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Biology
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9 Jan 2018

1. What are the advantages, and disadvantages of splicing?

2. What type of error does incorrect splicing cause? What do you think is the origin of these errors?

3. Would you expect introns or exons to accumulate more mutations through evolutionary time? Explain your reasoning.

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Casey Durgan
Casey DurganLv2
11 Jan 2018
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Related questions

QUESTION 1

Which of the following statements regarding splicing is FALSE?

A) The length of introns determines the efficiency of splicing.

B) Many human neurological disorders are caused by splicing errors and/or mutations in splicing factors.

C) Splicing requires the action of a variety of snRNAs that direct the transesterification reactions.

D) Splicing is dictated by sequence features in pre-mRNA transcripts

QUESTION 2

Which of the following mRNA processing factors does NOT associate with the CTD of RNA polymerase II?

A) splicing factors

B) polyadenylation factors

C) miRNAs/siRNAs

D) capping proteins

QUESTION 3

Which of the following statements about mRNA stability is FALSE?

A) Deadenylation-independent mRNA decay is exclusively in the 5' to 3' direction.

B) The most common pathway of mRNA decay is deadenylation-dependent.

C) Yeast mRNA decay occurs primarily in the 5' to 3' direction, while 3' to 5' decay is more common in mammalian cells.

D) Decapping enzymes are required for all pathways of mRNA decay.

QUESTION 4

You obtain the sequence of a gene containing 10 exons, 9 introns, and a 3′ UTR containing a polyadenylation consensus sequence. The fifth exon also contains a polyadenylation site. To test whether both polyadenylation sites are used, you isolate mRNA and find a longer transcript from muscle tissue and a shorter transcript from all other tissues. Which of the following is the most likely mechanism underlying these alternative transcripts?

A) The fifth exon is spliced out of the mature mRNA transcript in muscle cells.

B) Muscle cells have less effective polyadenylation than other tissues.

C) An alternative CPSF protein is expressed in muscle cells with lower affinity for the polyadenylation sequence in exon 5.

D) The mRNA in muscle cells is edited to eliminate the polyadenylation sequence in exon 5.

Q.1

A gene has two introns and three exons. The length of exons 1, 2 and 3 is 600, 1200 and 300 bp, respectively, which are separated by 400 bp intron-1 and 800 bp intron-2. Suppose, a mixture of the dsDNA completely covering this gene and the processed mRNA it codes for is heated at 95C for 10 minutes, gradually cooled to room temperature and then viewed under electron microscope (EM). Draw the diagram of the DNA-RNA hybrid that you expect to see under the EM and answer the following questions. You should use different color for DNA and RNA strands , and label the regions that represent dsDNA, ssDNA and RNA-DNA hybrid. The diagram must take into account the length of introns and exons.

Q.2

What is the function of SR and silencer proteins that activates and represses splicing, respectively? Name the domains that are found in these proteins and explain their function. Explain how the splicing silencer proteins inhibit the function of the SR proteins.

Question 2. Splicing is complicated. There isconstitutive splicing, and then there is regulated alternativesplicing, and these molecular events can occur in the same ordifferent tissues.

a. What is constitutive splicing?

b. What is alternative splicing?

c. Draw a gene with three exons and twointrons. In this example assume exons 1,2,3 are expressed in onetissue and exons 1,3 are expressed in another. Draw the alternativesplicing, and the resulting RNA from this gene.

d. Draw a model illustrating how sterichindrance can promote alternative splicing with in a gene.

e. An individual is heterozygous, one copy ofthe gene has a mutation in exon 1 and the other copy of the gen ehas a mutation exon 3. Draw their genes, with mutations. What RNAmolecules can be expressed from these alleles? Will thisheterozygote have a mutant or a wild - type phenotype? Explain.Assume the 1/3 variant and the 1/2/3 variant are required indifferent tissues

Question 3 . You haveidentified a 4 exon gene expressed in the nervous system of adiploid animal. Different splice variants are expressed in thenervous tissue at the same time. T he organism under study has agene, unc - 250 , that controls movement and has three differentrecessive mutant alleles: allele s a 1 , a2 , and a3 . All threemutations are nonsens e stop mutations. When a diploid organism ishomozygous for allele a 1 animals die. When homozygous for eitherallele a2 , or allele a3 , animals are very uncoordinated in theirmovement (unc). Alleles a2 and a3 fail to complement allele a1 ,that is to say a1 / a2 and a 1 / a3 heteroallelic animals are veryuncoordinated in their movement (unc). However, a2 / a3 animals arewild type, ie they complement. Using alternative splicingconstruct a logical model for these observations and show whereeach of the mutations would be located in the gene.

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