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Chapter 14: Problem 19
What is antisense RNA? How does it affect the translation of a complementary mRNA?
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A species of bacteria can synthesize the amino acid histidine, so they do not require histidine in their growth medium. A key enzyme, which we will call histidine synthetase, is necessary for histidine biosynthesis. When these bacteria are given histidine in their growth medium, they stop synthesizing histidine intracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why histidine biosynthesis ceases when histidine is in the growth medium. To explore this phenomenon further, you measure the amount of intracellular histidine synthetase protein when cells are grown in the presence and absence of histidine. In both conditions, the amount of this protein is identical. Which mechanism of regulation is consistent with this observation?
Mutations may have an effect on the expression of the lac operon and the trp operon. Would the following mutations have a cis- or transeffect on the expression of the protein-encoding genes in the operon? A. A mutation in the operator site that prevents lac repressor from binding to it B. A mutation in the lacI gene that prevents lac repressor from binding to DNA C. A mutation in the \(\operatorname{trp} L\) gene that prevents attenuation
In general, why is it important to regulate genes? Discuss examples of situations in which it would be advantageous for a bacterial cell to regulate genes.
Transcriptional repressor proteins (e.g., lac repressor), antisense RNA, and feedback inhibition are three different mechanisms that turn off the expression of genes and gene products. Which of these three mechanisms will be most effective in each of the following situations? A. Shutting down the synthesis of a polypeptide B. Shutting down the synthesis of mRNA C. Shutting off the function of a protein For your answers to parts \(\mathrm{A}-\mathrm{C}\) that list more than one mechanism, which mechanism will be the fastest or the most efficient?
Some mutations have a cis-effect, whereas others have a transeffect. Explain the molecular differences between cis- and transmutations. Which type of mutation (cis or trans) can be complemented in a merozygote experiment?
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