Session 7: Regulation of Protein Activity

Question 1

Certain enzymes have an inactive protein precursor known as a ___

Answer 1

zymogen

Question 2

Zymogens can be activated by ___

Answer 2

proteolytic cleavage

Question 3

Proteolytic cleavage

Answer 3

the activation of a protein by a one-time, irreversible removal of part of the polypeptide chain

Question 4

An example of an enzyme that is produced as a zymogen

Answer 4

Protease

Question 5

Many ___ enzymes are synthesised as zymogens

Answer 5

digestive

Question 6

An example of a cascade mechanism involving proteolytic activation of enzymes

Answer 6

Blood clotting cascade is mediated by multiple proteolytic activations

Question 7

Three examples of proteolytic cleavage as a means of regulating enzyme activity in the cell

Answer 7

1) Activation of digestive enzymes = from zymogens (inactive precursors) to active form in stomach/pancreas e.g., pepsinogen zymogen is cleaved to active form of pepsin in stomach

2) Activation of hormones = insulin is synthesised as preproinsulin, cleaved to proinsulin and finally to active insulin

3) Deactivation of hormones = incretins in the blood

Question 8

Programmed cell death (apoptosis) is mediated by proteolytic ___ enzymes which are synthesised in their inactive (___) form.

Answer 8

Programmed cell death (apoptosis) is mediated by proteolytic caspase enzymes which are synthesised in their inactive procaspase form

Question 9

Trypsinogen is activated by ___

Answer 9

enteropeptidase and trypsin

Question 10

Enteropeptidase (master regulator) converts trypsinogen to ___.

Answer 10

trypsin

Question 11

Enterokinase can be found in the…

Answer 11

brush border (microvilli)

Question 12

Inappropriate activation of trypsin’s in pancreas can lead to pancreatic acinar damage (pancreatitis).

Secondary complication of pancreatitis

Answer 12

Acute respiratory distress syndrome

This is inflammation within the pancreas which has spread to other organs (e.g., lungs), causing protein dysregulation due to proteolytic cleavage.
It is seen as widespread opacities in the lungs

Question 13

Incretins

Answer 13

group of hormones that decrease blood glucose levels after eating. They mediate this by enhancing insulin release and inhibiting glucagon from pancreas

Question 14

Incretin examples - released after eating

Answer 14

GIP and GLP-1

Question 15

Incretins require ___ cleavage for activation and inactivation

Answer 15

proteolytic

Question 16

Which enzyme inactivates GLP-1 (incretin)?

Answer 16

Dipeptidyl peptidase-4 (DDP-IV)

Question 17

An adult has approximately ___ litres of blood

Answer 17

5-6

Question 18

An adult can usually withstand loss of ___ litre of blood without harmful effects

Answer 18

0.5

Question 19

Loss of ___ litre(s) of blood may cause hypovolemic shock in an adult

Answer 19

1

Question 20

The ___ pathway is a cascade of events that leads to haemostasis

Answer 20

coagulation

Question 21

What does the coagulation pathway achieve?

Answer 21

• Rapid healing
• Prevention of spontaneous bleeding

Question 22

What are the three steps to hemostasis (blood clotting process)

Answer 22

1) Vascular spasm
2) Platelet plug formation
3) Blood clotting (coagulation cascade)

Question 23

What occurs during the three steps of hemostasis (blood clotting process)

Answer 23

1) Vascular spasm
Smooth muscle contracts leading to vasoconstriction

2) Platelet plug formation
Injury to lining of vessel exposes collagen fibers. Platelets adhere and release chemicals that make nearby platelets sticky - lead to platelet plug formation

3) Blood clotting
Fibrin forms a mesh - this mesh traps red blood cells and platelets forming a clot

Question 24

What occurs during vascular spasm (step 1) of hemostasis (blood clotting process)

Answer 24

Smooth muscle contracts
Vasoconstriction

Question 25

What occurs during platelet plug formation (step 2) of hemostasis (blood clotting process)

Answer 25

Injury to vessel lining exposes collagen fibres Platelets adhere Platelets release chemicals that make nearby platelets sticky Platelet plug is formed

Question 26

What occurs during blood clotting (step 3) of hemostasis (blood clotting process)

Answer 26

Fibrin forms a mesh Mesh traps RBC and platelets, forming a CLOT

Question 27

Injury to a blood vessel, activates ___

Answer 27

platelets

Question 28

Clotting factors are ___ or ___ needed to activate the next step

Answer 28

proteases, cofactors

Question 29

Enzyme cascade

Answer 29

a molecular pathway in which the product of each reaction catalyzes the subsequent reaction (when enzymes activate enzymes)

Question 30

Example of an enzyme cascade pathway

Answer 30

The coagulation pathway

Question 31

The proteolytic cleavage of ___ forms fibrin and aggregation of fibrin forms ___

Answer 31

The proteolytic cleavage of fibrinogen forms fibrin and **aggregation of fibrin forms clots**

Question 32

Clot formation is highly controlled. It can be reversed by proteolytic cleavage of ___ by the enzyme ___

Answer 32

Clot formation is **highly controlled**. It can be **reversed** by **proteolytic cleavage of fibrin** by the enzyme **plasmin**

Question 33

The blood clotting cascade can be divided into the ___ pathway and the ___ pathway

Answer 33

Intrinsic, extrinsic

Question 34

There are ___ factors involved in the blood coagulation pathway

Answer 34

12

Question 35

The intrinsic pathway of the coagulation cascade can also be called the...

Answer 35

Contact activation pathway

Question 36

The intrinsic pathway (contact activation pathway) is activated by what?

Answer 36

**Trauma within the vascular system**

Question 37

What clotting factors in the intrinsic pathway are targeted to membrane by Gla domains?

Answer 37

**Factor IX (9) **and **Factor X (10)** are targeted to the membrane by Gla domains

Question 38

In the intrinsic pathway...

Answer 38

___ binds to calcium ions via Gla residues Prothrombin

Question 39

The extrinsic pathway of blood coagulation is also known as...

Answer 39

Tissue factor pathway

Question 40

The extrinsic pathway (tissue factor pathway) is activated by what?

Answer 40

external trauma

Question 41

In the extrinsic pathway of coagulation...

Answer 41

**Membrane damage** **exposes** extracellular domain of **tissue factor _ III (3)**

Question 42

The common endpoint for both the intrinsic and extrinsic coagulation pathways is...

Answer 42

The **intrinsic pathway ** - Triggers Factor XII (**12**) The **extrinsic pathway ** - Triggers Cofactor III (**3**) - These pathways both share the **common endpoint** of activating Factor X (**10**) - Factor X (**10**) then triggers the **conversion of prothrombin → thrombin**. - Thrombin **triggers** the conversion of **fibrinogen → fibrin clot**

Question 43

Structure of fibrinogen

Answer 43

- 340 kDa protein - **2 sets of tripeptides** (alpha/beta/gamma) **joined at N-termini** by **disulphide bonds** - **4 globular domains** linked by **rods** - Crab shape with the globular regions being the 'claws' of the crab

Question 44

The formation of a soft fibrin clot

Answer 44

Fibrinogen → Fibrin (catalyzed by thrombin) 1) Thrombin **cleaves fibrinopeptides A and B** from the central globular domain of fibrinogen 2) **Globular domains at the C-terminal** of the beta- and gamma- chains **interact with exposed sequences at the N-terminal** - this forms a **fibrin mesh** or **soft clot**

Question 45

The formation of a hard fibrin clot

Answer 45

The soft clot is **stabilised** via **addition of covalent crosslink amide bonds** between **side chains of lysine and glutamine residues**.

Question 46

The soft fibrin clot is stabilised via the addition of covalent crosslink ___ bonds between side chains of lysine and ___ residues

Answer 46

The soft fibrin clot is stabilised via the addition of covalent crosslink amide bonds between side chains of lysine and glutamine residues

Question 47

What enzyme catalyses the cross-linkage process in the conversion of a soft fibrin clot to a hard one?

Answer 47

Transglutaminase

Question 48

How is the clotting process stopped naturally in the body

Answer 48

1) **Dilution of clotting factors** by the blood and **removal by the liver**

Question 49

Specific inhibitors of clotting process

Answer 49

Anti-thrombin III (AT3)

Question 50

Name another way in which the clotting process can be stopped

Answer 50

Digestion by **proteases** e.g., FVa and VIIIa are degraded by **protein C**

Question 51

Tissue plasminogen activator (tPA)

Answer 51

a thrombolytic administered to some **patients** having a **heart attack** or stroke to **dissolve damaging blood clots**

Question 52

Streptokinase

Answer 52

thrombolytic medication which activates plasminogen - break down clots

Question 53

plasminogen to plasmin

Answer 53

Plasminogen is the precursor protein that is cleaved to form plasmin. Plasmin is the enzyme that degrades fibrin as a part of removing clots

Question 54

Clot removal

Answer 54

Fibrinolysis

Question 55

List some anticoagulants drugs

Answer 55

Heparin, Warfarin

Question 56

**Warfarin** (vitamin K antagonist) inhibits which four factors?

Answer 56

Factors **2, 7, 9 and 10** all depend on vitamin K

Question 57

Vitamin K antagonist anticoagulant

Answer 57

Warfarin

Question 58

What factors does Heparin anticoagulant inactivate and activate?

Answer 58

Heparin activates antithrombin III Heparin inactivates factors 2a and 10a

Question 59

Disorder of bleeding

Answer 59

Classic haemophilia

Question 60

Classic haemophilia results from a defect in factor ___

Answer 60

VIII (8)

Question 61

Reduced or absent factor VIII (8) results in reduced/absent ___ and prolonged ___

Answer 61

Reduced or absent factor VIII (8) results in reduced/absent clotting and prolonged bleeding (Classic Haemophilia = bleeding disorder)

Question 62

What enzyme facilitates fibrinolysis fibrin → fibrin fragments

Answer 62

Plasmin

Question 63

Inactive form (precursor) of plasmin enzyme which catalyzes fibrinolysis

Answer 63

Plasminogen

Question 64

Proteolytically active form of plasminogen

Answer 64

Plasmin enzymes

Question 65

Examples of clot-removing drugs which facilitate fibrinolysis (dissolve clots)

Answer 65

- Streptokinase - Tissue Plasminogen Activator (t-PA)

Question 66

The newer drug class of oral anticoagulant drugs inhibit which factors?

Answer 66

Inhibit class 2a, 10a

Question 67

Treatment for classic haemophilia?

Answer 67

Recombinant Factor VIII (8)