1.
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Molecular biologists believe that signal-transduction pathways evolved early in the history of life because _____. (p. 198)
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| receptor molecules have been identified in preparations of fossil organisms billions of years old |
| simple forms of life, such as prokaryotic cells, utilize cell signaling |
| cell signaling is seen in organisms that do not utilize sexual reproduction |
| the molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago |
| the pathways in primitive organisms, like bacteria, are short, while those in advanced forms, like mammals, are long |
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2.
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A substance that acts at a distance from the site at which it is secreted is classified as a(n) __________. (p. 199)
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| neurotransmitter |
| paracrine signal |
| local regulator |
| hormone |
| synaptic signal |
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3.
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A signal molecule can cause different responses in different cells because _____. (p. 201)
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| different cells possess different enzymes, which modify the signal molecule into different molecules after it has arrived |
| the
transduction process is unique to each cell type; to respond to a
signal, different cells require only a similar membrane receptor |
| different cells have membrane receptors that bind to different sides of the signal molecule |
| the transduction pathway in cells has a variable length |
| all of the above are correct |
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4.
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Cell biologists use the term "ligand" to refer to _____. (p. 201)
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| the target cell of a signal molecule |
| any small molecule that can bind to a larger one |
| the bond that forms between a signal molecule and its receptor |
| the change in shape that occurs when a signal molecule binds to its receptor |
| a molecule that can occupy a receptor site while not activating the receptor |
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5.
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Tyrosine-kinase receptors are characterized by their _____. (p. 203)
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| enzymatic phosphorylation of tyrosine in the receptor protein |
| enzymatic degrading of GTP to GDP |
| allowing specific ions to enter the cell after ligand binding |
| binding to nonpolar signal molecules such as NO or the steroid hormones |
| enzymatic hydrolyzing of the signal molecule shortly after its arrival |
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6.
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When ligand binding results in a change in membrane potential, the receptor type involved must be a(n) _____. (p. 204)
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| ligand-gated ion channel |
| tyrosine-kinase receptor |
| G-protein-linked receptor |
| phosphorylated tyrosine dimer |
| intracellular receptor |
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7.
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Select the correct statement about protein phosphorylation. (p. 205)
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| Phosphorylation always increases the activity of the protein relative to its nonphosphorylated form. |
| Phosphorylation always decreases the activity of the protein relative to its nonphosphorylated form. |
| Protein kinase molecules predominate, causing most inducible pathways to be shut down. |
| Protein phosphatases reverse the effects of phosphorylation by rapidly removing phosphate groups from proteins. |
| Because
phosphate groups are charged, their addition to a protein results in
denaturation as the protein assumes a new tertiary structure. |
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8.
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Two of the most common second messengers are _____. (p. 207)
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| calcium ion and cAMP |
| GTP and GDP |
| kinase and phosphate |
| G proteins and calmodulin |
| kinase and phosphatase |
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9.
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Dioxin,
produced as a by-product of various industrial chemical processes, is
suspected of causing cancer and birth defects in animals and humans. It
apparently acts by entering cells and binding to proteins, altering the
pattern of gene expression. The proteins to which dioxin binds are
likely to be _____. (p. 204)
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| water-soluble proteins |
| DNA polymerase |
| transcription factors |
| enhancers |
| nucleosomes |
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10.
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Why are there often so many steps between the original signal event and the cell's response? (p. 201)
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| Each transduction is a checkpoint, allowing the cell to decide whether to proceed further. |
| Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses. |
| Long,
highly specific pathways minimize the possibility that a relay molecule
could accidentally activate a pathway leading to a secondary response. |
| The accumulation of genetic mutations over time has added redundant steps to the pathway. |
| Lengthy
pathways provide the opportunity for the initial pathway molecules to
recycle back to inactive forms should additional signal molecules be
present. |
