Pathways relay signals from receptors to cellular responses

Pathways relay signals from receptors to cellular responses...

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Pathways relay signals from receptors to cellular responses. Signal-transduction pathways act like falling dominoes. The signal-activated receptor activates another protein, which activates another, and so on,  until the protein that produces the final cellular response is activated. The relay molecules that relay a signal from receptor to response are mostly proteins. The interaction of proteins is a major theme of cell signaling. Protein interaction is a unifying theme of all cellular regulation. The original signal molecule is not passed along the pathway and may not even enter the  cell. It passes on information. At each step, the signal is transduced into a different form, often by a conformational  change in a protein. The conformational change is often brought about by phosphorylation. Protein phosphorylation, a common mode of regulation in cells, is a major mechanism of signal transduction.
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Unformatted text preview: The phosphorylation of proteins by a specific enzyme (a protein kinase ) is a widespread cellular mechanism for regulating protein activity. Most protein kinases act on other substrate proteins, unlike tyrosine kinases that act on themselves. Most phosphorylation occurs at either serine or threonine amino acids of the substrate protein (unlike tyrosine phosphorylation in tyrosine kinases). Many of the relay molecules in a signal-transduction pathway are protein kinases that act on other protein kinases to create a “phosphorylation cascade.” Each protein phosphorylation leads to a conformational change because of the interaction between the newly added phosphate group and charged or polar amino acids on the protein. Phosphorylation of a protein typically converts it from an inactive form to an active form....
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