Session 3 -- Protein Regulation Flashcards
What are the short term methods of maintaining enzyme activity?
- Concentrations of product and substrate
2. Changes in enzyme conformation
Give examples of regulation by changes in enzyme conformation
- Allosteric regulation
- Covalent Modification
- Proteolytic Cleavage
Give the two main long term methods of maintaining enzyme activity
Rate of protein synthesis
Rate of protein degradation
Describe allosteric regulation
Enzymes have multiple active sites
Binding of one substrate enhances substrate binding to other sites
Activators increase activity by converting T to R state
Inhibitors decrease activity by converting R to T state
What type of curves to allosteric enzymes show?
Sigmoidal curve
Give an example of an allosteric enzyme
Phosphofructokinase – sets the pace of glycolysis
Activated by AMP and fructose - 2,6 -bisphosphate
Inhibited by ATP, citrate and H+
Describe covalent modification
The addition of a group to proteins via amino acids
Give the main example of covalent modification
Phosphorylation – the addition of a phosphate group to -OH groups, converting ATP to ADP
What are the enzymes which catalysed the attachment and removal of phosphate groups?
Kinases catalyse attachment of phosphate groups
Phosphatases catalyse the removal of phosphate groups
Describe proteolytic activation
Zymogens are activated by the removal of part of the polypeptide chain in order to transport enzymes to their site of action without causing damage on the way (proteases)
How is the rate of protein synthesis controlled?
By changing the rate of mRNA transcription
How is the rate of protein degradation controlled?
Proteins can be tagged for destruction by the addition of ubiquitin, a small protein molecule
What are the main ways in which metabolic pathways are controlled?
Feedback inhibition
Feedforward activation
Counter regulation of pathways
What is the intrinsic pathway for blood clotting?
Damaged endothelial lining of blood cells promotes the binding of factors 9 and 11 which are targeted to membrane by Gla domains. This pathway maintains the thrombin activation.
What is the extrinsic pathway for blood clotting?
Vascular damage releases factor 3 which leads to the activation of factor 7, activating factor 10 …
Describe the structure of prothrombin
Thrombin part is contained in C-terminal domain
Two kringle domains maintain the inactivated form
Gla domains allow for the targeting of the enzyme to its site of action
What are Gla residues and why are they important?
Are additions of COOH groups to glutamate residues forming carboxyglutamate (Gla). Occurs by post-translational modification in the liver.
Allows for the interaction with sites of damage, bringing together clotting factors
What is fibrinogen and describe its structure
Inactive zymogen, has highly negative charges on ends to prevent aggregation of fibrinogen. Made up of 2 sets of tripeptides joined by disulphide bonds
How is fibrin converted to fibrinogen?
Thrombin cleaves A and B fibrinopeptides, allowing globular domains to interact with exposed sequences forming a fibrin mesh. The mesh is stabilised by amide bonds formed between different monomers, catalysed by transglutaminase (activated by thrombin by protransglutaminase)
What occurs in haemophilia?
A defect occurs in factor 8 which stimulates the activity of factor 9 by positive feedback and amplifying the clotting signal. Treatment is with a recombinant factor 8.
How is the clotting process terminated?
- Clotting factor are diluted by blood flow and removal by the liver
- Digestion of clot by proteases (t-PA and streptokinase)
- Binding by inhibitor molecules (antithrombin 3)
What are the main regulation methods for the blood clotting cascade?
- Inactive zymogens are present at low concentrations
- The initial signal is amplified
- Gla domains limit activation to site of damage
- Thrombin activates multiple factors
- Termination by numerous processes
