This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “G Protein-Coupled Receptors – Set 2”.
1. Which among the following is a distinctive feature of family 3 of the G protein coupled receptors?
a) 200-residue C-terminus
b) DNA domain
c) CLB
d) Peptide domain
View Answer
Explanation: In addition to having a unique primary sequence, Family 3 has other distinctive characteristics, such as an approximately 200-C-terminus residue and an approximately 600-N-terminus residue. The latter consists of a domain and a cysteine-rich domain-like putative Venus flytrap.
2. Which among the following is an example of the subset of family 3 of the G protein coupled receptors?
a) Metabotropic glutamate receptor
b) Opsin
c) Chemokine
d) FSH
View Answer
Explanation: The metabotropic glutamate receptors, an extracellular Ca2+-sensing receptor, and putative taste and pheromone receptors are members of family 3. A two Venus flytrap-like structure bound to the cysteine-rich region by a disulfide bridge has been confirmed as part of the extracellular N-terminus of the metabotropic glutamate receptors.
3. Which among the following terminus is involved in the ligand binding of most of the members of family 1 GPCRs?
a) Extracellular C-terminus
b) Intracellular N-terminus
c) Extracellular N-terminus
d) Intracellular C-terminus
View Answer
Explanation: In the case of family 1 GPCRs, the extracellular N-terminus is involved in the binding of ligands. These ligand classes include, hormones, neurotransmitters and other such molecules. Transmembrane domain is the major binding site of these ligands in GPCRs.
4. Retinal is the ligand of chemokines in GPCRs.
a) True
b) False
View Answer
Explanation: Retinal is the ligand of opsins. Among GPCRs, the opsins are distinctive in that the ligand retinal, in the seventh transmembrane helix is covalently bound to a lysine. Retinal enables the conversion of light into metabolic energy for some microorganisms.
5. The N-terminus and extracellular loops of Rhodopsin form a well-structured domain that occludes the site of retinal binding.
a) True
b) False
View Answer
Explanation: The N-terminus and extracellular loops of Rhodopsin form a well-structured domain that occludes the site of retinal binding. The receptors of hormones have a more open extracellular structure that facilitates the entry of ligands into the transmembrane domain.
6. After the initial binding to the peptide C-terminus in the family 2 receptors of GPCRs, the extracellular N terminus binds to which of the following domains?
a) DNA binding domain
b) Seven transmembrane domains
c) Ligand domain
d) CLB domain
View Answer
Explanation: The extracellular N-terminus is responsible for initial binding to the peptide C-terminus in Family 2 receptors. This is accompanied by the binding of the peptide N-terminus to the seven transmembrane domains.
7. In which place agonist binding of the metabotropic glutamate receptor occurs in the family 3 GPCRs?
a) Between the lobes of the Venus flytrap.
b) Between the C domain
c) Between the DNA binding cleft
d) Between the N terminal and C terminal
View Answer
Explanation: The agonist binding occurs inside a cleft between the lobes of the Venus flytrap for Family 3 GPCRs. This property is demonstrated by the metabotropic glutamate receptor’s three-dimensional form.
8. Which among the following tripeptide is important for G protein activation?
a) Eisenin
b) Peroxide
c) Glutathione
d) DRY
View Answer
Explanation: For G protein activation, a tripeptide ‘DRY’ motif (D/E, R, Y/W) at the juncture between the third transmembrane helix and the beginning of the second intracellular loop is critical. This is strongly conserved in the GPCRs of family 1.
9. In the 3D structure of a complex between rhodopsin and retinal G protein, C-terminal peptide of the latter binds to which of the amino acids of receptor’s DRY motif?
a) Arginine
b) Lysine
c) Leucine
d) Isoleucine
View Answer
Explanation: The three-dimensional structure of a complex between activated rhodopsin and a C-terminal peptide of the retinal G protein alpha-subunit indicates direct binding of the latter to the arginine of the DRY motif of the receptor. A number of studies have been carried out to identify the sites of ligand binding and G protein coupling of GPCRs.
10. What is the name of the mechanism in which there are multiple conformations between active and inactive forms of ligands in GPCRs?
a) Ligand directed signalling
b) Receptor directed signalling
c) DNA directed signalling
d) RNA directed signalling
View Answer
Explanation: Between the so-called active and inactive conformations, several conformational states can exist, with different ligands capable of promoting a particular conformation. This possibility has important effect for a given ligand’s downstream signalling effects, a phenomenon called ligand-directed signaling or ligand biased efficacy.
Sanfoundry Global Education & Learning Series – Molecular Endocrinology.
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