This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Alternative Splicing Produces Multiple Forms of RNA”.
1. How many types of specific domains are present in the SR protein?
Explanation: The SR protein has 2 special RNA binding domains. They are RNA-recognition motif (RRM) and the other is RS domain.
2. Which of the following components of the splicosome machinery is recruited by the SR protein?
Explanation: The SR proteins help efficient recruitment of the components to the different splicosome components to the nearby splice site. Specifically the SR proteins recruit the U2AF proteins to the 3’ splice site and U1 to the 5’ splice site.
3. SR proteins are not essential for RNA splicing.
Explanation: SR proteins are essential for RNA splicing. They not only ensure the accuracy and efficiency of constitutive splicing but also regulate alternative splicing. They come in many varieties, some controlled by physiological signals, others constitutively active.
4. The presence and activity of SR determines the ___________
a) Product formed after splicing
b) Mechanism of splicing
c) Usage of particular splice site
d) Repression of splicing mechanism
Explanation: The SR family protein is large and diverse that has specific roles in regulated alternative splicing by directing the splicing machinery to different splice sites under different conditions. Thus, the presence of activity of a given SR protein can determine whether a particular splice site is used in a particular cell type, or at a particular stage of development.
5. Alternative splicing is regulated by activators and repressors.
Explanation: Proteins that regulate splicing bind to the specific sites called exonic or intronic splicing enhancers, or exonic or intronic splicing silencers. The former enhance and the latter repress splicing in nearby splice sites.
6. The Drosophila half-pint protein is _____________
a) Positive regulator
b) Negative regulator
c) Non regulator
d) Not related to fly ovarian protein
Explanation: An activator that promotes a particular alternative splicing event in a specific tissue type is the Drosophila half-pint protein. This activator regulates the alternative splicing of a set of pre-mRNA in the fly ovary.
7. Most silencer proteins are able to bind to pre-mRNA but cannot recruit the splicing machinery.
Explanation: Most silencers are recognized by members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family. These bind RNA but lack the RS domains and so cannot recruit the splicing machinery.
8. hrRNPA1 acts as the repressor for the final mRNA form of ____________
Explanation: The hrRNPA1 binds to an exonic silencer element within an exon of the HIV at pre-mRNA and represses the inclusion of that exon in the final mRNA. Bi binding to its site, the repressor blocks binding of the activator SC35 to a nearby enhancer element.
9. The pre-mRNA binding minor splicosome is also known as ___________
a) AG – CT splicosome
b) AT – GC splicosome
c) AC – AG splicosome
d) AT – AC splicosome
Explanation: The minor splicosome recognizes rarely occurring introns having consensus sequences distinct from the sequences of most pre-mRNA introns. This recently discovered form is known as the AT – AC splicosome, because the termini of the originally identified rare introns contain AU at the 5’ splice site and AC at the 3’ site in RNA or AT and TC in DNA.
10. hnRNPI binds to which segment of the mRNA?
a) 5’ splice site
b) Branch point site
c) 3’ splice site
d) AT – AC splicosome
Explanation: The hnRNPI binds to the pyrimidine tract of the intron. Thus it is also known as the polypyrimidine tract-binding protein. This is a repressor protein which when binds to the mRNA blocks the binding of the splicosome machinery.
11. Alternative splicing of the Troponin T gene produces ____________ alternative forms of mRNA.
Explanation: A region of the Troponin T gene encodes 5 exons. After splicing they recombine in such a way that only two forms of mRNA are generated. One contains exon 1, 2, 4 and 5 known as the β-tropoinin T mRNA whereas the other containing exon 1, 2, 3 and 5 known as the α-tropoinin T mRNA.
12. Which of the following mRNA is an example of having an extended exon?
a) Human slo gene
b) Mammalian muscle Troponin T mRNA
c) T-antigen mRNA of monkey virus SV40
d) Drosophila Dscam mRNA
Explanation: The pre-mRNA of the T-antigen of monkey virus SV40 contains 3 exons interrupted by 2 introns. These are spliced in 5 different alternative pathways – normal, exon skipped, exon extended, intron retained and alternative exons.
13. Alternative splicing is always used to produce multiple isoforms of proteins.
Explanation: Some genes that encode only a single functional protein show alternative splicing. In those cases, alternative splicing is used simply as a way of switching expression of the gene on and off.
14. Alternative splicing can be used to switch off a gene’s expression. How many ways are there to achieve it?
Explanation: There are 2 alternative splicing can be used to switch off a gene’s expression. Most straightforwardly, alternative splicing determines the presence of a stop codon to be included with the exons as stop codons are extensively found in the intronic regions. The second way is by regulating the use of an intron, which, when retained in the mRNA, ensures that species is not transported out of the nucleus and so is never translated.
15. Alternative splicing was discovered in the year ______________
Explanation: Alternative splicing was discovered in the studies of gene expression in the mammalian adenovirus, where mRNAs are alternatively spliced. It was discovered in the year 1977.
16. Which of the following is not a part of the minor splicosome machinery?
Explanation: U2 is not a part of the minor splicosome machinery and is only found in the major splicosome machinery. Instead U12 is found in the minor splicosome machinery and is known to recognize different sites from the U2 snRNP although carrying out the same function as U2.
Sanfoundry Global Education & Learning Series – Molecular Biology.
To practice all areas of Molecular Biology, here is complete set of 1000+ Multiple Choice Questions and Answers.