Final Answer:
The C3 convertase is formed through the classical, lectin, or alternative pathway, while the C5 convertase is formed through the action of C3 convertase on C5.
Step-by-step explanation:
The complement system is a crucial part of the immune system, consisting of a complex network of proteins that work together to eliminate pathogens. The C3 convertase is formed through different pathways - classical, lectin, or alternative. In the classical pathway, it is formed by the binding of C1q to antigen-antibody complexes, leading to the activation of C4 and C2 to form C3 convertase (C4b2a). In the lectin pathway, mannose-binding lectin binds to carbohydrates on pathogen surfaces, activating MASP-2 which then cleaves C4 and C2 to form C3 convertase. In the alternative pathway, spontaneous hydrolysis of C3 leads to the formation of C3bBb which acts as a C3 convertase.
On the other hand, the C5 convertase is formed through the action of C3 convertase on C5. Once C3b binds to C3 convertase (C4b2a or C3bBb), it forms a complex that can cleave C5 into C5a and C5b. This process initiates the formation of the membrane attack complex (MAC) and leads to cell lysis.
Understanding these pathways and their components is essential in comprehending the intricate workings of the complement system and its role in immune response.