Concepts of Genetics (12th Edition)
12th Edition
ISBN: 9780134604718
Author: William S. Klug, Michael R. Cummings, Charlotte A. Spencer, Michael A. Palladino, Darrell Killian
Publisher: PEARSON
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Chapter 13, Problem 23PDQ
One form of posttranscriptional modification of most eukaryotic pre-mRNAs is the addition of a poly-A sequence at the 3′ end. The absence of a poly-A sequence leads to rapid degradation of the transcript. Poly-A sequences of various lengths are also added to many bacterial RNA transcripts where, instead of promoting stability, they enhance degradation. In both cases, RNA secondary structures, stabilizing proteins, or degrading enzymes interact with poly-A sequences. Considering the activities of RNAs, what might be general functions of 3′-polyadenylation?
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As described earlier, DNA damage can cause deletion or insertion of base pairs. If a nucleotide base sequence of a coding region changes by any number of bases other than three base pairs, or multiples of 3, a frameshift mutation occurs. Depending on the location of the sequence change, such mutations can have serious effects. The following synthetic mRNA sequence codes for the beginning of a polypeptide: 5′-AUGUCUCCUACUGCUGACGAGGGAAGGAGGUGGCUUAUC-AUGUUU-3′ First, determine the amino acid sequence of the polypeptide. Then determine the types of mutation that have occurred in the following altered mRNA segments. What effect do these mutations have on the polypeptide products? a. 5′-AUGUCUCCUACUUGCUGACGAGGGAAGGAGGUGGCUUAUCA-UGUUU-3′ b. 5′-AUGUCUCCUACUGCUGACGAGGGAGGAGGUGGCUUAUCAU-GUUU-3′ c. 5′-AUGUCUCCUACUGCUGACGAGGGAAGGAGGUGGCCCUUAUC-AUGUUU-3′ d. 5′-AUGUCUCCUACUGCUGACGGAAGGAGGUGGCUUAUCAU-GUUU-3′
A common feature of many eukaryotic mRNAs is the presence of a rather long 3′ UTR, which often contains consensus sequences. Creatine kinase B (CK-B) is an important enzyme in cellular metabolism. Certain cells—termed U937D cells—have lots of CK-B mRNA, but no CK-B enzyme is present. In these cells, the 5′ end of the CK-B mRNA is bound to ribosomes, but the mRNA is apparently not translated. Something inhibits the translation of the CK-B mRNA in these cells. Researchers introduced numerous short segments of RNA containing only 3′ UTR sequences into U937D cells. As a result, the U937D cells began to synthesize the CK-B enzyme, but the total amount of CK-B mRNA did not increase. The introduction of short segments of other RNA sequences did not stimulate the synthesis of CK-B; only the 3′ UTR sequences turned on the translation of the enzyme. On the basis of these results, propose a mechanism for the inhibition of CK-B translation in the U937D cells. Explain how the introduction of short…
Once a primary RNA transcript is created from a DNA template, it must be modified in
several ways before becoming messenger RNA (mRNA), ribosomal RNA (rRNA) or
transfer RNA (TRNA). The following image shows RNA processing of one pre-mRNA
into mRNA. Note that pre-RNA is processed in three ways: 1) a 5' methylguanylate cap
(G cap) is added, 2) a poly-A tail is added, and 3) the spliceosome removes introns from
the pre-mRNA transcript. Please redraw the following diagram and label the following
on your diagram:
DNA
Promoter
pre-mRNA
(unprocessed)
mRNA
*5' methylguanylate cap
*polyadenylation
*Exon (may be more than one)
*Intron (may be more than one)
Transcription
RNA processing
AAAAA
PART C: FOLLOW-UP QUESTIONS
1. Why is a poly-A tail important?:
2. What do introns do? Why do they exist in eukaryotes when they are mostly
absent in prokaryotes?
3. What do you think 'alternative splicing' means, and how might it expand the
function of a gene?
Chapter 13 Solutions
Concepts of Genetics (12th Edition)
Ch. 13 - In a mixed heteropolymer experiment using...Ch. 13 - When repeating copolymers are used to form...Ch. 13 - The following represent deoxyribonucleotide...Ch. 13 - Prob. 1CSCh. 13 - A 30-year-old woman was undergoing therapy for...Ch. 13 - A 30-year-old woman was undergoing therapy for...Ch. 13 - HOW DO WE KNOW? In this chapter, we focused on the...Ch. 13 - CONCEPT QUESTION Review the Chapter Concepts list...Ch. 13 - Assuming the genetic code is a triplet, what...Ch. 13 - The mRNA formed from the repeating tetranucleotide...
Ch. 13 - In studies using repeating copolymers, AC ......Ch. 13 - In a coding experiment using repeating copolymers...Ch. 13 - Prob. 7PDQCh. 13 - When the amino acid sequences of insulin isolated...Ch. 13 - Prob. 9PDQCh. 13 - Why doesnt polynucleotide phosphorylase (Ochoas...Ch. 13 - Refer to Table 13.1. Can you hypothesize why a...Ch. 13 - Predict the amino acid sequence produced during...Ch. 13 - A short RNA molecule was isolated that...Ch. 13 - A glycine residue is in position 210 of the...Ch. 13 - Refer to Figure 13.7 to respond to the following:...Ch. 13 - Most proteins have more leucine than histidine...Ch. 13 - Define the process of transcription. Where does...Ch. 13 - Prob. 18PDQCh. 13 - Describe the structure of RNA polymerase in...Ch. 13 - Prob. 20PDQCh. 13 - Messenger RNA molecules are very difficult to...Ch. 13 - Present an overview of various forms of...Ch. 13 - One form of posttranscriptional modification of...Ch. 13 - Describe the role of two forms of RNA editing that...Ch. 13 - Substitution RNA editing is known to involve...Ch. 13 - Prob. 26ESPCh. 13 - Prob. 27ESPCh. 13 - Prob. 28ESPCh. 13 - Shown here are the amino acid sequences of the...Ch. 13 - The genetic code is degenerate. Amino acids are...Ch. 13 - M. Klemke et al. (2001) discovered an interesting...Ch. 13 - Recent observations indicate that alternative...Ch. 13 - Isoginkgetin is a cell-permeable chemical isolated...
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- Once a primary RNA transcript is created from a DNA template, it must be modified in several ways before becoming messenger RNA (mRNA), ribosomal RNA (rRNA) or transfer RNA (tRNA). The following image shows RNA processing of one pre-mRNA into mRNA. Note that pre-RNA is processed in three ways: 1) a 5' methylguanylate cap (G cap) is added, 2) a poly-A tail is added, and 3) the spliceosome removes introns from the pre-mRNA transcript. Please redraw the following diagram and label the following on your diagram: DNA Promoter pre-mRNA (unprocessed) mRNA *5' methylguanylate cap *polyadenylation *Exon (may be more than one) *Intron (may be more than one) Transcription RNA processing AAAAAarrow_forwardThe deadenylation pathway is a critical means of maintaining a steady state level of mRNAs and proteins in the cells. How does deadenylation affect protein synthesis if it works on mRNAs? Options: loss of the poly A tail results in rapid 3'-5' degradation of transcript leading to reduced protein synthesis deadenylation can result in an increased exposure of the cap to enzymes involved in decapping, leading to subsequent 5' mediated degradation it reduces the ability of mRNAs to form 5' 3' circular mRNA structures that protects both termini a and b only a, b and carrow_forwardKnowing that the genetic code is almost universal, a scientist uses molecular biological methods to insert the human β-globin gene (Shown in Figure 17.11) into bacterial cells, hoping the cells will express it and synthesize functional β-globin protein. Instead, the protein produced is nonfunctional and is found to contain many fewer amino acids than does β-globin made by a eukaryotic cell. Explain why.arrow_forward
- For a specific type of mutation at a given location in a particular gene, identify whether it will affect the size of the mRNA, the protein, or both. How would the mutant appear on a gel in comparison to the originalarrow_forwardIn eukaryotes there is not a consistent relationship between the length of the coding sequence of a gene and the length of the mature mRNA it encodes, even though one nucleotide in DNA = one nucleotide in pre-mRNA or primary transcript. Explain why this is so.arrow_forwardThe following four mutations have been discovered in a gene that has more than 60 exons and encodes a very large protein of 2532 amino acids. Indicate which mutation would likely cause a detectable change in the size of the mRNA and/or the size of the protein product. Consider a detectable change to be >10% of the wild-type size. A table of the genetic code is shown below. First letter 0 00 U O A บบบ UUC UUA UUG U CUU CUC CUA CUG Phe GUU GUC GUA GUG Leu >Leu AUU AUC lle AUA AUG Met >Val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG Second letter C Ser Pro Thr Ala CAU CAC CAA CAG UAU UGU Tyr UAC UGC UAA Stop UGA UAG Stop UGG AAU AAC AAA AAG A GAU GAC GAA GAG His Gin Asn Lys Asp G Glu CGU CGC CGA CGGJ AGU AGC AGA AGG GGU GGC GGA GGG O AAG576UAG (changes codon 576 from AAG to UAG) Cys Stop Trp O GUG326AUG (changes codon 326 from GUG to AUG) Arg Ser Arg Gly DUAG DUA G DCAG DO AG deletion of codon 779 insertion of 1000 base pairs into the sixth intron (this particular…arrow_forward
- The primary RNA transcript of the chicken ovalbumin gene is 7700 nucleotides long, but the mature mRNA that is translated on the ribosome is 1872 nucleotides long. This size difference occurs primarily as a result of: capping cleavage of polycistronic mRNA removal of poly A tails reverse transcription splicingarrow_forwardHelp me pleasearrow_forward) A normal mRNA that reads 5'- UGCCAUGGUAAUAACACAUGAAGGCCUGAAC-3' was an insertion mutation that changes the sequence to 5'- UGCCAUGGUUAAUAACACAUGAGGCGUGAAC-3'. Translate the original mRNA and the mutated mRNA and explain how insertion mutations can have dramatic effects on proteins. ( Hint; Be sure to find the initiation site).arrow_forward
- One of the challenges of studying RNA is the rapid degeneration of RNA. While the half-life of mRNA depends on the solutionit is in, in situ the half life of mRNA is between 5 minutes (E. coli) and 25 minutes (S. cerevisiae). When performing gene expression analyses it is important to make sure you can freeze a sample of mRNA in liquid nitrogen (halting mRNA decay) rapidly as to not loose too much of the original expression. Answer question A and B in order to answer the attached image questions Poll 1 and 2. A. You are doing an experiment with E. coli, what is the decay mRNA decay rate? B. If the sample initially has 0.25 pico-moles or mRNA, how much will remain in the sample if you freeze it 3 minutes later? See attached image for next question. Answer the two green poll questions please!!arrow_forwardThe most common type of termination signal in E. Coli is a symmetrical inverted repeat of GC rich sequences followed by about 7 As that forms a stable stem-loop structure in the RNA, which disrupts its association with the DNA template and terminates transcription. true or falsearrow_forwardOne procedure of obtaining cDNA from mRNA is by using oligo(dT) primers. What are oligo(dT)s? Why does using them make sense based on the processing (or modification) of precursor mRNA to get mature mRNA?arrow_forward
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