Freeman 8th EditionCh. 16+17 - Transcription, RNA Processing, and TranslationProblem 13Chapter 16, Problem 13
Toxins like αα-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of αα-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of αα-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with αα-amanitin will have a reduced level of: a. tRNAs b. rRNAs c. snRNAs d. mRNAs
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Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called αα-amanitin, a toxin that inhibits transcription.What would you predict to be the immediate outcome of adding αα-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 rate of translocation of ribosomes translating mRNA
Investigators examined the expression of transporter mRNA and protein produced in zebrafish homozygous for each of the alleles and obtained the results summarized here (+ = present, −= absent). Does the allele associated with light color appear to be altering transcription or translation? Why?
α-Amanitin inhibits transcription by binding inside an RNA polymerase to a region other than the active site that catalyzes addition of a nucleotide to the RNA chain. Based on the model of RNA polymerase shown in Figure 17.3, predict how the toxin might function to inhibit transcription.
A small portion of the human transport protein amino acid sequence is shown here. The upper sequence is associated with darker skin, and the lower sequence is associated with lighter skin. What DNA base-pair change created the light-skin form of the human protein from the gene that coded for the dark-skin form?
Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.
If you wanted to use αα-amanitin to shut down 95 percent of transcription by RNA polymerase II, roughly what concentration of αα-amanitin would you use? Note that the scale on the x-axis of the graph in Question 13 is logarithmic rather than linear, so that each tick mark shows a tenfold higher concentration.