process where only the genes that are needed by a cell are 'turned on' or expressed. This means that if a specific kind of protein is not continually used by a cell, the gene for that protein is not constantly transcribed and translated into protein. Instead, the gene is regulated and turned on and off at different times, depending on when the protein is needed by the cell.