…Is how cells coordinate their physiological behaviors …Greater than the sum of their subcellular organelles

Integrate the complexities of… Endocrinology (the study of hormones), Cell biology, Enzyme kinetics, and Biochemistry …see emerge the cooperative and not so cooperative molecular interactions between cells. When cell-to-cell communication is unsuccessful, a result can be a harmful absence of cooperation, which may emerge as tumors or cancer, adult-onset diabetes, developmental abnormalities…

Most cell-to-cell communication involves chemical signaling …Chemicals that freely diffuse between cells, …Chemicals received by a cell through cell-to-cell contact …Chemicals that freely diffuse from one cell’s cytoplasm to another’s via junctions directly linking the cytosol of adjacent cells. Signals can be byproducts of cellular metabolism that one cell releases essentially as waste or without intending to initiate a signal (lactic acid) Signals can be purposeful in the sense that one cell is sending a signal meant to be received and interpreted in a certain way by another cell (hormone)

Local Regulator: released into the intercellular space (synapses) Systemic Diffusion: carried by the blood or lymph (hormones)

Three stages of cell signaling (signal-transduction pathway) We can biochemically differentiate the communication events of these chemical signals into three stages: Reception (by a cell) Transduction (from outside of the cell to inside the cell) Response (how the cell responds to having received the signal)

Reception of a chemical signal ….the attachment (or association) of the chemical signal to some aspect of the recipient cell’s plasma membrane A membrane …requirement for the occurrence of subsequent signal transduction and response (i.e., cell-to-cell signaling typically requires that recipient cells are intact)

Transduction (signal transduction) …represents the middle stage of communication …the conversion of the reception signal at the surface of the cell to a signal that directly facilitates a response …involves a number of steps (complex) …signal transduction purpose is for— linking reception and response Additionally …the plasma membrane receptor and the molecules involved in the response are not always located in the same region of the cell. So intracellular signals (often chemical) serve to physically connect reception and response For example, a signal-transduction pathway may involve the following: …Reception (at the plasma membrane)  …Transduction (through the cytoplasm)  …Response (in the nucleus, e.g., transcription)

Response The response to cell signaling varies enormously …..Depends on the signal …..Depends on the receiving cell …..Involves either the turning on of a specific (often enzymatic) activity (including the synthesis of new enzymes) or a reduction in (or turning off of) a specific enzymatic activity …..May involve the turning on or off of more than one activity Different kinds of cells have different collections of proteins. The response of a particular cell to a signal depends on its particular collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response. Consider response to be simply some end point of a signal-transduction pathway