Cellular signaling, otherwise known as signal transduction, is the mechanism by which cellular context and environmental situation are used to regulate or adjust cellular behavior. Multicellular organisms use cellular signaling to coordinate responses to the environment, facilitate development, and maintain homeostasis. The mechanisms by which a cell receives a message and translates it into short-term or long-term effects are as varied as the responses stimulated by cellular signaling. There are, however, some generalized steps that can be applied to many different signaling situations. This case study uses insulin signaling and the pathological case of diabetes as a lens through which students will learn general signaling mechanisms like kinase cascades and second messenger pathways. The case is designed in the interrupted format and has three parts that could be used either as homework or as an in-class activity. It is written for use in a cell biology class for sophomore or junior undergraduates but could also be utilized in biochemistry, physiology, or genetics courses.