The activity of regulatory enzymes is controlled by internal signals that reflect the conditions in a particular cell. Internal signals include substrate availability, cofactor availability, activators/inhibitors, and feedback inhibition. On the other hand, the activity of regulatory enzymes are also controlled by external signals that provide information about conditions in the organism. External signals include activators/inhibitors and hormones, which usually mediate the phosphorylation or dephosphorylation of pathway components. Hormones are chemical signals produced in response to specific conditions and distributed throughout an organism via the bloodstream. They are the primary method of regulation used to control metabolic reactions. Hormones interact with target cell receptors in order to alter the behavior of the cell. Only cells with receptors for a hormone response, and receptor proteins are specific, interacting with one or a few hormones. The same hormone can cause different responses in different cells, even if it interacts with the same receptor. Hormones binding to cell membrane receptor proteins function via a amplification mechanism.
Recent comments