Question

Why must the C3b be close to a pathogen surface for it to be effective at binding with its thioester bond?

a) Enhances thioester reactivity
b) Prevents thioester exposure
c) Facilitates thioester cleavage
d) Inactivates thioester

Answer 1

C3b must be close to the pathogen surface for its thioester bond to effectively initiate the complement cascade, leading to pathogen opsonization and destruction by the immune system.

Step-by-step explanation:

The effectiveness of C3b in binding to pathogen surfaces via its thioester bond is due to the need for proximity to the pathogen's surface to enhance its reactivity. Once C3 is activated, the larger fragment C3b must bind to the pathogen's surface to activate the complement cascade, a critical component of the immune system's response to infections. This binding also helps in opsonization, which marks the pathogen for destruction by phagocytes like macrophages and neutrophils, enhancing the efficiency of the immune system in clearing the infection.