Gccggaaugcugcuggc

aspartic acid threonine leucine glycine alanine cysteine leucine methionine

6. Allolactose induces the lac regulon by binding to a(n)... A. operator. B. repressor.

C. activator. D. CAP protein.

7. Under which of the following conditions will transcription of the lac operon occur?

A. Lactose present/glucose present

B. Lactose present/glucose absent

C. Lactose absent/glucose present

D. Lactose absent/glucose absent

8. Which of the following statements about gene expression is false?

A. More than one RNA polymerase can be transcribing a specific gene at a given time.

B. More than one ribosome can be translating a specific transcript at a given time.

C. Translation begins at a site called a promoter.

D. Transcription stops at a site called a terminator.

E. Some amino acids are coded for by more than one codon.

9. Which of the following is not characteristic of eukaryotic gene expression?

C. Introns must be removed to create the mRNA that is translated.

D. The mRNA is often polycistronic.

E. Translation begins at the first AUG.

10. Which of the following statements is false?

A. A derivative of lactose serves as an inducer of the lac operon.

B. Signal transduction provides a mechanism for a cell to sense the conditions of its external environment.

C. The function of homoserine lactone is to enable a cell to sense the density of like cells.

D. An example of a two-component regulatory system is the lactose operon, which is controlled by a repressor and an activator.

E. An ORF is a stretch of DNA that may encode a protein.

190 Chapter 7 The Blueprint of Life, from DNA to Protein Applications

1. A graduate student is trying to isolate the gene coding for an enzyme found in a species of Pseudomonas that degrades trinitrotoluene (TNT). The student is frustrated to find that the organism does not produce the enzyme when grown in nutrient broth, making it is difficult to collect the mRNA needed to help identify the gene. What could the student do to potentially increase the amount of the desired enzyme?

2. A student wants to remove the introns from a segment of DNA coding for protein X. Devise a strategy for how this could be accomplished.

Critical Thinking

1. The study of protein synthesis often uses a cell-free system where cells are ground with an abrasive to release the cell contents and then filtered to remove the abrasive. These materials are added to the system, generating the indicated results: Materials Added Results

Radioactive amino acids Radioactive protein produced Radioactive amino acids No radioactive protein produced and RNase

(an RNA-digesting enzyme)

What is the best interpretation of these observations?

2. In a variation of the experiment in the previous question, the following materials were added to three separate cell-free systems, generating the indicated results:

Results

Radioactive protein produced Radioactive protein produced

Materials Added

Radioactive amino acids Radioactive amino acids and DNase

(a DNA-digesting enzyme)

Several hours after grinding: No radioactive protein produced Radioactive amino acids and DNase

What is the best interpretation of these observations?

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