Use This Description to Answer the Following Question

Multiple Choice

Use this description to answer the following question.
A major group of G-protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.
-Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because

A) they are species specific.
B) they always lead to the same cellular response.
C) they amplify the original signal manifold.
D) they counter the harmful effects of phosphatases.
E) the number of molecules used is small and fixed.