1) recognising the messenger molecules and attaching to them to trigger series of chemical reactions in the body.
2) by attaching themselves with the foreign particle or part of a body which is to be engulfed by the cell surface membrane.
3) helping in cell adhesion ( attaching one cell to other cells to form tissues)
4) by acting as antigen or cell marker.
Signal transduction refers to the transmission of a molecular signal , in the form of a chemical modification.
This involves movement of protein complexes along a signaling pathway that ultimately triggers a biochemical event in a cell.
Signal transduction occurs when an extra cellular signalling molecule activates a specific receptor located on the cell surface or inside of he cell. This receptor triggers a biochemical chain of events inside the cell, that eventually elicits a response. This is called as the signalling cascade.
Depending upon th cell the response may alter the cells metabolism, shape, gene expression, or ability to divide.
The signal can be amplified at any step, thus , one signaling molecule can generate a response involving hundreds to millions of molecules.