BIOLOGY Lecture Notes - Complement Membrane Attack Complex, C5-Convertase, Complement System
Document Summary
The complement system: classical pathway and formation of membrane attack complex, the classical pathway is one of the three pathways that make up the complement system, which is an essential part of the immune system. The classical pathway is activated by the binding of antibodies to the surface of pathogens, such as bacteria or viruses. The antibody molecule is usually of the igm or igg class. When the antibody binds to the antigen, it undergoes a conformational change that exposes a binding site for the c1 complex: the c1 complex is a collection of three different proteins: c1q, c1r, and c1s. When the c1 complex binds to the antibody-antigen complex, it activates c1r, which in turn activates c1s. Activated c1s cleaves c4 and c2 into smaller fragments, c4a and c2a. The c2a fragment combines with c4b to form the c3 convertase, which cleaves c3 into c3a and c3b: c3b is the most important component of the classical pathway.
