What converts fibrinogen to fibrin?
Precursor of thrombin is produced in liver and is called prothrombin. Gene for coding of prothrombin is located on chromosome #11. Few coagulation factors and vitamin K act on prothrombin to convert it into thrombin.
Thrombin acts as an enzyme and almost half in molecular weight compared to prothrombin. Thrombin transforms soluble plasma protein fibrinogen into insoluble polymer called fibrin.