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14 Cards in this Set
- Front
- Back
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What are the components of a G-Protein? |
3 subunits: alpha subunit beta subunit gamma subunit |
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How do the subunits of a G protein interact? |
Beta and gamma subunits will interact together and do not come apart. This subunit component will interact with the alpha subunit which often comes apart. The formation of the the three is an alpha,beta,gamma heterotrimer |
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There are different families of G-Protein which depend on the function of the activated G-Protein. 1. What is the basis of the differing functions? 2. What are the names of each family and what different functions do they have? |
1. The differing functions are usually based on the activity of the alpha subunit. 2. a) G-alpha (Ga) s - stimulates adenylate cyclase b) GA i - Inhibits adenylate cyclase c) GA t - stimulates cGMP phosphodiesterase d) GA q - Increases IP3 and intracellular calcium e) GA 13 - Stimulates Na+ and H+ exchange |
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What are main initiators of each G protein family? |
GAs : Beta adrenergic amines, glucagon, parathyroid hormone + Many others GAi: Acetylcholine, alpha adrenergic amines + many neurotransmitters GAt: Photons GAq: Acetylcholine, alpha adrenergic amines + many neurotransmitters GA13: Thrombin and other agonists |
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What is the process of action of a heterotrimeric G protein? |
The alpha subunit is part of a molecular time switch - when GDP is bound the time switch is inactive when GTP is bound the time switch is active. 1. When an activation signal reaches a G protein linked receptor, the receptor undergoes a conformational change allowing the G protein's alpha subunit to bind to the receptor. 2. When the alpha subunit binds a further conformational change occurs which releases GDP from the alpha subunit 3. The conformational change allows the binding of GTP to the alpha subunit. 4. GTP binding causes dissociation of the alpha subunit from the heterotrimer 5. The dissociated alpha subunit is able to interact with a membrane bound effector protein - causing an effect (e.g. Activation of Adenylate Cyclase.) 6. The GTP in the alpha subunit is hydrolysed resulting in the formation of GDP. 7. Alpha subunit returns to the BetaGamma heterodimer to reform the full G-Protein. |
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How is the activation period of the alpha subunit controlled? |
GTP is hydrolysed very slowly which allows a greater period of activation time. |
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How can a single receptor activation be amplified through the use of G-Proteins? |
1. A single receptor can activate multiple G proteins successively.
2. Activated G proteins activate effector enzymes generating second messengers 3. Secondary messengers may activate further effector enzymes. The signal is now amplified from a single receptor activation to many multiple effectors being activated - causing a diverse range of effects. |
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What are the critical subunits of phospholipase C isoform beta? |
C2 domain (shared by all PLC isoforms) - binds acidic phospholipids The Beta isoform has a special G-Protein interaction domain |
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PLC beta isoform creates two secondary messengers. 1. What are they? 2. How are they formed? |
1. 1,2 Diacylglycerol and Inositol 1,4,5 trisphosphate
2. Through the cleavage of Phosphatidylinositol 4,5-bisphosphate or PtdIns(4,5)P2, also known simply as PIP2 |
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How is calcium ion release mediated by PLC beta isoform? |
The secondary messenger Inositol 1,4,5 trisphosphate releases Ca2+. |
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What is the four parameter logistic (4PL) regression? |
In statistics regression analysisis is a statistical process for estimating the relationships among variables. The four parameter logistic (4PL) regression is commonly used for curve fitting analysis in bioassays. It shows a sigmoidal (s shaped) curve. |
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What are the critical domains of Protein Kinase C? |
2 x C1 Domains 1 x C2 Domain 1 |
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How is Protein Kinase C activated? |
2 x diacylglycerol binds to C1 domains (C1A / C1B) and 2 calcium ions bind to the C2 Domain thus associating protein kinase C with the membrane. |
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How is the messenger system of protein kinase C terminated? |
1. InsP3 --> inositol 2. Calcium release may cease 3. Diacylglycerol --> metabolised 4. PCK dissociates from the membrane |
