#cAMP

Gene regulation in Prokaryotes

CAP-cAMP complex binds when

Catabolite repression couples glucose availability to cyclic AMP synthesis via adenylate cyclase. When glucose transport is low, EIIA phosphorylated activates cyclase, raising cAMP levels. Cyclic AMP binds catabolite activator protein CAP, inducing conformational shift allowing dimerization and DNA recognition. The CAP-cAMP complex binds conserved sites near catabolite-sensitive promoters including lac, ara, gal, facilitating RNA polymerase recruitment through alpha-CTD contact. When glucose abundant, cAMP falls, CAP remains inactive, transcription of alternative sugar operons reduced. Thus CAP-cAMP binding specifically signals carbon starvation and glucose limitation, coordinating hierarchical sugar utilization for energy efficiency.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8: Bacterial Transcription Control and CAP-cAMP

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Lac Operon

CAP becomes active when bound to

Catabolite activator protein exists in equilibrium between inactive and active conformations controlled by small molecule ligand binding allosterically. Each protomer of the homodimer contains N-terminal cyclic-nucleotide-binding domain that specifically accommodates cyclic AMP in anti conformation. cAMP binding triggers hinge repositioning and ordering of C-terminal helix-turn-helix DNA recognition motif able to bind consensus TGTGA-N6-TCACA half sites with high affinity. Resulting CRP-cAMP-DNA ternary complex bends DNA and activates transcription initiation. ATP and GTP do not serve as allosteric effectors for this protein, glucose actually lowers cAMP indirectly via PTS-mediated regulation of adenylate cyclase enzymatic activity controlling synthesis.

Ref: NCBI Biochemistry - CAP becomes active when bound to cAMP allosteric activation; Alberts Chapter 7 catabolite repression

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A Cell Signaling

Addition of cAMP in PKA knockdown cells causes:

No transcriptional change, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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A Cell Signaling

Which hormone uses cAMP as second messenger?

Calcitonin, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Second messenger in olfactory signaling is

cAMP, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Phosphodiesterase terminates GPCR signaling by converting

Cyclic-nucleotide phosphodiesterases hydrolyze cAMP or cGMP to the corresponding inactive 5'-monophosphates, thereby terminating the second-messenger signal. Regulation of phosphodiesterase activity provides an important mechanism for controlling the duration and amplitude of cyclic-nucleotide signaling in cells. These enzymes are important pharmacological targets for modulating cyclic nucleotide levels. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Second messenger decreased by Gαi signaling is

cAMP, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Second messenger increased by Gαs signaling is

cAMP, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Pertussis toxin causes increased cAMP because it

Pertussis toxin ADP-ribosylates Gαi, preventing the inhibitory G protein from interacting with receptors and thereby blocking its ability to inhibit adenylyl cyclase. The resulting loss of tonic inhibition elevates cAMP levels and contributes to the pathogenesis of whooping cough. The toxin has also become a valuable experimental tool for identifying Gi-coupled pathways.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Effect of cholera toxin on Gαs is

Cholera toxin catalyzes ADP-ribosylation of Gαs, locking the subunit in its GTP-bound active form by inhibiting GTPase activity. Persistent activation of adenylyl cyclase produces massive elevations of cAMP in intestinal epithelial cells, leading to continuous opening of chloride channels and the characteristic watery diarrhea of cholera. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Phosphodiesterase terminates signaling by

Cyclic-nucleotide phosphodiesterases hydrolyze cAMP or cGMP to the corresponding inactive 5'-monophosphates, thereby terminating the second-messenger signal. Regulation of phosphodiesterase activity provides an important mechanism for controlling the duration and amplitude of cyclic-nucleotide signaling in cells. These enzymes are important pharmacological targets for modulating cyclic nucleotide levels. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

Adenylyl cyclase converts

Adenylyl cyclase catalyzes the conversion of ATP to the second messenger cyclic AMP. The enzyme is stimulated by GTP-bound Gαs and inhibited by GTP-bound Gαi. The resulting changes in cAMP concentration regulate protein kinase A and cyclic-nucleotide-gated channels, linking G-protein-coupled receptors to diverse physiological responses. Careful

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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