Cascade order in classical activation once activated, the complement cascade is an ordered process. each reaction leads to another reaction. this activity asks you to place the cascade reactions in the order they occur, starting with the c1.

1) c1 interacts with an antibody that is bound to a pathogen
2) c3 is split into c3a and c3b
3) c2a and c4b combine to form an enzyme
4) c1 cleaves c2 and c4

Answer :

1) C1 interacts with and antibody that is bound to pathogen

2)C1 cleaves C2 and C4

3)C2a and C4b combine to form an enzyme

4)C3 is split into C3a and C3b

Explanation:

Classical pathway is activated by antigen antibody complex indicating the proteolytic cleavage of the molecule. C1 is activated by this complex and the activated C1 acts on C2 AND C4 to for an enzyme C3 convertase (C4b,2b).This enzyme then acts on C3 and causes it to cleave into C3 and C3b.