Explain why one molecule of IgM can activate complement but it takes about 1000
molecules of IgG on a cell surface to activate complement.
What will be an ideal response
Complement is activated by the classic pathway when antigen binds to antibody, altering the structure of the
antibody to reveal the C1q binding site. In order for C1q to be activated, it must be bound to two adjacent C1q
binding sites. Thus, if two IgG molecules are close together, C1q is activated. IgM, because of its pentameric
structure, naturally has two C1q binding sites adjacent, and one molecule of IgM can easily activate complement.
Since IgG is a monomer and single IgG cannot activate complement, a cell must be coated with enough IgG to
eventually put two IgG molecules in close proximity. Statistically, it takes about 1000 IgG molecules to bind to the
cell before two molecules are sufficiently close enough.
You might also like to view...
Migraine symptoms are thought to be related to amplification of nociceptive signals in which pathway?
A. Cranial nerve (CN) VII relay to spinal nucleus of thalamus B. Spinothalamic pathway C. Trigeminothalamocortical pathway D. Fasciculus cuneatus relay to medial lemniscus E. None of the above
In the term extracorporeal, the combining form corpor/e means:
A) body. B) circulation. C) beyond. D) constriction.
A medical word can only contain one prefix
Indicate whether the statement is true or false
The health care provider prescribes which of the following to stop bleeding?
A. hemostatics B. coagulants C. thrombolytics D. anticoagulants