TEXT, CHAPTER 7, PAGES 127, CHAPTER 11, PAGES 188-201

I. Introduction

        A. Cell signaling in the history of life

        B. Communicating cells may be close together or far apart

                1. Direct physical contact between plant and animal cells

                2. Communicating between cells, which are far apart.

                        Local Regulator

                        Hormone Signaling

                        First Messenger

        C. Three stages of cell signaling
                Dr. Earl W. Sutherland 1971
                a.   Reception

                b. Transduction

                c. Response


II. Signal Reception and the Initiation of Transduction

            A. Ligand and ligand binding


             B.  Most signal receptors are plasma-membrane proteins and water-soluble
                    a. G-Protein linked receptors
                    b. Tyrosine-Kinase Receptors
                    c. Ion-Channel Receptors

            C.  Intracellular Receptors

III. Signal Transduction Pathways

A. Pathways relay signals through relay molecules (proteins) from receptors to cellular responses.
B. Protein phosphorylation is a major mechanism of signal transduction.

        Protein phosphorylation

        Protein Kinase

        Protein Phosphates

C. Second messengers

        Second Messenger

        a.  Cyclic AMP:  Cyclic adenosine monophosphate, a second messenger.

        Example:  Cholera infection

        b. Calcium Ions

        c. Diacylglycerol (DAG) and inositol trisphosphate (IP3)

IV. Cellular Response to Signals

A. In response to a signal, a cell may regulate activities in the cytoplasm.
B. In response to a signal, a cell may regulate the synthesis of enzymes or other proteins,
    usually by turning specific genes on or off.

V. Two Important Benefits of the multisteps between the original signaling event at the cell surface and the cell’s response.

                       A. Signal amplification

                       B.  The specificity of cell signaling


First messenger – The extracellular signal molecule that binds to the membrane receptor, the signal transduction pathway’s first messenger.

Hormones signaling - Specialized cells release hormone molecules into vessels of the circulatory system, by which they travel to target cells in other parts of the body.

Ligand – A molecule that binds specifically to a receptor site of another molecule.

Local regulator –A substance that influences cells in the vicinity.  e.g. growth factors, nerve cells, neurotransmitter .

Plasmodesma – An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells.

Protein kinase – General name for an enzyme that transfers phosphate groups from ATP to a protein

Protein phosphorylation – A chemical reaction, activating a protein by adding one or more phosphate groups to it by protein kinase.

Protein phosphatase – Enzymes that remove phosphate groups from proteins and reverse the effects of protein kinase.

Second messengers – Small, nonprotein, water-soluble molecules or ions, involved in signaling pathway.  They can readily spread throughout the cell by diffusion.