Chapter 13: Transcription and Translation

1.	The 5' cap and poly (A) tail that are attached to eukaryotic mRNAs appear to help the message last longer by protecting it from degradation by RNases. But why is an enzyme like RNase in the cell in the first place? What function would an enzyme that destroys messages serve?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2.	Pribnow let RNA polymerase and DNA react before treatment with the DNase enzyme, and then recovered fragments of DNA about 50 nucleotides long. He also did an experiment in which polymerase was omitted at the first step. In this treatment no DNA fragments were obtained. In what sense does this second experiment serve as a control for the first experiment?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3.	Look back at Figure 13.1, which shows the formation of a phosphodiester bond during RNA polymerization. Then study the structure of the nucleotide shown here, called cordycepin. If cordycepin is added to cell-free transcription reaction, it is added onto the growing RNA chain. This observation confirms that synthesis occurs by addition of monomers in the form of triphosphates to the 3' end of the growing chain. Briefly explain why. Be sure to describe the expected result if synthesis occurred at the 5' end of the polymer.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
4.	Carl Woese has determined the nucleotide sequence of rRNA molecules from a diverse array of organisms and compared them with each other. According to his data, certain portions of the rRNAs in the large subunit are very similar in all organisms. To make sense of this result, Woese suggests that the conserved sequences have an important functional role. His logic is that the conserved sequences are so important to cell function that any changes in the sequence cause death. Woese also claims that the existence of the conserved sequences supports other data indicating that peptide bond formation is catalyzed by the large rRNA. Explain the thinking behind his claim.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.