View this video/animation to see how one type of immune cell-the helper T cell-interprets a message presented at the surface of the cell membrane. The message is an antigen, a protein fragment taken from an invading microbe. A series of events unfolds that results in the production of many clones of the helper T cell. These identical T cells can serve as a brigade forming an essential communication network to activate B cells, which make antibodies that will specifically attack the activating antigen. [4.21]

Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Explain how the binding of a ligand initiates signal transduction throughout a cell
Recognize the role of phosphorylation in the transmission of intracellular signals
Evaluate the role of second messengers in signal transmission

This pathway provides an introduction to cellular mechanisms of communication, highlighting one of the primary mechanisms: signal transduction pathways. For a deeper look at this topic, we recommend the pathway Cell Communication from the OpenStax textbook Biology for AP® Courses.

Genes are turned on and off in many ways. This article covers chemical signal transduction. Article includes animations, pictures, video, biographical information, and quiz questions that are accessed by clicking on buttons along the bottom of the page.