C14 - C1. A constitutive gene is unregulated, which means...

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C1. A constitutive gene is unregulated, which means that its expression level is relatively constant. The expression of a regulated gene varies under different conditions. In bacteria, the regulation of genes oftentimes occurs at the level of transcription by combinations of regulatory proteins and small effector molecules. In addition, gene expression can be regulated at the level of translation or the function of a protein can be regulated after translation is completed. C2. In bacteria, gene regulation greatly enhances the efficiency of cell growth. It takes a lot of energy to transcribe and translate genes. Therefore, a cell is much more efficient and better at competing in its environment if it expresses genes only when the gene product is needed. For example, a bacterium will express only the genes that are necessary for lactose metabolism when a bacterium is exposed to lactose. When the environment is missing lactose, these genes are turned off. Similarly, when tryptophan levels are high within the cytoplasm, the genes that are required for tryptophan biosynthesis are repressed. C3. In this case, an activator protein and inhibitor molecule are involved. The binding of the inhibitor molecule to the activator protein would prevent it from binding to the DNA and thereby inhibit its ability to activate transcription. C4. A. Regulatory protein B. Effector molecule C. DNA segment D. Effector molecule E. Regulatory protein F. DNA segment G. Effector molecule C5. Choices B and C are correct. In both of these cases, the presence of the small effector molecule will turn off transcription. In contrast, the presence of an inducer turns on transcription. C6. A cis -mutation is within a genetic regulatory sequence, such as an operator site, that affects the binding of a genetic regulatory protein. A cis -mutation affects only the adjacent genes that the genetic regulatory sequence controls. A trans -mutation is usually in a gene that encodes a genetic regulatory protein. A trans -mutation can be complemented in a merozygote experiment by the introduction of a normal gene that encodes the regulatory protein. C7. The term enzyme adaptation means that a particular enzyme is made only when a cell is exposed to the substrate for that enzyme. It occurs because the gene that encodes the enzyme that is involved in the metabolism of the substrate is expressed only when the cells have been exposed to the substrate. C8. A. No transcription would take place. The lac operon could not be expressed. B. No regulation would take place. The operon would be continuously turned on. C. The rest of the operon would function normally but none of the transacetylase would be made. C9. It would be impossible to turn the lac operon on even in the presence of lactose because the repressor protein would remain bound to the operator site. C10. Diauxic growth refers to the phenomenon whereby a cell first uses up one type of sugar (e.g., glucose) before it
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C14 - C1. A constitutive gene is unregulated, which means...

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