The sensitivity of a cell to a particular chemical messenger is dictated by which factor?

The sensitivity of a cell to a specific chemical messenger is primarily determined by the presence of functional domains on its receptor proteins. Functional domains are regions in a receptor that engage with the chemical messenger and initiate a physiological response. These domains can influence how well a receptor binds to a messenger, the nature of the binding, and the subsequent signal transduction pathways that are activated.

For instance, variations in the amino acid sequences within these functional domains can lead to differences in receptor affinity for the messenger, ultimately impacting how effectively the cell can respond to that messenger. Cells can increase or decrease their sensitivity to a messenger by altering the expression levels of these receptors or modifying their functional domains through processes like phosphorylation, glycosylation, or other post-translational modifications.

While the ligand-binding domain is crucial for the interaction between the ligand and receptor, it is the broader context of functional domains that encapsulates the entire mechanism of response, including receptor activation and downstream signaling. The characteristics of the chemical messenger itself do influence its effectiveness but do not solely dictate the cell's sensitivity. Thus, the functional domains play the main role in determining how a cell reacts to a specific chemical signal.