MCBG - Regulation Of Protein Function Flashcards
What are the effects of short term regulation of enzyme activity?
Change in substrate and product concentration, change in enzyme conformation
What are some effects of long term regulation of enzymes?
Change in rate of protein synthesis/degradation
What are isoenzymes?
Different forms of the same enzyme which have different kinetic properties.
What is product inhibition?
This occurs when accumulation of the product of a reaction inhibits the forward reaction.
What is the shape of the curve in a graph of reaction rate against substrate concentration for an allosteric enzyme?
Sigmoid
What are the two states that allosteric enzymes can exist in?
T state (low affinity) and R state (high affinity).
What do allosteric activators do in terms of T and R states?
They increase the proportion of enzyme in the R state.
What do allosteric inhibitors do in terms of T and R states?
They increase the proportion of enzyme in the T state.
Are ATP, citrate and H+ inhibitors or activators of phophofructokinase?
Inhibitors. AMP and fructose-2,6-bisphosphate are activators.
What do protein kinases do?
Transfer phosphate from ATP to the -OH group of ser, thr and tyr. This is “covalent modification”.
What do protein phosphatases do?
Reverse effects of kinases by catalysing hydrolytic removal of phosphoryl groups from proteins.
Give some reasons why a molecule might be phosphorylated.
- adds two negative charges
- phosphoryl groups can make H-bonds (useful)
- rate of phosphorylation (or dephosphorylation) can be adjusted
- allow for application affects
- link energy status of cell to metabolism through ATP
What is specific proteolytic cleavage?
A means of activating enzymes in biological systems, eg digestive enzymes are synthesised as zymogens.
What does pancreatic trypsin inhibitor do?
Binds to trypsin and stops it from activating other enzymes.
Which disorder is characterised by deficiency of alpha 1 antitrypsin and destruction of alveolar walls by elastase?
Emphysema
What are the two pathways of blood clotting?
Intrinsic and extrinsic. They both lead to factor 10 activation.
Briefly outline the blood clotting cascade.
Intrinsic/extrinsic pathways lead to factor X activation. This leads to thrombin activation, which leads to formation of a fibrin clot.
What is the benefit of blood clotting being a “cascade”?
It allows formation of a clot from activation of very small amounts of initial factor.
Is Ca2+ involved in the intrinsic pathway?
Yes.
Why does prothrombin contain two “Kringle” domains?
To ensure that it stays inactive.
What is the role of gamma-carboxyglutamate residues?
Post-translational modification of some factors in liver, addition of COOH groups to glutamate residues, allows interaction with sites of damage and brings together clotting factors.
How does prothrombin bind calcium ions?
Via gla residues
Roughly outline formation of a fibrin clot.
- Thrombin cleaves fibrinopeptides A and B from central globular domain
- globular domains at C-terminals of b and g chains interact with exposed N-termini of cleaved b and a chains to form clot
How is the clotting process stopped?
Prothrombin is diluted and removed by liver, factors are digested by proteases, specific inhibitors
Give a disease where the clotting process is inhibited.
Haemophilia
Define “zymogen”.
Inactive substance which is converted into an enzyme when activated by another enzyme
