Question

For a biological response activated by a cell signaling receptor due to stimulation by a related set of ligands (signaling molecules):

a) For any one particular type of ligand: Provide your best thinking about the mechanisms underlying the fact that the response is stronger when the concentration of ligand is higher.

b) A and B, a pair of structurally similar but different ligands, are presented separately but at the same concentration to separate samples of cells from a highly uniform cell population. The overall cellular response to ligand B is stronger than the response elicited by ligand A. Provide your best thinking about two most likely mechanisms underlying this differing response. Don't settle for a one-sentence answer - keep your comments very brief (just a few sentences), but provide a bit of depth/complexity in your answer.

Answer 1

a) If the receptors for a particular ligand is higher in number, increased concentration of ligands will actually trigger heightened signalling response. More number of ligands will bind to more number of recpetors leading to the increased number of secondary messengers and activated kinases which then activates more number of transcription factors to elicit the heightened cellular response of the ligand.

B) 1.The receptors for ligand B is more in number in the cell than ligand A. Ligand will always have to bind to a receptor to start a signalling pathway. If the receptors are less in number , the ligand might not elicit a strong cellular response.

2. Ligand B might be activating a signalling cascade which is involved in the activation of a set of transcription factors , or enhancers or a super enhancer which controls a set of gene products getting translated to proteins. This will lead to a heightened response for the signal.

Whereas ligand A must be activating a signalling pathway which is involved in production of a particular protein required in a minute quantities, which might not seem like a stronger response but is surely needed for the cell.