Biochem 43 Flashcards

A bleeding patient has impaired platelet attachment to exposed subendothelium despite a normal platelet count. Which protein is most directly deficient?

A. von Willebrand factor
B. Protein C cofactor
C. Antithrombin III
D. Tissue plasminogen activator

A deep vascular laceration exposes tissue factor to circulating blood. Which pair is ultimately generated downstream?

A. Plasmin and protein C
B. Fibrinogen and prekallikrein
C. Albumin and ceruloplasmin
D. Thrombin and factor XIII

Which pair of coagulation proteins primarily serves as binding proteins?

A. II and X
B. V and VIII
C. VII and IX
D. XI and XII

Most important serum protein?

A monoclonal spike on serum electrophoresis reflects proliferation of which immunoglobulin-secreting cell?

A. Plasma cell
B. Kupffer cell
C. Mast cell
D. Megakaryocyte

Failure of which plasma system most directly impairs clearance of circulating antigen-antibody complexes?

A. Kallikrein system
B. Complement system
C. Fibrinolytic system
D. Contact pathway

Which combination can activate complement in the way described here?

A. Heparin and platelet factor 4
B. Thrombin and fibrin monomers
C. Collagen and dense granules
D. Immune complexes and bacterial polysaccharides

The major serine protease inhibitor of human plasma is:

A. C1 esterase inhibitor
B. Alpha-2 macroglobulin
C. α1-antitrypsin
D. Tissue factor inhibitor

Which amino acid residue is necessary for α1-antitrypsin binding to proteases?

A. Methionine 358
B. Glycine 202
C. Lysine 72
D. Tyrosine 110

Markedly decreased hepatic secretion of α1-antitrypsin is most likely due to:

A. Promoter methylation
B. Intron 1 deletion
C. Frameshift in exon 2
D. Point mutation in exon 5

A patient develops antibodies against platelet glycoproteins with no discernible cause. Which diagnosis best fits?

A. Hemolytic uremic syndrome
B. Idiopathic thrombocytopenic purpura
C. Bernard-Soulier syndrome
D. Disseminated intravascular coagulation

Which substance is characteristically stored in platelet electron-dense granules?

A. Platelet-derived growth factor
B. von Willebrand factor
C. Serotonin
D. Hydrolytic enzymes

Which molecule is a classic constituent of platelet α-granules?

A. Fibrinogen
B. ATP
C. Calcium
D. Serotonin

Platelet lysosomal granules characteristically contain:

A. ADP and ATP
B. Fibrinogen and vWF
C. Calcium and serotonin
D. Hydrolytic enzymes

Which set lists the three fundamental platelet mechanisms in coagulation?

A. Activation, inhibition, lysis
B. Adhesion, aggregation, secretion
C. Binding, cleavage, diffusion
D. Vasoconstriction, repair, lysis

von Willebrand factor has two major jobs:

1. Helps platelets adhere to _____ endothelium.
2. Carries and protects factor _____ in the blood.

A patient lacking von Willebrand factor would rapidly clear which coagulation factor from plasma?

A. Factor V
B. Factor VII
C. Factor VIII
D. Factor XIII

When exposed subendothelial collagen binds platelet GPIa, what is the most immediate platelet response?

A. Change from disk to sphere
B. Formation of plasmin
C. Activation of complement
D. Cleavage of von Willebrand factor

Binding of subendothelial vWF to platelet GPIb most directly exposes binding sites for:

A. Collagen and thrombin
B. ADP and serotonin
C. Albumin and transferrin
D. Fibrinogen and vWF

GPIb = platelet adhesion to ______
GPIIb/IIIa = platelet aggregation via ______

An inherited mutation in platelet GPIb causes which disorder?

A. Glanzmann thrombasthenia
B. Bernard-Soulier syndrome
C. Idiopathic thrombocytopenia purpura
D. Thrombotic thrombocytopenic purpura

Familial TTP is most closely associated with mutation of which enzyme?

A. Platelet cyclooxygenase
B. Factor VIII cofactor
C. vWF-specific metalloprotease
D. Platelet fibrinogen receptor

ADP released from activated platelets most directly promotes further exposure of:

A. GPIIb/IIIa binding sites
B. Tissue factor molecules
C. Factor XIII cross-links
D. Lysosomal hydrolases

The α and β peptides of fibrinogen are held together primarily by:

A. Ionic interactions
B. Hydrogen bonds
C. Ester linkages
D. Disulfide bonds

A patient has an isolated defect in a coagulation enzyme class shared by factors VII, IX, X, XI, and prothrombin. Which class is affected?

A. Serine proteases
B. Calcium-binding cofactors
C. Fibrin cross-linkers
D. Platelet glycoproteins

Which pair functions primarily as cofactor binding proteins within the coagulation cascade?

A. II and X
B. VII and IX
C. XI and XIII
D. V and VIII

In response to collagen and thrombin, activated platelets release which prominent vasoconstrictor pair?

A. ADP and fibrinogen
B. Serotonin and thromboxane A2
C. vWF and PDGF
D. ATP and calcium

A patient forms unstable clots that fail to become covalently cross-linked. Which factor normally acts as a Ca2+-dependent transglutaminase?

A. Factor V
B. Factor VIII
C. Factor XIII
D. Factor XI

Which sequence best describes the key steps of the extrinsic pathway?

A. VII binds tissue factor, activates X
B. X binds collagen, activates IX
C. XI activates IX, then VIII
D. XII binds platelets, activates X

During fibrin stabilization, factor XIIIa catalyzes which reaction between fibrin monomers?

A. Hydrolysis of lysine-serine bonds
B. Oxidation of methionine residues
C. Transamidation of glutamine and lysine
D. Carboxylation of aspartate residues

Which activated coagulation factor is the only enzyme in the cascade that is not a serine protease?

A. Factor XIIIa
B. Factor Xa
C. Factor VIIa
D. Thrombin

A patient on a vitamin K antagonist will produce reduced amounts of which gamma-carboxylated factor set?

A. V, VIII, XI, XIII
B. I, V, VIII, XII
C. II, VII, IX, X
D. VIII, IX, XI, XII

Vitamin K adds γ-carboxyglutamate residues to certain clotting factors, allowing them to bind Ca²⁺ and attach to phospholipid surfaces. Which pair of clotting factors uses this mechanism?

A. Factor VII and IX
B. Factor X and prothrombin
C. Factor V and VIII
D. Factor XI and XIII

Warfarin most directly impairs gamma-carboxylation of which anticoagulant pair in addition to clotting factors?

A. Protein C and protein S
B. Antithrombin and heparin cofactor
C. Plasminogen and fibrinogen
D. Thrombomodulin and tissue factor

A mutation disrupts assembly of the prothrombinase complex by altering a cofactor that binds Xa and prothrombin. Which factor is affected?

A. Factor VIIIa
B. Factor XIIIa
C. Factor Va
D. Factor VIIa

Vitamin K is functionally active in which chemical form?

A. Quinone form
B. Hydroquinone form
C. Epoxide form
D. Aldehyde form

The enzyme targeted by warfarin is best identified as:

A. Vitamin K epoxide reductase
B. Gamma-glutamyl carboxylase
C. Tissue factor protease
D. Thrombomodulin reductase

Which group is activated by thrombin in its prothrombotic regulatory role?

A. II, VII, X
B. VIII, IX, XIII
C. V, VIII, XI
D. Protein C, protein S, XII

Which action directly promotes clot formation by thrombin?

A. Activating plasmin from plasminogen
B. Cleaving factor XIII to XIIIa
C. Inhibiting release of factor VIII
D. Destroying factors Va and VIIIa

Thrombin produces antithrombotic effects after binding to:

A. von Willebrand factor
B. Antithrombin III
C. Heparan sulfate
D. Thrombomodulin

Binding of thrombin to thrombomodulin leads to activation of which anticoagulant?

A. Protein S
B. Protein C
C. Factor V
D. Plasmin

A neonate with a homozygous defect dies early from severe thrombotic disease. Deficiency of which pair is most consistent with this presentation?

A. Factors V and VIII
B. Factors IX and X
C. Protein C and protein S
D. Antithrombin and fibrinogen

The activated protein C complex exerts anticoagulant effects by destroying which factors?

A. Va and VIIIa
B. VIIa and IXa
C. XIa and XIIIa
D. IIa and Xa

A patient with inherited thrombophilia has factor V Leiden. Which amino acid substitution is classically present?

A. Glycine to serine
B. Lysine to methionine
C. Tyrosine to cysteine
D. Arginine to glutamine

A young adult with inherited thrombophilia develops a postoperative leg clot. Which condition is most strongly associated with Factor V Leiden?

A. Deep venous thrombosis
B. Hemophilia A bleeding
C. Bernard-Soulier syndrome
D. Thrombotic thrombocytopenic purpura

Activity of thrombin is primarily restrained by which serpin?

A. Protein C
B. Antithrombin III
C. Alpha-2 antiplasmin
D. Tissue factor pathway inhibitor

Formation of the antithrombin III-thrombin complex involves which residue pair?

A. Serine on thrombin
B. Glutamine on thrombin
C. Lysine on thrombin
D. Tyrosine on thrombin

Formation of the antithrombin III-thrombin complex involves which residue pair? (second pair)

A. Lysine on antithrombin
B. Arginine on antithrombin
C. Histidine on antithrombin
D. Cysteine on antithrombin

Heparin accelerates antithrombin III activity by binding primarily to which residue on antithrombin III?

A. Lysine
B. Arginine
C. Serine
D. Glutamate

The antithrombin III-heparin complex can directly inactivate which factor?

A. Factor VIIa
B. Activated protein C
C. Factor VIIIa
D. Factor Xa

Healthy endothelial cells reduce platelet aggregation by synthesizing which pair?

A. TXA2 and serotonin
B. PGI2 and nitric oxide
C. ADP and thrombin
D. Fibrinogen and vWF

Which enzyme directly cleaves fibrin during fibrinolysis?

A. Plasmin
B. Thrombin
C. Kallikrein
D. Factor XIIIa

In addition to suppressing coagulation, activated protein C promotes fibrinolysis by stimulating release of:

A. Thrombomodulin
B. von Willebrand factor
C. Tissue plasminogen activator
D. Platelet factor 4

Circulating plasmin is rapidly neutralized by which inhibitor?

A. Alpha-1 antitrypsin
B. Alpha-2 antiplasmin
C. Antithrombin III
D. Protein S

A boy with hemarthroses has classic hemophilia A. Which factor is deficient?

A. Factor IX
B. Factor VIII
C. Factor XI
D. Factor XIII

A patient with hemophilia B most likely has a mutation in which factor?

A. Factor V
B. Factor VIII
C. Factor IX
D. Factor X

A point mutation R98W in VKORC1 is associated with which disorder?

A. Hemophilia B
B. Bernard-Soulier syndrome
C. Glanzmann thrombasthenia
D. VKCFD2

Clopidogrel and ticagrelor inhibit platelet aggregation by blocking which receptor?

A. GPIIb/IIIa receptor
B. PAR-1 receptor
C. P2Y12 receptor
D. GPIb receptor

A patient with severe hypoalbuminemia develops dependent edema despite normal cardiac function. Which plasma protein role is most directly impaired?

A. Maintaining plasma oncotic pressure
B. Cross-linking fibrin polymers
C. Activating platelet P2Y12 receptors
D. Cleaving fibrin during lysis

A patient with thrombocytopenia continues to ooze from a small vascular injury. Which normal platelet function is most immediately lost?

A. Mechanical plug formation
B. Fibrin monomer degradation
C. Vitamin K regeneration
D. Gamma-carboxylation of factors

Platelets become activated after binding to a site of vascular injury. What is the most important immediate consequence?

A. Reduced local vasoconstriction
B. Increased platelet aggregation
C. Decreased fibrinogen binding
D. Inhibition of thrombin formation

At the site of endothelial injury, circulating fibrinogen most directly binds to:

A. Resting erythrocyte membranes
B. Activated platelets
C. Soluble albumin complexes
D. Endothelial thrombomodulin

Normal hemostasis requires tight regulation of clotting primarily to prevent:

A. Polycythemia and leukopenia
B. Thrombosis and bleeding
C. Hypertension and bradycardia
D. Acidosis and hypoxemia

The clotting cascade is best described as a sequence of events leading to activation of:

A. Plasmin
B. Fibrinogen
C. Thrombin
D. Albumin

A patient has impaired conversion of fibrinogen into fibrin during clot formation. Which enzyme is most directly deficient?

A. Thrombin
B. Plasmin
C. Protein C
D. Antithrombin III

A newly formed soft clot fails to become a stable hard clot. Which thrombin-dependent process is most likely defective?

A. Platelet serotonin release
B. Fibrin cross-linking
C. Protein S degradation
D. Plasminogen activation

Proteins C and S act together to regulate coagulation after being activated by:

A. Fibrinogen
B. Heparin
C. Thrombin
D. Plasmin

Vitamin K–dependent clotting factors contain γ-carboxyglutamate residues. What do these residues allow the clotting factors to bind during coagulation?

A. Sodium and fibrin
B. Calcium and membranes
C. Albumin and collagen
D. Plasmin and heparin

Antithrombin III is best classified as which type of regulatory molecule?

A. Serine protease inhibitor
B. Platelet adhesion receptor
C. Vitamin K reductase
D. Fibrin cross-linking enzyme

Which protease is uniquely capable of dissolving an established fibrin clot?

A. Thrombin
B. Factor Xa
C. Plasmin
D. Factor XIIIa

A boy with recurrent hemarthrosis is missing an essential factor for thrombin activation. Which diagnosis best fits?

A. Hemophilia A
B. Bernard-Soulier syndrome
C. Factor V Leiden
D. Idiopathic thrombocytopenia purpura

Which complement protein can interact with bacterial cell polysaccharides to activate the complement system?

A. C1 esterase inhibitor

B. C3b

C. Factor XIII

D. Protein S

Which set correctly lists the major contents of platelet electron-dense granules?

A. PDGF, vWF, fibrinogen, serotonin

B. ADP, fibrinogen, calcium, PDGF

C. Calcium, ADP, ATP, serotonin

D. ATP, vWF, PDGF, hydrolases

Which group is found in platelet α-granules?

A. PDGF, fibrinogen, vWF, β-thromboglobulin

B. Calcium, ADP, ATP, serotonin

C. Hydrolytic enzymes

D. Thrombin, plasmin, protein C, ADP

Which sequence best describes the extrinsic coagulation pathway?

A. XIa activates IX, then X

B. XII activates XI, then IX

C. Xa binds tissue factor, activating VII

D. VII binds tissue factor, then VIIa activates X

Vitamin K epoxide reductase helps regenerate vitamin K toward which form?

A. Quinone

B. Fibrinogen

C. Hydroxylated form

D. Gamma-carboxylate

Which action of thrombin promotes factor VIII activity during coagulation?

A. Degrading factor VIIIa

B. Binding factor VIII to fibrin

C. Releasing factor VIII from vWF

D. Converting factor VIII to plasmin

Deficiency of functional protein C or protein S most strongly increases the risk of which condition?

A. Hemophilia B

B. Bernard-Soulier syndrome

C. Immune thrombocytopenia

D. Venous thromboembolism

Which pair is not inactivated by the antithrombin III-heparin complex?

A. IXa and Xa

B. VIIa and activated protein C

C. XIa and Xa

D. IXa and XIa

Activated protein C can reduce platelet aggregation by stimulating secretion of which compound?

A. PGI2

B. Thromboxane A2

C. Serotonin

D. Fibrinogen