You have identified a novel cytoplasmic protein You have identified a novel cytoplasmic protein. Sequence analysis revealed the presence of a number of potential serine/threonine amino acids that are potential phosphorylation sites. Based on this data, you hypothesize that this protein may be a substrate for a  A. protein kinase. B. receptor tyrosine kinase. C. G-protein-coupled receptor. D. ADP-ribosylase.   Why is phosphorylation-dephosphorylation commonly used to regulate signal transduction pathways?  A. Phosphate groups can be used as efficient second messengers. B. Protein kinases and phosphatases are abundant in most cells. C. The hydrolysis of bound GTP results in GDP and Pi. D. The addition or removal of a phosphate group can cause changes in a protein’s shape/function.  In a particular growth factor induced signal transduction pathway, which of the following proteins phosphorylates MAP kinase kinase?  A. MAP kinase B. MAP kinase kinase C. MAP kinase kinase kinase D. MAP phosphatase 

The protein SOS is a guanine nucleotide exchange factor for Ras, a monomeric G Protein. SOS helps facilitate the exchange of GDP for GTP. What would be the effect of a mutation that inhibits the interaction between SOS and Ras?   A.  GTP would remain bound to Ras, thereby disrupting downstream signaling events. B.  GDP would remain bound to Ras, thereby disrupting downstream signaling events. C.  GTP would remain bound to Ras, leading to overstimulation of the Ras pathway. D.  GDP would remain bound to Ras, leading to overstimulation of the Ras pathway. You are planning to perform some protein-protein interaction studies to identify a receptor for a steroid hormone you have been working on. With which of the following types of cell extracts should you begin?  A. plasma membrane B. extracellular C. cytoplasmic D. nuclear  

  A mutation in the DNA binding domain of a steroid hormone receptor is most likely to affect the  A. conformational change of the receptor. B. binding of the hormone to the receptor. C. translocation of the receptor to the nucleus. D. cellular response to the hormone. In response to a particular GPCR-mediated signaling event, if the enzymatic activity of the effector protein, phospholipase C, was blocked and failed to cleave phosphatidylinositol-4,5-bisphosphate (PIP2) into its two products (IP3 and DAG), which of the following signal transduction processes would most directly be affected?  A. the exchange of GDP for GTP on a G protein. B. the release of Ca++ from the endoplasmic reticulum. C. the GPCR binding to signal (ligand). D. the activation of protein kinase A by cAMP.