Pastpapers for hemostasis (open Q)

Question 1

What kind of covalent bond is formed between thrombin and antithrombin ?

Answer 1

Ester bond between active Ser and the carboxylic group of the cleaved peptide bond on antithrombin

Question 2

Which is the cofactor in the thrombin catalyzed activation of F XIII

Answer 2

Fibrin (between fibrin alpha and gamma chain)

Ca2+ is also needed

Question 3

Write down the substrates and products of the reaction catalyzed by FXIII a (Name the amino acids in the substrates and the name of the formed bond)

Answer 3

Substrate: lysine and glutamine side chains in gamma and alpha chains of fibrin
Product: gamma-glutamyl-lysine isopeptide and ammonia

Question 4

What kind of covalent bond is formed between thrombin and α2-macroglobulin ?

Answer 4

isopeptide bond between an ε–amino group of Lys on thrombin and a carboxylic group from a Gln-Cys thioester bond in α2-macroglobulin

Question 5

Which proteases are necessary for the destruction of the intrinsic tenase and the prothrombinase complexes ?

Answer 5

Thrombin (for the activation of protein C) and activated protein C for the inactivaiton of factor 5a and 8a

Question 6

Which protein cofactors are necessary for the destruction of the intrinsic tenase and the prothrombinase complexes ?

Answer 6

Thrombomodulin, protein S

Question 7

What is the mode of action of streptokinase?

Answer 7

Forms a complex with human plasminogen, in which plasminogen gains activity as plasminogen activator.
Increased fibrinolytic activity

Question 8

List two distinct functions of von Willebrand factor

Answer 8

Barrier of F VIII, mediator of platelet adhesion at high shear stress

Question 9

What is the mode of antithrombolytic action of TAFI (Thrombin activatable fibrinolysis inhibitor) ?

Answer 9

Cleaves C-terminal Lys residues and decreases the binding sites for tPA and plasminogen in fibrin and moderates the cofactor of fibrin in plasminogen activation

Question 10

How is the formation of blood coagulation inhibited in the clinic?

Answer 10

By Heparin, Vitamin K Antagonists- Coumarins (Marevan, Warfarin)

Question 11

What activates Protein C?

Answer 11

Thrombin in complex with thrombomodulin

Question 12

How is Plasmin formed?

Answer 12

From Plasminogen in the presence of Plasminogen activators.

A plasminogen activator is a serine protease which converts plasminogen to plasmin, thus promoting fibrinolysis. 2 types: tPA and uPA. Inhibited by plasminogen activator inhibitor-1 and plasminogen activator inhibitor-2.

Question 13

How is fibrinolysis terminated?

Answer 13

Alpha2- antiplasmin
Alpha2- macroglobulin
Plasmin activator inhibiting factor 1+2

Question 14

At least one drug inhibiting platelet activation

Answer 14

ASPIRIN inhibits COX1 irreversibly (converting AA to TXA2)

ADP receptor inhibitors

Question 15

Is it possible that thrombin exhibits any antithrombic effect?

Answer 15

Yeah baby! The thrombim-thrombomodulin complex activates Protein C, which inhibits Factor Va + VIIIa

Question 16

Background of activated Protein C resistance

Answer 16

The inability of Protein C to cleave Va and VIIIa, leads to hypercoagulability.

Question 17

Which diagnostic assay is based on the intrinsic pathway?

Answer 17

PTT- Partial Thromboplastin Time (Kaoulin cephalin clotting time) To detect Vit K def., vW disease, hemophilia, Hagmann factor defiency

Question 18

Kinetic significance of the phospholipid bound complexes in blood coagulation?

Answer 18

Increase the reaction rate between the involved factors 250 000x

Question 19

Where is not tissue factor present under physiologic conditions?

Answer 19

Healthy endothelial cells

Blood

Question 20

How can tPA be increased?

Answer 20

In presence of a cofactor, which might be fibrin

Question 21

Primary thrombin inhibitor in blood? How is effect enhanced pharmacologically?

Answer 21

Antithrombin.

By the addition of heparin.

Question 22

List at least 3 triggers of platelet activation

Answer 22

Primary activators:
Collagen
Thrombin
Platelet-activating factor (PAF)
Secondary activators:
ADP
TXA2
Serotonin

Question 23

What initiates the blood coagulation at sites of injury?

Answer 23

Tissue factor with factor 7a

Question 24

What types of plasminogen activators are used in thrombolytic therapy?

Answer 24

1: tPA (Tissue type Plasminogen activators)
2: uPA (Urokinase Plasminogen activators)
3: Streptokinase

Question 25

How does Hirudin act?

Answer 25

Its a type of a “direct thrombin inhibitors”. Its an inhibitor of THROMBIN (direct without the need of a cofactor) by binding to exosite 1 and active site. Has a negatively charged tail, it binds to active site of thrombin and inactivates it. (it has a specific activity on fibrinogen) Hirudin prevent formation of blood clots & thrombus, do not interfere with ability of serum proteins.

Binds to both fibrin-bound and soluble thrombin

Question 26

1. Describe composition of prothrombinase complex

2. What are the structurally important elements of complex formation

Answer 26

1. composed by activated factor X and V

2. These factors are bound by Ca-ions to the negative phospholipid membrane

Question 27

What are the substrates for thrombin in blood coagulation system?

Answer 27

Fibrinogen (factor 2)
Factor 5, 8, 11, 13
PAR-receptor
Binds to thrombomodulin along with calcium to activate protein C.

Question 28

Enzymes that degrades fibrin clots?

Answer 28

Plasmin

Question 29

Role of Platelets

Answer 29

First, platelets stick to exposed collagen of the subendothelial layer: adhesion. Second, they change shape, turn on receptors and secrete chemical messengers (ADP, Vwf, thrombin, PDGF): activation. Third, they stick to each other: aggregation. Formation of this platelet plug (primary hemostasis) is followed by activation of the coagulation cascade with resultant fibrin deposition and linking (secondary hemostasis).

Question 30

Purpose of phospholipids on platelets membrane

Answer 30

Complex formaiton for tenase and prothrombinase complexes. This complexes enhance its activity 250 000x!

Phosphatidylserine with its negative charge can be used as a building block with Ca2+, cofactors, substrate and enzyme.

Question 31

Leiden mutation

Answer 31

Inherited disorder of blood clotting, activated protein C resistance. It results in a factor V variant that cannot be easily degraded by activated protein C.

Question 32

Effect of Coumarin (Warfarin); after how much time is the effect of coumarin observable?

Answer 32

a. Coumarin inhibits Vit K Epoxide Reductase which is responsible for Glu to Gla change of factors 2, 7, 9, 10
b. not an observable effect; it takes about a day to see the effects.

Question 33

Substrates of factor VII

Answer 33

Exposure of factor tissue factor (cofactor), which binds VIIa, causing activation of X -> Xa + through the alternative pathway, activation of factor 9

Question 34

How does endothelia cell initiate coagulation formation?

Answer 34

Damaged endothelium does not secrete the same amount of antithrombotic substances. Exposure of the extravascular matrix (E.g. Collagen and vWF) will cause platelet adherence and activaiton.

Question 35

What is the mechanism of action of heparin?

Answer 35

Heparin binds to exosite 2 on thrombin. This increase its affinity to antithrombin which leads to more thrombin removal.

Question 36

What is the role of the primary cilium of endothelial cells?

Answer 36

Shear stress -> Ca2+ -> NO production -> vasodilation

Question 37

Which component forms a secondary matrix in thrombi in addition ot fibrin?

Answer 37

Neutrophil extracellular trap (NET)

Question 38

Write down the targets of TFPI in the order of their binding

Answer 38

1: 10a
2: 7a with TF (in complex)

Question 39

List the three major targets of thrombin in the positive feed-back loops in blood plasma

Answer 39

5, 8, 11

Question 40

Function of alpha1-protease inhibitor (alpha1-antitrypsin)

Answer 40

Inactivated almost all serine proteases (e.g. thrombin and plasmin. Equimolar complexes.