6) G-protein coupled-receptors... a. are ligand-gated channels b. activate heter

Question

6) G-protein coupled-receptors... a. are ligand-gated channels b. activate heteromeric G-proteins c. have 5 subunits d. have 6 transmembrane segments 7) Refer to the images of the synaptic terminals at two different temperatures to answer the following question 19°C 25°C B. You are told this fly is a temperature-sensitive dynamin mutant that causes the dynamin protein to unfold at warm temperatures (25°C). Which one of the following does NOT happen when the flies are warmed? a. Dynamin fails to pinch-off vesicles b. The synaptic terminal swells due to the accumulation of membrane c. Synaptic vesicles accumulate in the synaptic terminal d. Endocytosis is disrupted 8) Which second messenger acts directly to mediate the release of Ca2" from the endoplasmic reticulum? a. Diacylglycerol (DAG) b. Inositol triphosphate (IP3) c. CAMP d. cGMP

Explanation / Answer

6. GPCR (G-protein coupled receptor) is the largest cell surface receptors. These receptors are ligated gated channels that get activated by the binding of the ligands. The receptors have seven transmembrane domains and all have a similar structure. These receptors are associated with heteromeric G-proteins which are composed of three subunits. when the ligand binds to the receptor, the G-protein gets activated by the conversion of GTP to GDP. This results in the dissociation of the activated G-protein into alpha complex and beta-gamma complex. Both the complexes can diffuse along the membrane and initiate the target protein activity. So, the correct options are a and b.

7.The given images depict the functioning of the synaptic terminals at two different temperatures. Here it is said that the fly is temperature-sensitive and with a rise in temperature the dynamin protein unfolds. the unfolding of the dynamin protein will result in the loss of the function of the protein. the dynamin protein is responsible for the formation of the vesicles during the synaptic vesicle endocytosis occurring during the synaptic transmission. Since the dynamin unfolds at higher temperatures the formation of the vesicles disrupts. This means that the endocytosis gets disrupetd. So, the options a, b, and d will take place as the fly gets warmed and unfolding of dynamin takes place. The option c will not take place because the dynamin protein is responsible for the formation of vesicles and when the endocytosis of the vesicles gets disrupted, the accumulation of the vesicles in the synaptic terminal is not possible.

8. The correct option is b inositol triphosphate. IP3 is a small molecule that gets released into the cytosol for the signaling of the Ca2+ release. The IP3 binds to the receptors present in the endoplasmic reticulum and results in the release of the calcium.

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