Chapter 17

What does a bacterial RNA polymerase produce when it transcribes a protein- coding gene? a. rRNA b. tRNA c. mRNA d. snRNA

Where is the start codon located? a. at the very start ( \(5^{\prime}\) end) of the mRNA b. in the DNA just upstream of where transcription starts c. at the downstream end of the \(5^{\prime}\) untranslated region (UTR) d. at the upstream end of the \(3^{\prime}\) untranslated region (UTR)

Splicing begins: a. as transcription occurs. b. after transcription is complete. c. as translation occurs. d. after translation is complete.

Compared with mRNAs that have a cap and tail, predict what will be observed when a eukaryotic mRNA lacks a cap and poly(A) tail. a. The primary transcript cannot be processed properly. b. Translation occurs inefficiently. c. Enzymes on the ribosome add back a cap and poly(A) tail. d. tRNAs become resistant to degradation (being broken down).

RNases and proteases are enzymes that destroy RNAs and proteins, respectively. Which of the following enzymes when added to a spliceosome is predicted to prevent recognition of pre-mRNA regions critical for splicing? a. an RNase specific for tRNAs b. an RNase specific for snRNAs c. a protease specific for initiation factors d. a protease specific for a release factor

A friend argues that redundancy of the genetic code (see Chapter 16 ) is due to wobble pairing. Explain why this isn't the case.

Temperature-sensitive conditional mutations cause expression of a wild-type phenotype at one growth temperature and a mutant phenotype at another- typically higher-temperature. Imagine that when a bacterial cell carrying such a mutation is shifted from low to high growth temperatures, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects what feature? a. the terminator sequence b. the start codon \(\mathbf{c} .\) sigma d. one of the polypeptides of the core RNA polymerase

In what ways are a promoter and a start codon similar? In what ways are they different?

What would you predict to be the immediate outcome of adding \(\alpha\) -amanitin to a cell? a. reduced DNA synthesis b. reduced production of one or more types of RNA c. reduced binding of tRNAs to anticodons d. reduced activity of ribosomes translating mRNA

Toxins like \(\alpha\) -amanitin are used for research in much the same way as null mutants (see Chapter 16 )-to disrupt a process and see what happens when it no longer works. Researchers examined the ability of \(\alpha\) -amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of \(\alpha\) -amanitin, and then tested their activity. The results of this experiment are shown below. These findings suggest that \(\alpha\) -amanitin- treated cells will have reduced levels of: a. tRNAs b. rRNAs c. snRNAs d. mRNAs

Biologists have investigated how fast pre-mRNA splicing occurs by treating cells with a toxin that blocks the production of new pre-mRNAs, then following the rate of splicing of the pre-mRNAs that were transcribed before adding the toxin. Why was addition of a toxin important in this study?

The primary cause of death from \alpha-amanitin poisoning is liver failure. Suppose a physician informs you that the liver cells die because their rate of protein production falls below a level needed to maintain active metabolism. Given that \(\alpha\) -amanitin is an inhibitor of transcription, you wonder if this information is correct. Propose an experiment to determine whether the toxin also has an effect on protein synthesis.