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Unformatted text preview: Bio2600: Introduction to Cell Biology Study Guide Chapter 16 Answers 16-1 Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by endocrine cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, contact-dependent methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During paracrine signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, neuronal signaling involves the conversion of electrical impulses into a chemical signal. Cells receive signals through a receptor , which can be an integral membrane protein or can reside inside the cell. 16-2 Choice (d) is the correct answer. All members of the steroid hormone receptor family are intracellular proteins (thus choice (a) is not correct) that interact with molecules that can diffuse through the plasma membrane unaided. Steroid hormone receptors shuttle between the cytoplasm and the nucleus, which is why choice (c) is incorrect. They are activated by either steroids or other hydrophobic signaling molecules and typically undergo a large conformational change upon binding to the signaling molecule (choice (b)). This conformational change activates the steroid hormone receptors, allowing them to promote or inhibit the transcription of the appropriate genes. Steroid hormone receptors are important for many aspects of human physiology, including, but not limited to sexual development (choice (e)). 16-3 Since the interactions of the signal molecule with its receptor and of the activated receptor with its gene are both one-to-one, there is no amplification in this part of the signaling pathway. The signal can, however, be amplified when the target gene is transcribed, since multiple copies of mRNA are usually produced from a gene once it has been switched on, and multiple copies of protein can be made from each mRNA molecule. 16-4 (c) 16-5 Ion-channel-linked receptors; G-protein-linked receptors; enzyme-linked receptors. 16-6 Choices (a) and (d) are correct answers. A hydrophilic molecule cannot diffuse across the membrane and can therefore only affect a cell if it binds to a cell-surface receptor that has at least one component that spans the bilayer (choice (a)). Cells having the same set of receptors can respond in different ways to the same ligand molecules, since the response to a receptor also depends on the types of intracellular relay pathways present in the cell (choice (d)). Most signal molecules remain bound to the extracellular domain of the receptor, while the intracellular domain mediates signal transduction. Although many signal molecules are endocytosed with their receptor, they remain inside membrane-...
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- Winter '08
- cell biology