1. Epinephrine binding to the ai-adrenoreceptor activates the phosphoinositide s
ID: 262000 • Letter: 1
Question
1. Epinephrine binding to the ai-adrenoreceptor activates the phosphoinositide signaling system. Describe how activation of this pathway can lead to increased concentrations of Ca2+ within the cell. 2. A certain metabolic reaction takes the form A - B. Its standard free energy change is 7.5 kJ mol-'. a) Calculate the equilibrium constant for the reaction at 25°C. b) Calculate AG at 37°C when the concentration of A is 0.5 mM and the concentration of B is 0.1 mM. c) Is the reaction spontaneous under these conditions? 3. Almost all aerobic cells contain the enzyme catalase, which serves to protect them by degrading the otherwise toxic H2O2. Almost all cells have the enzyme inorganic pyrophosphatase. Does this mean that PPi is toxic? If not, what is the reason for the almost universal occurrence of this enzyme? 4. Describe two of the criteria given to account for the high phosphate group transfer potential of ATP. 5. When a bacteria culture carries out alcoholic fermentation, pyruvate is decarboxylated to acetaldehyde. In which position(s) of 14C-labeled glucose, would the radioactive 14C atom(s) have to be located in order to ensure that all of the pyruvate was labeled with 14C in its carboxyl group? Support your answer.Explanation / Answer
1. Epinephrine binds to the 7 Transmembrane alpha adrenergic receptor. Binding to the receptor activates phospholipase C which initiates the phosphoinositide cascade. Initiation of phosphoinositide cascade will increase the level of Inositol 1,4,5 triphosphate( IP3). Phospholipase C hydrolyzes the membrane PIP2 to IP3 and Diacylglycerol (DAG). IP3 induces the release of Ca+2 from the stores of the endoplasmic reticulum.
3. PPi is not toxic to cells. PPi generally occurs in blood plasma, synovial fluid, and urine in sufficient levels that block calcification and function as a natural inhibitor for the formation of hydroxyapatite in extracellular fluid (ECF).
Inorganic pyrophosphatase cleaves PPi into 2 phosphate ions. This reaction is exergonic, release heat and is generally coupled with unfavorable reactions driving them to completion. The enzyme plays a role in calcium absorption, lipid metabolism, bone formation, DNA synthesis and other biochemical reactions.
4. ATP has 3 phosphate groups - alpha, beta, and gamma. The gamma phosphate of ATP is situated farthest from the sugar ribose and has a higher energy of hydrolysis ( compared to alpha and beta). So, when the gamma phosphate is hydrolyzed, more energy is produced which makes ATP the high energy molecule.
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