ch20 - Chapter 20 20.1 Operons are common in bacteria but...

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Chapter 20 20.1 Operons are common in bacteria but not in eukaryotes. Suggest a reason why. ANS: In multicellular eukaryotes, the environment of an individual cell is relatively stable. There is no need to respond quickly to changes in the external environment. In addition, the development of a multicellular organism involves complex regulatory hierarchies composed of hundreds of different genes. The expression of these genes is regulated spatially and temporally, often through intricate intercellular signaling processes. FEEDBACK: 20.6 DIFFICULTY: easy 20.2. In bacteria, translation of an mRNA begins before the synthesis of that mRNA is completed. Why is this “coupling” of transcription and translation not possible in eukaryotes? ANS: Coupling of transcription and translation is not possible in eukaryotes because these two processes take place in different cellular compartments—transcription in the nucleus and translation in the cytoplasm. FEEDBACK: 20.1 DIFFICULTY: easy 20.3 Muscular dystrophy in humans is caused by mutations in an X-linked gene that encodes a protein called dystrophin. What techniques could you use to determine if this gene is active in different types of cells, say skin cells, nerve cells, and muscle cells? ANS: Activity of the dystrophin gene could be assessed by blotting RNA extracted from the different types of cells and hybridizing it with a probe from the gene (northern blotting); or the RNA could be reverse transcribed into cDNA using one or more primers specific to the dystrophin gene and the resulting cDNA could be amplified by the polymerase chain reaction (RT-PCR). Another technique would be to hybridize dystrophin RNA in situ —that is, in the cells themselves—with a probe from the gene. It would also be possible to check each cell type for production of dystrophin protein by using anti-Dystrophin antibodies to analyze proteins from the different cell types on
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western blots, or to analyze the proteins in the cells themselves—that is, in situ . FEEDBACK: 20.1 DIFFICULTY: medium 20.4. Why do steroid hormones interact with receptors inside the cell, whereas peptide hormones interact with receptors on the cell surface? ANS: Steroid hormones are small, lipid-soluble molecules that have little difficulty passing through the cell membrane. Peptide hormones are typically too large to pass through the cell membrane freely; rather, their influence must be mediated by a signaling system that begins with a membrane-bound receptor protein that binds the hormone. FEEDBACK: 20.1 DIFFICULTY: easy 20.5 How could you use the polytene chromosomes of Dipteran insects to study the regulation of transcription? ANS: By monitoring puffs in response to environmental signals, such as heat shock, or to hormonal signals. FEEDBACK:
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ch20 - Chapter 20 20.1 Operons are common in bacteria but...

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