1. Introduction

A hurricane is being influenced by minor perturbations such as the flapping of the wings of a distant butterfly. The cell is the basic structural and functional unit of living systems, but how cell orchestrates its responses to stimuli from the intracellular or extracellular environment remains a fundamental question in biology. A tiny variation in these environments will elicit a series of biochemical events known as the cascade reactions inside the cell through signal transduction pathways. The consequences of such cascade reactions depend on cell type and can lead to changes in metabolism, gene or protein expression, morphology and cell cycle regulation. The interior and exterior environments of the cell are separated by the cell membrane, a lipid bilayer composed mainly of phospholipids and embedded proteins. The intracellular environment, termed the cytoplasm, is bounded by this membrane and consists of the cytosol and the cell’s organelles, which house the most important biochemical functions of the cell. However, many of the signaling molecules that mediate signal transduction pathways are located at the extracellular domain of the cell membrane and are excluded from the cytoplasm by this barrier. Like intracellular signal transduction, transmembrane signal transduction plays a key role in cell living process and must rely on these external molecules. This thesis discusses the transmembrane signal transduction study, using the calcium modulated T cell receptor (TCR) activity as a model.