Which of the following forms the C5 convertase in the Lectin/Classic pathway?

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Multiple Choice

Which of the following forms the C5 convertase in the Lectin/Classic pathway?

Explanation:
In the lectin and classical pathways, the enzyme that initially cleaves C3 is the C3 convertase C4b2a. When a second C3b molecule binds to this complex, it becomes the C5 convertase, which is best described as C4b2a3b. This new complex can then cleave C5 into C5a and C5b to proceed with the downstream inflammatory and membrane attack steps. The other forms correspond to different stages or pathways: C3bBb is the C3 convertase of the alternative pathway; C3bBb3b is the C5 convertase of the alternative pathway when a second C3b binds; and C4b2b is not the functional C3 convertase in this context.

In the lectin and classical pathways, the enzyme that initially cleaves C3 is the C3 convertase C4b2a. When a second C3b molecule binds to this complex, it becomes the C5 convertase, which is best described as C4b2a3b. This new complex can then cleave C5 into C5a and C5b to proceed with the downstream inflammatory and membrane attack steps. The other forms correspond to different stages or pathways: C3bBb is the C3 convertase of the alternative pathway; C3bBb3b is the C5 convertase of the alternative pathway when a second C3b binds; and C4b2b is not the functional C3 convertase in this context.

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