Choose the ONE best answer.
1.1. An 8-month-old male with severe anemia is found to have β-thalassemia. Genetic analysis shows that one of his β-globin genes has a mutation that creates a new splice-acceptor site 19 nucleotides upstream of the normal splice-acceptor site of the first intron. Which of the following best describes the new messenger RNA molecule that can be produced from this mutant gene?
A. Exon 1 will be too short.
B. Exon 1 will be too long.
C. Exon 2 will be too short.
D. Exon 2 will be too long.
E. Exon 2 will be missing.
Correct answer = D. Because the mutation creates an additional splice-acceptor site (the 3′-end) upstream of the normal acceptor site of intron 1, the 19 nucleotides that are usually found at the 3′-end of the excised intron 1 lariat can remain behind as part of exon 2. The presence of these extra nucleotides in the coding region of the mutant messenger RNA (mRNA) molecule will prevent the ribosome from translating the message into a normal β-globin protein molecule. Those mRNA for which the normal splice site is used to remove the first intron will be normal, and their translation will produce normal β-globin protein.
1.2. A 4-year-old child who easily tires and has trouble walking is diagnosed with Duchenne muscular dystrophy, an X-linked recessive disorder. Genetic analysis shows that the patient’s gene for the muscle protein dystrophin contains a mutation in its promoter region. Of the choices listed, which would be the most likely effect of this mutation?
A. Initiation of dystrophin transcription will be defective.
B. Termination of dystrophin transcription will be defective.
C. Capping of dystrophin messenger RNA will be defective.
D. Splicing of dystrophin messenger RNA will be defective.
E. Tailing of dystrophin messenger RNA will be defective.
Correct answer = A. Mutations in the promoter typically prevent formation of the RNA polymerase II transcription initiation complex, resulting in a decrease in the initiation of messenger RNA (mRNA) synthesis. A deficiency of dystrophin mRNA will result in a deficiency in the production of the dystrophin protein. Capping, splicing, and tailing defects are not a consequence of promoter mutations. They can, however, result in mRNA with decreased stability (capping and tailing defects) or an mRNA in which exons have been skipped (lost) or introns retained (splicing defects).
1.3. A mutation to this sequence in eukaryotic messenger RNA (mRNA) will affect the process by which the 3′-end polyadenylate (poly-A) tail is added to the mRNA.
A. AAUAAA
B. CAAT
C. CCA
D. GU… A…AG
E. TATAAA
Correct answer = A. An endonuclease cleaves mRNA just downstream of this polyadenylation signal, creating a new 3′-end to which polyadenylate polymerase adds the poly-A tail using ATP as the substrate in a template-independent process. CAAT and TATAAA are sequences found in promoters for RNA polymerase II. CCA is added to the 3′-end of pre-transfer RNA by nucleotidyltransferase. GU…A…AG denotes an intron in eukaryotic premRNA.
1.4. This protein factor identifies the promoter of protein-coding genes in eukaryotes.
A. Pribnow box
B. Rho
C. Sigma
D. TFIID E. U1
Correct answer = D. The general transcription factor TFIID recognizes and binds core promoter elements such as the TATA-like box in eukaryotic protein-coding genes. These genes are transcribed by RNA polymerase II. The