Regulation Of Protein Function Flashcards
Protein function can be regulated in which 2 main ways?
Through gene expression
Through directly affecting the protein (e.g. Phosphorylation)
What are different short term ways of regulating protein function?
Changing enzyme and product concentration
Changing enzyme conformation - e.g allosteric regulation, covalent modification, proteolytic cleavage
What are different long term ways of regulating protein function?
Affecting gene expression - change in rate of protein synthesis
Change in the rate of protein degradation - ubiquitin-proteasome pathway
What are isoenzymes?
Different forms of the same enzymes with different kinetic properties
What is product inhibition?
Where accumulation of the product formed in a reaction inhibits the forward reaction
Allosterically regulated proteins (enzymes) show which sort of curve?
Sigmoidal curve
What sort of proteins are allosterically regulated?
Multi-subunit proteins and enzymes
Where do allosteric activators/inhibitors bind to an enzyme?
At the allosteric site - away from the active site
What does an allosteric activator do?
Increase the proportion of the enzyme in the R state
What does an allosteric inhibitor do?
Increase the proportion of the enzyme in the T state
What does phosphofructokinase do? (PFK)
Sets the pace for glycolysis
How is phosphofructokinase regulated?
Allosterically regulated
Activators = cyclic AMP, fructose-2,6-bisphosphate Inhibitors = ATP, citrate, H+ ions
What is the most common type of covalent modification of a protein?
Phosphorylation
Phosphorylation of proteins to regulate their function is carried out by which enzymes?
Protein kinases
How do protein kinases work to phosphorylate a protein?
Transfer the terminal phosphate from ATP to the OH group of certain amino acid residues
What enzymes work to reverse the effect of protein kinases?
Protein phosphatases
What does phosphorylation do to a protein?
Adds 2 negative charges
Allows hydrogen bonds to be made
Is proteolytic cleavage reversible or irreversible?
Irreversible
Digestive enzymes are synthesised as ________
Zymogens
What are zymogens?
An inactive precursor of an enzyme
Apoptosis is mediated by which enzymes? How are they synthesised?
Cascades
In procaspase form (zymogen)
By which two pathways can the blood clotting cascade be activated?
Intrinsic pathway
Extrinsic pathway
What is the intrinsic pathway of the blood clotting cascade?
Damaged endothelial lining of blood cells promotes binding of factor XII
What is the intrinsic pathway of the blood clotting cascade?
Trauma releases tissue factor (factor III)
What do both the intrinsic and extrinsic pathways of the blood clotting cascade result in?
Factor X activation
Thrombin activation (prothrombin —> thrombin)
Fibrin clot formation (fibrinogen —> fibrin clot)
What is the start of both the intrinsic and extrinsic pathways of the blood clotting cascade?
Both start with membrane damage
What is the function of Gla domains?
Directs proteins to the damaged membrane in the blood clotting cascade
What makes up the structure of a prothrombin molecule?
Gla domain at n-terminus Two kringle domains keeping prothrombin inactive Two cleavage sites Serine protease (active thrombin part)
Where are Gla domains added on to blood clotting factors?
As a modification in the liver
How do Gla domains direct factors to sites of membrane damage?
Highly -ve —> due to glutamate residues + COOH groups
Forms bridges with +ve calcium ions at sites of damage
What is the structure of fibrinogen?
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
How does thrombin interact with fibrinogen?
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
How is a soft clot stabilised to form a fibrin clot?
Further cross linking occurs using the enzyme - transglutaminase
Classic haemophilia is a defect in which factor?
Factor 8
Is an allosteric activator for factor 9
How is the blood clotting process stopped? (3)
Dilution of clotting factors by blood flow and removal by the liver
Digestion of certain factors by proteases
Specific inhibitors (e.g. Heparin)
How are fibrin clots broken down?
Fibrinolysis
The enzyme plasmin breaks down the fibrin clots into fibrin fragments
What is warfarin?
An anti-coagulant
Blood thinning medication
