Cell-Cell Interactions 7.1 Cells signal one another with chemicals. Receptor Proteins and Signaling Between Cells • Receptor proteins are located on or within the cell, and have three-dimensional shapes that fit the shape of specific signal molecules. (p. 126) • Binding of the signal molecule with the receptor protein induces a change in the protein's shape and produces a cellular response. (p. 126) • Immunochemistry and molecular genetics are being used to locate and characterize receptor proteins. (p. 126) Types of Cell Signaling • Cells can communicate through any of four basic mechanisms: direct contact, paracrine signaling, endocrine signaling, or synaptic signaling. (p. 127) 7.2 Proteins in the cell and on its surface receive signals from other cells. Intracellular Receptors • All cell-signaling pathways share certain common elements, including a chemical signal that passes from one cell to another and a receptor that receives the signal in or on the target cell. (p. 128) • Intracellular receptors may trigger a variety of responses in the cell, dependent on the receptor. (p. 128—129) Cell Surface Receptors • Cell surface receptors convert the extracellular signal to an intercellular one, responding to the binding of the signal molecule to the cell's outside by producing a change inside the cell. (p. 130) • Many cell surface receptors either act as enzymes or are directly linked to enzymes. (p. 130) • G-protein-linked receptors activate an intermediary protein, which then effects the intercellular change. (p. 131) 7.3 Follow the journey of information into the cell. Initiating the Intracellular Signal • Second messengers, such as cAMP and calcium ions, relay messages from receptors to target proteins. (p. 132) Amplifying the Signal: Protein Kinase Cascades • Some surface receptors generate large intracellular responses because each stage of the pathway amplifies the next, causing a cascading effect. (pp. 134—135) 7.4 Cell surface proteins mediate cell—cell interactions. The Expression of Cell Identity • As an organism develops, its cells acquire their specific identities by controlling gene expression, turning on the specific set of genes that encode the particular functions of each cell type. (p. 136) • Every cell contains surface marker proteins that uniquely identify each cell type. (p. 136) Intercellular Adhesion • Cells attach to one another using cell junctions. (p. 137) • Tight junctions connect the plasma membranes of adjacent cells in a sheet. (p. 138) • Anchoring junctions mechanically attach the cytoskeleton of a cell to the cytoskeletons of other cells or to the extracellular matrix. (p. 138) • Communication junctions allow communication with adjacent cells through direct connections. (p. 140) | ||||||
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