The Antibody Protein Is Often Depicted as an Uppercase Letter

Essay

The antibody protein is often depicted as an uppercase letter Y, with the two variable regions (antigen-binding domains) pointing up, and the stem consisting of the Fc region (constant domain). An analogy has been made between an antibody protein and a guided missile, with one type of antibody domain functioning as the guidance system, and the other type of domain as the 'payload.' Which antibody domain serves as the guidance system, and which as the payload? Explain your answer.