Regulation of Protein Function Flashcards
How are enzymes regulated in the short term?
Substrate and product concentration
Change in enzyme conformation- allosteric regulation, covalent modification or proteolytic cleavage
How are enzymes regulated in the long term?
Change in rate of protein synthesis
or change in rate of protein degradation
What is an Isoenzyme?
Different forms of the same enzyme that have different kinetic properties
What is product inhibition?
Accumulation of the product of a reaction inhibits the forward reaction
What are allosteric enzymes?
Show a sigmoidal relationship between rate and substrate concentration
Why do allosteric enzymes have a sigmoidal shape?
Multi subunit so have two different conformations
T state- low affinity
R state- high affinity
What are allosteric activators?
Increase proportion of enzyme in the R state
What are allosteric inhibitors?
Increase the proportion of enzyme in the T state
What does phosphofructokinase do?
allosterically regulated and sets pace of glycolysis
What does Protein kInases do?
Transfer the terminal phosphate from ATP to the OH group of Ser, Thr or Tyr
What do Protein phosphatases do?
Reverse the effects of kinases by catalysing the hydrolytic removal of phosphoryl groups from proteins
Why are Protein phosphatates so effective?
Adds 2 negative charges
Phosphor group can make H bonds
Rate of phosphorylation/ dephosphorylation on can be adjusted
amplification effects
Links energy status of cell to metabolism through ATP
What is amplification by enzyme cascades?
When an enzyme activated enzymes the number of affected molecules increased geometrically
What are Zymogens?
inactive precursors
What is an Endogenous inhibitor
binds to protein and stops activity
How does a chain in rate of protein synthesis occur?
Enzyme induction or repression
How does a change in rate of protein degradation occur?
Ubiquitin-proteasome pathway
What is the intrinsic pathway of the blood clotting cascade?
Damaged endothelial lining of the blood cells promote binding of fact XII
What is the extrinsic pathway of the blood clotting cascade?
Trauma released tissue factor III
Why is factor X important?
Common end point for both pathways
causes thrombin activation
What does Thrombin activation cause?
Formation of Fibrin clot
What is the molecular prothrombin?
Protease function is contained in the C-terminus domain
Two kringle domains keep prothrombin in the inactive form
Gla domains target it to appropriate sites for activation
What is the role of Gla residues?
Allows integration with sites of damage and brings together clotting factors
What is calciums role with prothrombin?
Calcium binds at Gla residues so only prothrombin next to site of damage will be activated- localised
What is the structure of Fibrinogen?
2 sets of tripeptides with alpha, gamma and beta joined at the N terminus by disulphide bonds
3 globular domains linked by rods
alpha and beta- negative at n terminus to prevent aggregation
How is a fibrin clot formed?
- Thrombin cleaves fibrinopeptides A and B from the central globular domain of fibrinogen
- Globular remains at the end of the C terminus ends of the B and G chains interact with exposed sequences at the N terminus of the cleaves A and B chains to from fibrin mesh
- amide bonds form between side chains of Lysine and Glutamine
- Transglutaminase catalyses the cross linking which is activated by protransgultaminase by Thrombin
What causes Haemophilia?
defect in factor VIII
Accelerated clot formation
How is the clotting process stopped?
- Localisation of prothrombin- dilute clotting factors by blood flow and removal by liver
- digestion by proteases
- specific inhibitors e.g. AT3
What is Fibrinolysis?
The enzymatic breakdown of the fibrin in blood clots
What are the key control points in blood clotting?
- Inactive zymogens at low concentration
- proteolytic activation
- amplification by cascade mechanism
- Clustering of clotting factors a site of damage
- feedback activation by thrombin- continuation of clotting
- termination by multiple mechanisms
- Clot breakdown controlled by proteolytic activation
What forms a clot?
Aggregation of Fibrin
What does plasmin do?
proteolytic cleavage of Fibrin- reverses clot formation
