Read this passage about CFTR mutations. Then, using your knowledge of cells, select the section that describes mutations that occur at the ribosome. The CFTR gene was first discovered in 1989, but as with many research endeavors, that was only the first step. Since that first discovery, scientists have identified 1,700 mutations of the CFTR gene. These various mutations are classified according to their specific effect on the CFTR protein. Some mutations interfere with the protein assembly process. These are called protein production mutations and result in construction of incomplete or unstable proteins. Once built, the CFTR protein folds itself into a stable three-dimensional tube shape and travels to the cell membrane where it inserts itself as a channel between the cell’s interior and its surface. Mutations that affect this part of the process are called protein processing mutations. Each channel has a gate that opens and closes in response to chemical signals. Gating mutations cause misinterpretation of those chemical signals. Conduction mutations change the inside of the tunnel, making passage through the channel slower and more difficult.