Question

Src (a protein kinase), and PTPB1 (a protein phosphatase) both change the phosphorylated status of the same substrate (substrate X).  Constitutive phosphorylation of substrate X (i.e. it is always phosphorylated) promotes cell migration and is associated with certain forms of metastatic cancer (i.e. able to spread to distant parts of the body) in humans.  

Which of the following mutations in a patient would you predict to be associated with increased risk for developing metastatic cancer?  

1. An activating mutation in the gene encoding Src.
2. A deactivating mutation in the Src.
3. An activating mutation in the gene encoding PTPB1.
4. A deactivating mutation in the gene encoding PTPB1.

During signal transduction, a signal (information) is converted into a biochemical change.  Where does the signal originate?

1. Inside of the cell
2. Outside of the cell

Answer 1

1. d. A deactivating mutation in the gene encoding PTPB1.

As we know Src is protein kinase and PTPB1 is a protein phosphatase. Both proteins are necessary for regulation of phosphorylation. We know that phosphorylated substrate X promotes cell migration and is associated with certain forms of metastatic cancer. If substarte is constitutively phosphorylated it means protein phosphatase doesn't work properly. From available options, we can say that there is a deactivating mutation in protein phosphatase (PTPB1) encoding gene. Due to this mutation gene is inactivated and unable to form functional protein phosphatase, consequently constitutive phosphorylation occur.

2. b. Outside of the cell.

During signal transduction, a signal (information) is converted into a biochemical change. When a ligand binds to the outside of the transmembrane receptor, it induces a conformational change in the cytoplasmic part of receptor. Consequently a cascade of signalling pathways start and signal transduction takes place.