MASTERING BIOLOGY CHP 17 Transcription and Translation

After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?

1. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. 2. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. 3. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.

Which one of the following statements about RNA processing is true? A. Exons are cut out before mRNA leaves the nucleus. B. Ribozymes may function in RNA splicing. C. A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus. D. RNA splicing can be catalyzed by tRNA.

B. Ribozymes may function in RNA splicing.

In eukaryotes, when mature mRNA is hybridized to complementary DNA, ______. A. exons loop out as single-stranded regions of DNA B. introns loop out as single-stranded regions of DNA C. introns loop out as single-stranded regions of RNA D. exons loop out as single-stranded regions of RNA

B. introns loop out as single-stranded regions of DNA These regions are transcribed but are removed from the RNA by splicing.

Which statement is most accurate concerning the function(s) of the 5' cap and the 3' poly(A) tail of eukaryotic mRNAs? A. The poly(A) tail stabilizes the mRNA, but plays no direct role in its translation to protein. B. The 5' cap is important for initiating translation but plays no role in stabilizing mRNA. C. Neither structure has any known function. D. Both structures are important for initiating translation and extending the lifespan of the mRNA.

D. Both structures are important for initiating translation and extending the lifespan of the mRNA.

During mRNA splicing ______. A. RNAs within the ribosome recognize and remove exons B. snRNPs that make up the spliceosome recognize and remove exons C. RNAs within the ribosome recognize and remove introns D. snRNPs that make up the spliceosome recognize and remove introns

D. snRNPs that make up the spliceosome recognize and remove introns. The finished mRNA contains an uninterrupted message.

During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand?

The base sequence of the gene's promoter In eukaryotes, binding of RNA polymerase II to DNA involves several other proteins known as transcription factors. Many of these transcription factors bind to the DNA in the promoter region, located at the 3' end of the sequence on the template strand. Although some transcription factors bind to both strands of the DNA, others bind specifically to only one of the strands. Transcription factors do not bind randomly to the DNA. Information about where each transcription factor binds originates in the base sequence to which each transcription factor binds. The positioning of the transcription factors in the promoter region determines how the RNA polymerase II binds to the DNA and in which direction transcription will occur.

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its 5' cap and poly-A tail. Which of the following would you expect her to find?

The molecule is digested by enzymes because it is not protected at the 5' end.

A ribozyme is _____.

an RNA with catalytic activity