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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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