Question

Multiple Choice Which of the following are true of G protein coupled receptors (GPCRs) A) peripheral membrane protein B) Activates G proteins on cytoplasmic side C) Receptors to lipid soluble hormones D) Binds ligands on cytoplasmic side Submit CASTILLO NAVA Invoice Soon

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Answer 1

Question 1

Answer: G protein coupled receptors are transmembrane receptor protein. It has seven transmembrane spaning domains. Ligands binds to the extracellular side of the cell and trasmits the signal to G protein on the cytoplasmic side. Hence, option A and D are incorrect. Various ligands such hormones, neurotransmitters nd phermones etc., binds to G protein couple receptors and transmit the signal to G protein. Water soluble hormones acts as ligands for GPCRs but not lipid solube hormones So, Option C is the incorrect answer and Option B is the correct answer.

Question 2

Answer: G Protein are membrane associated protein that is present on the cytoplasmic side of the membrane. They are either monomeric or heteroteimeric proteins. Hence, A, C, and D are incorrect. Various ligands molecules binds to G protein couple receptors and transmit the signal to G protein. Hence, G protein works in association with G protein coupled receptors. The correct answer is Option B.

Question 3

Answer: G protein is an heterotrimeric protein made of α, β, and γ subunits and are intracellular. These subunits dissociates when bound to GTP and remain associated when bound to GDP. G protein does not bound to ATP. Hence, Options A, B and D are incorrect. The α-subunit gets activated when bound to GTP and activates enzymes. So, option C is the correct answer.

Question 4

Answer: Ligands binds to G protein coupled receptor on the extracellular side and activates G protein by replacing GDP that is bound to α-subunit of G protein with GTP. Hence, option A is correct and Option B is incorrect. Binding of the GTP to α-subunit decreases its affinity to β, and γ subunits and hence, α-subunit gets diassociates from β, and γ subunits. Hence, Option C is incorrect and option D is correct. The correct answers are Options A and D.