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ESA1 - Molecules, Genes And Disease > Regulation Of Protein Activity > Flashcards

Regulation Of Protein Activity Flashcards

1
Q

How could you control the regulation of proteins in the long term?

A
  • Change rate of protein synthesis

- Change rate of protein degradation

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2
Q

Define an ISOENZYME and give an example of these

A
  • Different forms of the same enzyme which have different kinetic properties (Km values)
  • e.g. Hexokinase (low Km for glucose) and Glucokinase (high Km for glucose, so is only active when conc of glucose in blood in high)
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3
Q

What is meant by product inhibition? Give an example of where this occurs.

A
  • Accumulation of the product of an enzyme controlled reaction inhibits the forward reaction
  • e.g. PFK is inhibited by high levels of Fructose-1,6-bisphosphate
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4
Q

What kind of graph would you expect for a protein that is allosterically regulated?

A

SIGMOIDAL relationship between [S] and rate of reaction v

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5
Q

Explain why allosterically regulated proteins show a sigmoidal relationship

A
  • Allosterically regulated protein usually have multiple subunits e.g. Haemoglobin
  • Substrate binding to one subunit is difficult at first but promotes the subsequent binding of substrate to other subunits (subsequent binding is progressively easier)
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6
Q

What is the effect of an allosteric activator?

A
  • Increase the proportion of enzymes in the high affinity R state
  • Curve shifts to the LEFT
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7
Q

How does an allosteric inhibitor affect the rate of reaction?

A
  • Decreases rate of reaction
  • Binds somewhere other than active site and promotes stabilisation of the low affinity T state
  • Curve shifts to the RIGHT
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8
Q

Why is Km insignificant when allosteric regulation is involved?

A
  • Km is used for hyperbolic relationships

- Allosteric regulation shows a sigmoidal relationship

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9
Q

Name 2 substances which act as allosteric activators for PFK

A
  • AMP

- Fructose-6-phosphate

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10
Q

Give an example of a covalent modification mechanism for modifying proteins

A
  • POST-TRANSLATIONAL PHOSPHORYLATION
  • Proteins phosphorylated using KINASE enzymes
  • Proteins dephosphorylated using PHOSPHATASE enzymes
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11
Q

Which 3 amino acid residues can be phosphorylated and why?

A
  • Serine
  • Threonine
  • Tyrosine
  • All contain -OH groups on their side chains which can accept terminal Pi from ATP
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12
Q

What type of bond is formed during phosphorylation?

A

COVALENT

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13
Q

How does a phosphatase enzyme work?

A
  • DEPHOSPHORYLATION
  • Catalyses the hydrolytic removal of phosphoryl groups from proteins
  • Uses water to break the covalent bond
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14
Q

Explain what is meant by ‘amplification’ of a signal and how this causes an enzyme cascade

A
  • Binding of receptor (signal) activates an enzyme (induces a kinase to phosphorylate)
  • Activated enzyme goes on to further activate other enzymes
  • Number of activated enzymes increases geometrically until there are thousands
  • One signal can activate thousands of enzymes in a few seconds due to AMPLIFICATION of the signal
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15
Q

Name 3 proteins which are activated by proteolytic cleavage

A
  • Pepsin
  • Trypsin
  • Insulin
  • Thrombin
  • Fibrin
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16
Q

What is a zymogen?

A

Inactive precursor of a protein

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17
Q

What is the significance of the activation of trypsin in the pancreas?

A
  • Enteropeptidase enzyme in pancreas activates trypsin by proteolytic cleavage of trypsinogen
  • Trypsin then activates subsequent pancreatic proteases by stimulating the proteolytic cleavage of each
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18
Q

How is protease activity regulated?

A
  • ENDOGENEOUS INHIBITORS
  • Once a zymogen is activated it cannot be switched off
  • Highly specific inhibitors are released which bind to active enzymes and inhibit their activity
19
Q

Give examples of reversible and irreversible mechanisms of protein regulation

A
  • REVERSIBLE - phosphorylation

- IRREVERSIBLE - proteolytic cleavage

20
Q

Name 4 ways in which proteins can be regulated in the short term

A
  • Substrate and product concentrations (feedback inhibition)

- Change in enzyme conformation by allosteric regulation, covalent modification or proteolytic cleavage

21
Q

What mechanism of damage might activate the intrinsic pathway of the blood clotting cascade?

A

Damaged endothelial lining of blood vessels

22
Q

What do both the intrinsic and extrinsic pathways have in common?

A

Both lead to activation of Factor X

23
Q

What is an ENDOPEPTIDASE?

A

Enzyme that breaks peptide bonds in specific places

24
Q

Explain how clots are localised to the site of damage

A
  • Damage to endothelial phospholipid bilayer attracts positively charged Ca2+ (Factor IV)
  • Calcium bridge is formed (highly positive)
  • Attracts highly negative Gla domains on Factors II, VII, IX and X tot he site of damage
  • Prothrombin (Factor II) binds to Ca2+ and will only be activated at the site if damage
25
How are Gla domains formed?
- Post translational modification of Glu residues on Factors II, VII, IX and X - Addition of COOH forms γ-carboxyglutamate which are highly NEGATIVE - Requires vitamin K
26
Which factors are activated in the intrinsic pathway?
- Factor XI - Factor IX - Activation of co-Factor XIII - FACTOR X
27
What factors are activated in the extrinsic pathway?
- Tissue Factor III - Factor VII - FACTOR X
28
Which factor(s) are involved in the activation of Prothrombin->Thrombin?
Factor X and co-Factor V
29
What is the role of Factor XIII?
- Transglutaminase | - Cross linking of FIBRIN by linkage of Glutamate and Lysine residues
30
What is cleaved from prothrombin to activate it to thrombin?
- Gla domain | - 2 Kringle domains
31
How does Tissue Factor II activate Factor VII?
- Membrane damage exposes extracellular domain of Tissue Factor III - AUTOCATALYTIC activation of Factor VII
32
How is polymerisation of fibrinogen prevented when inactive?
NEGATIVE N terminal regions cause fibrinogen molecules to REPEL EACHOTHER
33
Why is the globular domain of fibrinogen highly negative?
α, β and γ domains linked at N termini by DISULPHIDE BONDS
34
Describe the formation of a soft clot
- Activation of Thrombin via cascade mechanism - Thrombin cleaves fibrinopeptides A and B from the central globular domain, forming active FIBRIN - C terminal of the γ and β globular domains (-ve) are attracted to the N termini of the cleaved α and β chains (+ve) forming a fibrin mesh or soft clot
35
Describe how a fibrin clot is formed from a fibrin mesh (soft clot)
- Crosslinking between N termini of Glutamine and Lysine residues - Formation of AMIDE bonds by Factor XIII TRANSGLUTAMINASE which is activated by Thrombin
36
Why is the blood clotting cascade described as an example of positive feedback?
- Activation of Thrombin through the cascade of activation of previous Factors and co-Factors - Thrombin can go back through the cascade and activate previous clotting Factors XIII, XI, VIII and V - This increases the number of active clotting Factors which then increases the amount of active Thrombin
37
What is protein C?
- Protease enzyme involved in stopping the clotting process - Activated by thrombin binding to specific receptor THROMBOMODULIN - Degrades active co-Factors Va and VIIIa
38
What factor is deficient in Haemophilia A (classic)?
Factor VIII
39
Describe the methods in which the clotting process can be stopped
- Dilution of clotting factors by blood flow and removal by liver - Digestion of co-Factors V and VIII by protein C - Inhibition of thrombin by Antithrombin III
40
Describe the structure of fibrinogen
- CRAB - 2 sets of tripeptides containing α, β, γ chains - Linked at N termini by DISULPHIDE BONDS - 3 globular domains (C termini) linked by rods
41
How is haemophilia A treated?
Recombinant Factor VIII
42
What is plasmin and how is it activated?
- Serine ENDOPEPTIDASE that is involved in the degradation and breakdown of fibrin clots - Inactive zymogen PLASMINOGEN activated by tissue-plasmin activator t-PA - Also activated by Streptokinase (drug used to breakdown clots in coronary arteries)
43
Which clotting factors have Gla domains?
- Factor II (Thrombin) - Factor XI - Factor VII - Factor X
44
What vitamin is essential for clotting?
Vitamin K

ESA1 - Molecules, Genes And Disease (16 decks)

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