Engineering Questions with Answers - Multiple Choice Questions

MCQs on Cell Signaling and Signal Transduction – G-protein Receptors and Messengers

1 - Question

G-protein coupled receptors are referred to as seven-transmembrane receptors.
a) True
b) False

View Answer

Answer: a
Explanation: G-protein coupled receptors (GCPRs) are called so because they interact with the GTP-binding proteins – G-proteins. These are also called 7TM because they consist of 7 transmembrane helices.




2 - Question

The G-protein coupled receptors have their _____________________ outside the cell.
a) amino terminus
b) carboxyl terminus
c) alpha helices
d) beta helices

View Answer

Answer: a
Explanation: The G-protein coupled receptors have their amino-terminus outside the cell and carboxyl-terminus inside the cell. The 7 transmembrane helices (alpha-helices) traverse the plasma membrane.




3 - Question

On the cytoplasmic site of GCPRs, the G-proteins bind to ___________________
a) amino-terminus
b) promoter region
c) second loop
d) third loop

View Answer

Answer: d
Explanation: There are 3 loops of G-protein coupled receptor located on the outside of the cell and 3 loops located on the cytoplasmic site. The G-proteins bind to the third intracellular loop while the loops located outside the cell form the ligand-binding active site.




4 - Question

. Which of the following is a stimulus for rhodopsin?
a) light
b) acidic pH
c) basic pH
d) neurotoxins

View Answer

Answer: a
Explanation: Rhodopsin is a very stable G-protein coupled receptor. This receptor is always bound to a retinal group (the ligand). Rhodopsin is also a biological pigment in the retina and is very sensitive to light.




5 - Question

The inactive conformation of a G-protein coupled receptor is stabilized by ____________________
a) covalent interactions
b) hydrogen binding
c) non-covalent interactions
d) ionic interactions

View Answer

Answer: c
Explanation: The inactive conformation of the G-protein coupled receptor is stabilized by non-covalent interactions between the residues in the transmembrane alpha helices. Rotation or movements in these loops cause changes in the conformation of cytoplasmic loops.




6 - Question

. The G-proteins bind only to _________________
a) cytosine
b) guanine
c) thymine
d) adenine

View Answer

Answer: b
Explanation: The G-proteins are called so because they bind only to the guanine nucleotides – GTP (guanosine triphosphate) and GDP (Guanosine diphosphate). The protein is heterotrimeric and consists of three different polypeptides subunits.




7 - Question

Desensitization is the process of blocking receptors from turning on ______________
a) G-proteins
b) Transcription factors
c) Promoters
d) Activators

View Answer

Answer: a
Explanation: Desensitization is the process of preventing the G-protein coupled receptors from turning on additional G-proteins to regain sensitivity for future stimulus. The activated receptors turn on G-proteins and the latter then turns effectors on, and all of them must remain inactive to be able to respond to future stimulus.




8 - Question

. Arrestins compete with ________________ for binding with G-protein coupled receptors.
a) Effectors
b) Primary messengers
c) Secondary messengers
d) G-proteins

View Answer

Answer: d
Explanation: Arrestins are small group of proteins that bind to the G-protein coupled receptors. To bind to these receptors, the arrestins compete with heterotrimeric G-proteins. In the process of desensitization, arrestin binding prevents further activation of the G-proteins.




9 - Question

. Retinitis pigmentosa is an inherited disorder caused due to mutation in the gene that encodes for __________________
a) G-proteins
b) Arrestin
c) Rhodopsin
d) G-protein receptor kinase

View Answer

Answer: c
Explanation: Retinitis pigmentosa (RP) is an inherited disorder characterized by progressive degeneration of the retina and eventual blindness. The disease is caused due to mutation in a gene that encodes the visual pigment of rods – rhodopsin.




10 - Question

Adenoma is caused by the over-secretion of ____________________
a) arrestin
b) rhodopsin
c) kinetin
d) thyroid hormone

View Answer

Answer: d
Explanation: Adenoma is a benign thyroid tumor that caused due to the secretion of large quantities of thyroid hormone without having to be stimulated by the pituitary hormone – thyroid stimulating hormone (TSH).




11 - Question

. A somatic mutation is present in all of the individual’s body cells.
a) True
b) False

View Answer

Answer: b
Explanation: A somatic mutation is present in one cell type of an individual, such as a thyroid cell in case of an adenoma, while an inherited mutation is present in all the cells of an individual. Somatic mutations are the primary cause of human cancer.




12 - Question

. The Kaposi’s sarcoma is caused by ____________________
a) Herpes virus
b) Adeno virus
c) Human immunodeficiency virus
d) Retro virus

View Answer

Answer: a
Explanation: The herpes virus, responsible for Kaposi’s sarcoma characterized by purplish skin lesions prevalent in AIDS patients, encodes a constitutively active receptor for interleukin-8.




13 - Question

. The Cholera toxin produced by Vibrio cholera exerts its effect by _____________________
a) modifying G-protein
b) modifying primary messengers
c) modifying effectors
d) modifying receptors

View Answer

Answer: a
Explanation: The cholera toxin exerts its effect by inhibiting the GTPase activity of G-proteins in the cells of intestinal epithelium and modifying their G-alpha subunits. This causes the epithelial cells to secrete large volumes of fluid into the intestinal lumen.




14 - Question

Epinephrine causes an increase in ____________________
a) blood glucose levels
b) surface receptors
c) rhodopsin pigments
d) mast cells

View Answer

Answer: a
Explanation: Epinephrine is called the “fight-or-flight” hormone produced by the adrenal gland in situations of stress. It causes an increase in blood glucose levels to deal with stressful situations.

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