Scott Freeman
Biological Science 2e
PRENTICE HALL 2005 ISBN: 0-13-140941-7
Classroom Response System - Questions
Using the information below, answer the following two questions.
It has been estimated that approximately half of human genes yield mRNAs of different sequences because the splicing of introns can vary among different tissues and cellular circumstances. Consider what would be the consequence of splicing RNAs in different ways; different proteins would be produced from the same gene. Such a condition would be a direct challenge to Beadle and Tatum’s one gene one enzyme hypothesis. Interestingly, the condition in mice called“quaking”, is caused by a recessive dysmyelination mutation (qk) which appears to involve defects in the way in which initial mRNAs are spliced. Homozygotes (qk/qk)suffer tremors during exertion. Below is a figure that describes the splicing patterns in various genotypes of quaking and normal mice. Portions of brain MAG (myelin associated glycoprotein) mRNA (including exons 11, 12 and 13) from young (14 day) and adult (2 month) mice are represented. The relative concentration of each RNA is indicated in the gel diagram by the density of the bands. Figure and data are modified from Wu, J. et al. 2002. PNAS 99:4233-4238. Exons are represented by boxes.
A = +/qk youngB = qk/qk young
C = +/qk adultD = qk/qk adult
1) With respect to age (young vs. adult), what two general patterns of RNA splicing are apparent?
A. Young mice appear to generate mRNAs with and without exon 12 while adult mice preferentially generate mRNAs which contain exon 12.
B. Young mice appear to generate mRNAs without exon 12 while adult mice preferentially generate mRNAs which contain exons 12 and 13.
C. Young and old mice generate mRNAs in identical fashion.
Question Type: Conceptual/Applied
Question Skill/Objective: Data interpretation
Difficulty level: High
Section Reference: 16.2
Source/Suggested Use: In Class
Notes: It might be necessary to review the technique of gel electrophoresis, then go over the results of this type of experiment.
2) With respect to genotype (+/qk vs. qk/qk), what two general patterns of RNA splicing are apparent?
A. Young mice which are +/qk produce more mRNAs which contain exon 12 than do young mice which are qk/qk. Genotype does not appear to influence the pattern of splicing in adult mice.
B. Adult mice which are qk/qk produce more mRNAs which contain exon 12 than do adult mice which are +/qk. Genotype does not appear to influence the pattern of splicing in young mice.
C. Young mice which are qk/qk produce more mRNAs which contain exon 12 than do young mice which are +/qk. Genotype does not appear to influence the pattern of splicing in adult mice.
Question Type: Conceptual/Applied
Question Skill/Objective: Data interpretation
Difficulty level: High
Section Reference: 16.2
Source/Suggested Use: In Class
Notes: It might be necessary to review the technique of gel electrophoresis, then go over the results of this type of experiment.
3) It has been estimated that approximately half of human genes yield mRNAs of different sequences because the splicing of introns can vary among different tissues and cellular circumstances. Consider what would be the consequence of splicing RNAs in different ways; different proteins would be produced from the same gene. Such a condition would be a direct challenge to Beadle and Tatum’s one gene one enzyme hypothesis. In addition to alternative splicing as described above, incorrectly spliced RNAs lead to human pathologies. Xu and Lee (2003. Nucleic Acids Research 31:5635-5643) examined human cancers for splice-specific changes and found that many of the changes disrupted tumor suppressor function, that is, gene products which control the mitotic cell cycle. What types of RNAs would be probably not be expected when there is a loss of splicing specificity?
A. a variety of non-specific variants producing RNA pools with many lengths and combinations of exons and introns
B. incomplete splicing where introns and exons are erroneously included or excluded in the mRNA product
C. a variety of nonsense products which result in premature RNA decay or truncated protein (shorter than usual) products
D. RNA pools which are extremely homogeneous and produce only a single wild type protein.
Question Type: Conceptual/Applied
Question Skill/Objective: Data interpretation
Difficulty level: High
Section Reference: 16.2
Source/Suggested Use: In Class
Notes: This question should be discussed at some length. It is important that students understand that various splicing possibilities occur naturally and that sometimes improper splicing leads to abnormal phenotypes. Notice that the introduction to this question is the same as in the previous question so that either question can stand alone.
4)If one compares the base sequences of related genes from different but closely related species one is likely to find that corresponding ______are usually conserved but the sequences of ______are much less well conserved.
A. exons; introns
B. introns; exons
C. introns; chaperons
D. chaperons; exons
E. introns; proteins
Question Type: Conceptual/Applied
Question Skill/Objective: General
Difficulty level: Low
Section Reference: 16.2
Source/Suggested Use: Exam or in class
Notes: This question would be useful in a class discussion. It would help students see that introns are much less subject to selective pressure than exons generally.
5) Select three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes.
A. 5'-capping, 3'-poly(A) tail addition, splicing
B. 3'-capping, 5'-poly(A) tail addition, splicing
C. removal of exons, insertion of introns, capping
D. 5’-poly(A) tail addition, insertion of introns, capping
E. heteroduplex formation, base modification, capping
Question Type: Conceptual/Applied
Question Skill/Objective: General
Difficulty level: Moderate
Section Reference: 16.2
Source/Suggested Use: Exam or in class
Notes: It might be helpful to summarize this information for the students in classroom discussion.