 |  Biology, 6/e Author Dr. George B. Johnson,
Washington University
Author Dr. Peter H. Raven,
Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer,
Carleton College
Contributor Dr. Jonathan Losos,
Washington University
Control of Gene Expression
Answers to Review Questions|
Chapter 16 (p. 330)
1. Using various binding motifs, regulatory proteins can bind to the outside surface of DNA where base pairs are exposed within the major groove.
2. A helix-turn-helix is a regulatory protein consisting of two a-helices joined by a short non-helical segment. It fits into the major groove of the DNA. Homeodomains function during the development of the organism as "developmental switches," and are critical in how different body regions are assembled.
3. When bacteria are grown in a medium containing tryptophan, they do not need to manufacture the amino acid, so their trp gene is inhibited by a repressor, which binds to the trp promoter. In the absence of tryptophan, the repressor protein is not triggered, does not bind to the promoter, and transcription of the trp gene occurs, supplying the amino acid to the bacterium.
4. When lactose is present in the environment, a lactose isomer binds to the lac repressor removing it from its regulatory position on the DNA and permitting transcription of the lac gene to occur.
5. Eukaryotic transcription factors stabilize and guide RNA polymerase. Enhancers in eukaryotic cells permit regulation of transcription from a distance, often a considerable distance, whereas bacterial regulation occurs directly at the site of the gene.
6. Methylation blocks the transcription of "turned off" genes, seeing to it that they stay turned off.
7. The primary RNA transcript contains both introns and exons. Primary transcripts undergo processing prior to leaving the nucleus, during which the noncoding introns are removed.
8. The cells can modify some of the transcription factors or they may use translation repressor proteins.
|
|
2002 McGraw-Hill Higher Education