Which coagulation factor serves as a cofactor in the common pathway and is activated by thrombin?

Which coagulation factor serves as a cofactor in the common pathway and is activated by thrombin?

• A. Factor II
• B. Factor VII
• C. Factor V
• D. Factor X

Answer: (C)

Factor V acts as a cofactor in the common pathway and is activated by thrombin to form Factor Va. Once activated, Va teams up with Factor Xa on a phospholipid surface to create the prothrombinase complex. This complex efficiently converts prothrombin (Factor II) into thrombin, propelling the cascade toward fibrin formation. The question is asking for the cofactor in the common pathway that thrombin activates, which is exactly the role of Factor V. By contrast, Factor II is the substrate that thrombin converts, not a cofactor; Factor VII initiates the extrinsic pathway; Factor X is a protease (Xa) in the common pathway, not a cofactor.

Factor V acts as a cofactor in the common pathway and is activated by thrombin to form Factor Va. Once activated, Va teams up with Factor Xa on a phospholipid surface to create the prothrombinase complex. This complex efficiently converts prothrombin (Factor II) into thrombin, propelling the cascade toward fibrin formation. The question is asking for the cofactor in the common pathway that thrombin activates, which is exactly the role of Factor V.

By contrast, Factor II is the substrate that thrombin converts, not a cofactor; Factor VII initiates the extrinsic pathway; Factor X is a protease (Xa) in the common pathway, not a cofactor.