Below is a DNA template strand for part of a gene. The transcriptional start sit
ID: 163156 • Letter: B
Question
Below is a DNA template strand for part of a gene. The transcriptional start site is the first base given. Indicated in the DNA sequence are introns (parenthetical bases).
3'-TAATACACCACAC(CACCTATCTTC)TAAGATCAC(CACTCAGTTTC)CCTTCTAarrowTACTG-5'
While studying this protein you discover cell populations with different mutations described below.
a) Population one has a mutation causing only a dipeptide to be produced. Describe the change that occurred to cause production of a dipeptide.
b) Population two has an insertion of two nucleotides, CT, after position 52 (T; denoted by arrow). Illustrate and describe the effect this mutation has on protein synthesis.
Explanation / Answer
For any transriptional start site it is necessary that it has got all the necessary components right. Now we are here to start from a T, this we know that is an exon site. Now addressing the questions we have to look at the changes caused by the mutation,
a) When we see only a dipeptide is getting produced that means is that every after two codons are coded there is a termination codon that hinders the peptide chain length.
3'-AUUAUGUGGUGUGAUUCUAGUGGGAAGAUarrowAUGAC-5' - This must be the converted mRNA from the DNA template excluding the introns, so from this we can make out our own pertide sequence from the codons. So the mutation must be thus created of formed as
b) In case of second type of mutation we have the mRNA sequence as
3'-AUUAUGUGGUGUGAUUCUAGUGGGAAGAUGAAUGAC-5' This protein systnheis mechinary now having two changed bases, and thus the codon sequence also changes, now we can see that we have no stop sequence, so it seems to have a nonstop protein synthesis through mutation.
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