Q.1 A gene has two introns and three exons. The length of exons 1, 2 and 3 is 60
ID: 252552 • Letter: Q
Question
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.
Explanation / Answer
Q2. Splicing is the process by which Exxon’s are added or emitted from messenger RNA to form different proteins. Splicing can be done with the help of various regulators (activators and repressors).
SR proteins and hnRNPs are the important factors which acts as activators in splicing mechanism. These are splicing enhancers where activating proteins will bind. Enhancer proteins will be find on either introns or exons called intrinsic splicing enhancers or exonic splicing enhancers, respectively.
Silencers are repressive sites, where splicing repressor proteins will bind, which is found in mRNA. By binding, it will block the proteins to bind on the splicing sites. Splicing silencers will present on either introns or exons known as intrinsic splicing silencers or exonic splicing silencers, respectively.
SR protein has long residues of serine and arginine amino acids (S and R) and RNA recognition motif. Silencer has exon and intron domains.
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