Chapter 7

Summary		Questions		Media Resources
7.1 Cells signal one another with chemicals.
• Cell signaling is accomplished through the recognition of signal molecules by target cells.		1.  What determines which signal molecules in the extracellular environment a cell will respond to? 2.  How do paracrine, endocrine, and synaptic signaling differ?		•Cell Interactions • Retrograde Messengers between Nerve Cells
7.2 Proteins in the cell and on its surface receive signals from other cells.
• The binding of a signal molecule to an intracellular receptor usually initiates transcription of specific regions of DNA, ultimately resulting in the production of specific proteins. • Cell surface receptors bind to specific molecules in the extracellular fluid. In some cases, this binding causes the receptor to enzymatically alter other (usually internal) proteins, typically through phosphorylation. • G proteins behave as intracellular shuttles, moving from an activated receptor to other areas in the cell.		3.  Describe two of the ways in which intracellular receptors control cell activities. 4.  What structural features are characteristic of chemically gated ion channels, and how are these features related to the function of the channels? 5.  What are G proteins? How do they participate in cellular responses mediated by G-protein-linked receptors?		•G Proteins
7.3 Follow the journey of information into the cell.
• There are usually several amplifying steps between the binding of a signal molecule to a cell surface receptor and the response of the cell. These steps often involve phosphorylation by protein kinases.		6.  How does the binding of a single signal molecule to a cell surface receptor result in an amplified response within the target cell?		•Exploration: Cell-Cell Interactions
7.4 Cell surface proteins mediate cell-cell interactions.
• Cell surface markers, ususally glycolipids, identify a cell as belonging to a specific tissue and MHC proteins on the cell surface identify a cell as "self" or "nonself." • Tight junctions and desmosomes enable cells to adhere in tight, leakproof sheets, holding the cells together such that materials cannot pass between them. • Gap junctions (in animals) and plasmodesmata (in plants) permit small substances to pass directly from cell to cell through special passageways.		7.  What are the functions of tight junctions? What are the functions of desmosomes and adherens junctions, and what proteins are involved in these junctions? 8.  What are the molecular components that make up gap junctions? What sorts of substances can pass through gap junctions? 9.  Where are plasmodesmata found? What cellular constituents are found in plasmodesmata?		•Animal Cell Junctions •Plasmodesmata

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