Regulation Of Protein Function

Question 1

Protein function can be regulated in which 2 main ways?

Answer 1

Through gene expression

Through directly affecting the protein (e.g. Phosphorylation)

Question 2

What are different short term ways of regulating protein function?

Answer 2

Changing enzyme and product concentration

Changing enzyme conformation - e.g allosteric regulation, covalent modification, proteolytic cleavage

Question 3

What are different long term ways of regulating protein function?

Answer 3

Affecting gene expression - change in rate of protein synthesis

Change in the rate of protein degradation - ubiquitin-proteasome pathway

Question 4

What are isoenzymes?

Answer 4

Different forms of the same enzymes with different kinetic properties

Question 5

What is product inhibition?

Answer 5

Where accumulation of the product formed in a reaction inhibits the forward reaction

Question 6

Allosterically regulated proteins (enzymes) show which sort of curve?

Answer 6

Sigmoidal curve

Question 7

What sort of proteins are allosterically regulated?

Answer 7

Multi-subunit proteins and enzymes

Question 8

Where do allosteric activators/inhibitors bind to an enzyme?

Answer 8

At the allosteric site - away from the active site

Question 9

What does an allosteric activator do?

Answer 9

Increase the proportion of the enzyme in the R state

Question 10

What does an allosteric inhibitor do?

Answer 10

Increase the proportion of the enzyme in the T state

Question 11

What does phosphofructokinase do? (PFK)

Answer 11

Sets the pace for glycolysis

Question 12

How is phosphofructokinase regulated?

Answer 12

Allosterically regulated

Activators = cyclic AMP, fructose-2,6-bisphosphate
Inhibitors = ATP, citrate, H+ ions

Question 13

What is the most common type of covalent modification of a protein?

Answer 13

Phosphorylation

Question 14

Phosphorylation of proteins to regulate their function is carried out by which enzymes?

Answer 14

Protein kinases

Question 15

How do protein kinases work to phosphorylate a protein?

Answer 15

Transfer the terminal phosphate from ATP to the OH group of certain amino acid residues

Question 16

What enzymes work to reverse the effect of protein kinases?

Answer 16

Protein phosphatases

Question 17

What does phosphorylation do to a protein?

Answer 17

Adds 2 negative charges

Allows hydrogen bonds to be made

Question 18

Is proteolytic cleavage reversible or irreversible?

Answer 18

Irreversible

Question 19

Digestive enzymes are synthesised as ________

Answer 19

Zymogens

Question 20

What are zymogens?

Answer 20

An inactive precursor of an enzyme

Question 21

Apoptosis is mediated by which enzymes? How are they synthesised?

Answer 21

Cascades

In procaspase form (zymogen)

Question 22

By which two pathways can the blood clotting cascade be activated?

Answer 22

Intrinsic pathway

Extrinsic pathway

Question 23

What is the intrinsic pathway of the blood clotting cascade?

Answer 23

Damaged endothelial lining of blood cells promotes binding of factor XII

Question 24

What is the intrinsic pathway of the blood clotting cascade?

Answer 24

Trauma releases tissue factor (factor III)

Question 25

What do both the intrinsic and extrinsic pathways of the blood clotting cascade result in?

Answer 25

Factor X activation
Thrombin activation (prothrombin —> thrombin)
Fibrin clot formation (fibrinogen —> fibrin clot)

Question 26

What is the start of both the intrinsic and extrinsic pathways of the blood clotting cascade?

Answer 26

Both start with membrane damage

Question 27

What is the function of Gla domains?

Answer 27

Directs proteins to the damaged membrane in the blood clotting cascade

Question 28

What makes up the structure of a prothrombin molecule?

Answer 28

Gla domain at n-terminus 
Two kringle domains keeping prothrombin inactive
Two cleavage sites
Serine protease (active thrombin part)

Question 29

Where are Gla domains added on to blood clotting factors?

Answer 29

As a modification in the liver

Question 30

How do Gla domains direct factors to sites of membrane damage?

Answer 30

Highly -ve —> due to glutamate residues + COOH groups

Forms bridges with +ve calcium ions at sites of damage

Question 31

What is the structure of fibrinogen?

Answer 31

Two sets of tripeptides joined at n-termini by disulphide bonds 3 globular domains linked by rods
N terminal of alpha and beta chains highly -ve charged preventing aggregation of fibrinogen

Question 32

How does thrombin interact with fibrinogen?

Answer 32

Thrombin cleaves fibrinopeptides at n terminal of alpha and beta chains
Globular domains at c terminals interact with exposed sequences at n terminals to form a soft clot

Question 33

How is a soft clot stabilised to form a fibrin clot?

Answer 33

Further cross linking occurs using the enzyme - transglutaminase

Question 34

Classic haemophilia is a defect in which factor?

Answer 34

Factor 8

Is an allosteric activator for factor 9

Question 35

How is the blood clotting process stopped? (3)

Answer 35

Dilution of clotting factors by blood flow and removal by the liver
Digestion of certain factors by proteases
Specific inhibitors (e.g. Heparin)

Question 36

How are fibrin clots broken down?

Answer 36

Fibrinolysis

The enzyme plasmin breaks down the fibrin clots into fibrin fragments

Question 37

What is warfarin?

Answer 37

An anti-coagulant

Blood thinning medication