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- Discussion:
     - precursor of structural protein fibrin & is composed of duplicate sets of three chains (Aalpha, Bbeta, and gamma) linked by disulfide bonds;
     - peptide-bond cleavage of fibrinopeptide A and fibrinopeptide B yields soluble fibrin;
     - fibrin rapidly polymerizes into fibrin strands, ultimately forming fibrin clot that mechanically impedes blood loss