COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for CSIR-UGC NET/JRF, SLET, GATE, and other entrance tests: CELL COMMUNICATION AND CELL SIGNALLING – Cell Signalling and Signal Transduction.
Syllabus Outline
- Hormones and their receptors.
- Cell surface receptor and signalling through G-protein coupled receptors.
- Signal transduction pathways and second messengers.
- Regulation of signalling pathways.
- Bacterial and plant two-component systems.
- Light signalling in plants.
- Bacterial chemotaxis and quorum sensing.
This quiz contains concept-based, most frequently asked 25 MCQs of “CELL COMMUNICATION AND CELL SIGNALLING – Cell Signalling and Signal Transduction”. Each question has a single correct/most appropriate answer.
*****
1. Which statement best describes the structure and function of the DNA-binding domain in nuclear receptors?
A) It contains a zinc finger that interacts with co-activators, while the C-terminal region controls dimerisation.
B) It consists of two zinc finger modules for DNA sequence recognition and receptor dimerisation.
C) It uses a basic helix-loop-helix motif stabilised by a zinc finger to bind DNA.
D) The N-terminal domain controls it in the presence of a zinc finger as a cofactor.
2. A chimeric receptor contains the ligand-binding domain of the estrogen receptor and the DNA-binding domain of the glucocorticoid receptor. What happens when estrogen is added?
A) Estrogen-responsive genes are activated.
B) Both estrogen and glucocorticoid-responsive genes are activated.
C) Both estrogen and glucocorticoid-responsive genes are inactivated.
D) Glucocorticoid-responsive genes are activated.
3. Which component is uniquely found in plant G-protein signalling?
A) Regulator of G-protein signalling proteins
B) GTPase-accelerating proteins
C) Extra-large Gα subunits with atypical structure
D) Seven-transmembrane G-protein-coupled receptors
4. Which observation indicates that a receptor signals through a Gαq pathway?
A) Inhibition of phospholipase C blocks the response
B) Increased intracellular cAMP levels
C) The receptor shows tyrosine kinase activity
D) The response is dependent on Inositol 1,4,5-trisphosphate (IP₃) levels
5. What is the immediate effect of rhodopsin activation in rod cells?
A) Activation of adenylyl cyclase, increasing cAMP and opening cation channels
B) Activation of phosphodiesterase, reducing cGMP and closing cation channels
C) Activation of phospholipase C and calcium release
D) Opening of potassium channels and depolarisation
6. What happens when a non-hydrolyzable GTP analogue is used instead of GTP in a G-Protein–Coupled Receptor signalling assay?
A) Adenylyl cyclase activity rises briefly and then declines
B) G-protein subunits fail to dissociate
C) G-Protein–Coupled Receptor signalling is inhibited
D) Adenylyl cyclase remains continuously active
7. How does Inositol 1,4,5-trisphosphate (IP₃) increase intracellular calcium levels?
A) It activates voltage-gated calcium channels at the plasma membrane
B) It diffuses to the endoplasmic reticulum and opens calcium channels
C) It binds calmodulin to release bound calcium
D) It acts in the nucleus to increase calcium channel expression
8. What is the correct sequence of events in the Ras–MAPK pathway?
A) RTK → SOS → Grb2 → Ras → MEK → Raf → ERK
B) RTK → Grb2 → SOS → Ras → Raf → MEK → ERK
C) RTK → Ras → Grb2 → SOS → Raf → MEK → ERK
D) RTK → Raf → Ras → MEK → Grb2 → SOS → ERK
9. How do Regulator of G-protein Signalling proteins terminate G-protein signalling?
A) By competing with ligands for G-Protein–Coupled Receptor binding
B) By inhibiting the βγ subunit
C) By removing GTP from Gα
D) By accelerating GTP hydrolysis on the Gα subunit
10. What is the correct sequence of phosphorylation in a bacterial two-component system?
A) Sensor kinase phosphorylates serine → transfers to threonine on the response regulator
B) Sensor kinase phosphorylates histidine → transfers to aspartate on the response regulator
C) A soluble kinase phosphorylates tyrosine → transferred to aspartate
D) Response regulator autophosphorylates and transfers phosphate to a transcription factor
11. Which amino acid residue is phosphorylated in the receiver domain of plant response regulators?
A) Histidine
B) Tyrosine
C) Aspartate
D) Glutamate
12. What is the likely effect of mutating the conserved aspartate residue in a response regulator to glutamate?
A) Loss of signalling due to failure of phosphorylation
B) Constitutive activation of the pathway
C) Change in signalling output due to failure of phosphorylation
D) Inhibition of the kinase due to failure of phosphorylation
13. What signal activates the VirA sensor kinase in Agrobacterium tumefaciens?
A) Acetosyringone
B) cAMP
C) Acyl-homoserine lactones
D) Virulence gene expression in wounded plants
14. How does phytochrome activation occur and initiate signalling?
A) Pr absorbs far-red light to form active Pfr and activates cytoplasmic G-proteins
B) Pr absorbs red light to form active Pfr and interacts with PIFs
C) Pfr absorbs red light to convert into Pr and phosphorylate COP1
D) Both Pr and Pfr forms act as membrane ion channels in the presence of red light and far-red light, respectively.
15. What distinguishes phytochrome A from other phytochromes?
A) It is light-labile and rapidly degraded under red light.
B) It remains active under red light and far-red light.
C) It signals through G-Protein–Coupled Receptor pathways.
D) It remains in the Pr form under red light as well as far-red light.
16. What phenotype is expected in a Phytochrome-Interacting Factors (PIFs) quadruple mutant grown in darkness?
A) Enhanced elongation and closed cotyledons
B) No difference from wild type
C) Constitutive photomorphogenesis
D) Failure to germinate
17. How does UVR8 respond to UV-B light?
A) Undergoes chromophore isomerisation
B) Is activated by proteolytic cleavage
C) Binds a chromophore after UV exposure
D) Dissociates from a dimer into active monomers
18. Which enzymes are responsible for sensory adaptation in bacterial chemotaxis?
A) CheA and CheY
B) LuxI and LuxR
C) CheW and CheZ
D) CheR and CheB
19. What is the core mechanism of quorum sensing in Vibrio fischeri?
A) A phosphorelay system using histidine kinases
B) A positive feedback loop where LuxI produces AHL that activates LuxR
C) A two-component system that represses gene expression
D) Accumulation of cyclic-di-GMP
20. What is the chemical nature of the Autoinducer-2, a quorum-sensing signalling molecule used by many bacteria for cell–cell communication?
A) Oligopeptide
B) Furanosyl borate diester
C) Acyl-homoserine lactone
D) Cyclic dinucleotide
21. Which of the following statements about G-Protein–Coupled Receptors (GPCRs) are correct?
I – GPCRs have seven transmembrane α-helices.
II – The N-terminus is located in the cytoplasm.
III – GPCRs function as monomers.
IV – Ligand binding promotes GDP–GTP exchange on Gα.
A) I and II
B) II and III
C) I and IV
D) III and IV
22. Which statements about cytokinin signalling are correct?
I – Cytokinin binds to histidine kinases.
II – Signal transfer occurs directly without intermediates.
III – Arabidopsis Histidine Phosphotransfer proteins shuttle phosphate into the nucleus.
IV – Type-B Arabidopsis Response Regulators act as transcription factors when phosphorylated.
A) I, II, and IV
B) I, III, and IV
C) II, III, and IV
D) I and IV only
23. Which statements about Phytochrome-Interacting Factors (PIFs) are correct?
I – PIFs promote growth in darkness
II – PIFs are stabilised by interaction with Pr
III – PIFs are degraded after light-induced phosphorylation
IV – PIFs act together with HY5 to promote photomorphogenesis
A) I and II
B) I and III
C) II and IV
D) III and IV
24. Assertion (A): A single activated G-Protein–Coupled Receptor can activate multiple G-proteins, leading to signal amplification.
Reason (R): The G-Protein–Coupled Receptor phosphorylates multiple Gα subunits to activate them.
A) Both A and R are true, and R explains A
B) Both A and R are true, but R does not explain A
C) A is true, but R is false
D) A is false, but R is true
25. Assertion (A): Calmodulin is a calcium sensor without enzymatic activity.
Reason (R): Binding of calcium induces a conformational change that allows calmodulin to activate target proteins.
A) Both A and R are true, and R explains A
B) Both A and R are true, but R does not explain A
C) A is true, but R is false
D) A is false, but R is true
*****
Previous: Host-Parasite Interactions and Signalling
Next:
References
- Nelson, David L. & Cox, Michael M. (2021). Lehninger Principles of Biochemistry, W. H. Freeman, 8th Edition.
- Willey, J. M., Sandman, K. M., & Wood, D. H. (2022). Prescott’s Microbiology, McGraw-Hill, 12th Edition
- Kuby, J., Kindt, T. J., Osborne, B. A., & Goldsby, R. A. (2019). Kuby Immunology, W. H. Freeman, 8th Edition.
- Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., & Walter, P. (2014). Molecular Biology of the Cell, Garland Science, 4th Edition.
- Geoffrey Cooper and Kenneth Adams (2022). The Cell: A Molecular Approach, Oxford University Press, 9th Edition
- Robert A Weinberg, Robert A. Weinberg (2006). The Biology of Cancer, Taylor & Francis, 1st Edition.
- Gupta, P.K. (2022). Cell and Molecular Biology, Rastogi Publications, 5th Edition.
🔗 Explore More MCQs:
