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Ch. 16+17 - Transcription, RNA Processing, and Translation
All textbooksFreeman 8th EditionCh. 16+17 - Transcription, RNA Processing, and TranslationProblem 13
Chapter 16, Problem 13

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?

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1
Compare the amino acid sequences of the two proteins. Identify the position where the sequences differ.
Note that the third amino acid in the upper sequence is Ala (Alanine) and in the lower sequence is Thr (Threonine).
Determine the codons for Alanine (Ala) and Threonine (Thr). Alanine is coded by GCU, GCC, GCA, or GCG. Threonine is coded by ACU, ACC, ACA, or ACG.
Identify the specific codon change that could result in the amino acid change from Alanine to Threonine. For example, GCU (Alanine) could change to ACU (Threonine).
Conclude that the DNA base-pair change responsible for the amino acid change is a mutation in the codon from GCU to ACU.

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Related Practice
Textbook Question

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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Textbook Question

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.

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Textbook Question

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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Textbook Question

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.

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Textbook Question

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.

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Textbook Question

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 is addition of a toxin important in this study?

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