Freeman 8th EditionCh. 16+17 - Transcription, RNA Processing, and TranslationProblem 12Chapter 16, Problem 12
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?
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Controlling the rates of transcription and translation is important in bacteria to avoid collisions between ribosomes and RNA polymerases. Calculate what the maximum rate of translation by a ribosome in a bacterial cell would have to be, in units of amino acids per second, so as not to overtake an RNA polymerase that is synthesizing mRNA at a rate of 60 nucleotides per second. How long would it take for this bacterial cell to translate an mRNA containing 1800 codons?
Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele? a. a missense mutation b. a frameshift mutation c. a neutral mutation d. a silent mutation
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
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.
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
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?