Concept Check: YST Amino Acids

Signalling cascades are frequently triggered by the binding of ligands to an extracellular binding site. These binding sites lead to conformational changes in the signaling protein and result in the phosphorylation of amino acid residues that propagate further intracellular signals. Which of the following amino acids is likely responsible for the propagation of these signals?

Phosphorylation of amino acid residues on the Bcl-2 protein results in its ability to control apoptosis and initiate cell death under appropriate conditions. Which of the following amino acid substitution is most likely to interfere with Bcl-2’s ability to regulate apoptosis effectively?