64. Binding of a ligand to a cell-surface receptor activates an intracellular signal transduction pathway through the sequential activation of four protein kinases. In the human cell line A, these kinases are held in a signaling complex by a scaffolding ‘protein whereas in another cell line B/these kinases are freely diffusible. Which one of the following possibilities do you think is NOT correct?
(1) Speed of signal transduction will be higher in cell A.
(2) Possibility of cross-linking with other signal transduction pathways will be lesser in correct?
(1) KI inhibits K2 (2) K2 inhibits K1
(3) K1 activates K2 (4) K2 activates K1
Scaffold Proteins and Kinase Signaling Efficiency: What Is Not Correct?
Introduction
Binding of a ligand to a cell-surface receptor can activate an intracellular signaling cascade involving multiple protein kinases. These kinases can either be organized into a scaffolding complex or be freely diffusible inside the cell.
Cell Line A: Scaffolded Kinases
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Kinases are physically tethered by a scaffold protein.
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This arrangement facilitates rapid and efficient signal relay.
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Limits unwanted cross-talk by insulating signaling components.
Cell Line B: Freely Diffusible Kinases
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Kinases diffuse independently in the cytoplasm.
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Signal transduction tends to be slower due to lower local concentrations.
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Higher chance of cross-talk with other pathways due to diffusion.
Which Statement Is NOT Correct?
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Speed of signal transduction will be higher in cell A.
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Correct: Scaffold proteins accelerate signaling by colocalizing kinases and substrates ().
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Possibility of cross-linking with other signal transduction pathways will be lesser in cell A.
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Correct: Scaffold complexes insulate the pathway, reducing cross-reactivity ().
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Signal amplification will be higher in cell A.
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Correct: Scaffold proteins can increase the efficiency, amplifying signaling outcomes ().
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Scaffold proteins reduce the overall fidelity of signaling by restricting kinase mobility.
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Not correct: Scaffolds enhance signaling fidelity by organizing complexes and reducing promiscuous interactions ().
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Thus, a statement claiming scaffolds reduce fidelity or impair signaling speed is incorrect.
Kinase Interaction Directionality (Second Question)
Which is the correct relationship between kinases K1 and K2?
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(1) K1 inhibits K2
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(2) K2 inhibits K1
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(3) K1 activates K2
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(4) K2 activates K1
In a typical kinase cascade, an upstream kinase activates downstream kinases, thus K1 activates K2 (3) is the correct choice.
Summary
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Scaffold proteins accelerate and amplify signaling and reduce cross-talk, enhancing fidelity.
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Kinase cascades generally involve upstream kinases activating downstream kinases sequentially.
