Question

Outline the mechanism of prothrombin activation. .

State the general mechanisms for the control of clotting and explain the specific role of antithrombin III in the clotting cascade. Describe the effect of heparin on antithrombin III.

Describe the lysis of fibrin clots by plasmin and the activation of plasminogen by tissue-type plasminogen activator (TPA).

Answer 1

Prothrombin activation is prothrombinase so that prothrombinase is consist of the serine protease, Factor xa, Factor va and protein co-factor in which negatve charges present in the outer membrane of the cell. The prothrombinase complex catalyzes the conversion of prothrombin, an inactive zymogen, to thrombin an active serine protease to thrombin, an active serine protease. The activation of thrombin is a critical reaction in the coagulation cascade, which functions to regulate hemostasis in the body.

Mechanism if the clotting- it is a physiochemical change bywhich the liquids blood is converted into a jelly-like mass, called clot. it ia a complex process and requires interaction of various factors.

The process of coagulation is aconversion of the fibrinogen into fibrin monomer after removal of two pairs of polypeptides, fibrinopeptide A and fibrinopeptide B. The fibrin monomers then polymerise to form fibrin threads. These threads form a meshwork in which the RBCs are entangled to form the blood clot. The fibrin threads which are formed initially are soft and friable.

Antithrombin III is a nonvitamin k- dependent protease that inhibits coagulation by neutralizing the enzymatic activity of thrombin ( factors IIa,IXa, Xa) Anti thrombin III activity is markedly potential by haparin , the principal mechanism by which both heparin and low- molecular - weight heparin result in anticoagulation.