C) Mutations : A mutation is defined as a changein the base sequence of DNA. Thi
ID: 3108 • Letter: C
Question
C) Mutations: A mutation is defined as a changein the base sequence of DNA. This may occur as a“mistake” in DNA replication, for example.
Suppose that during DNA replication, two mutant DNA sequencesare produced as shown below.
For the 2 mutated DNA sequences, you will investigate how thesechanges might affect the sequence of amino acids in a protein.
Question: For each of the two, you will need to firsttranscribe the mRNA, and then use the genetic code table todetermine the amino acid sequence.
Turn these in, and state whether the protein sequencechanges for each.
Question: Then, explain why a change in amino acidsequence might affect protein function. Turn in youranswer.
Here is the original sequence, followed by two mutatedsequences, 1 and 2:
Original sequence 3'- TACCCTTTAGTAGCCACT-5’
Mutated sequence 1) 3’-TACGCTTTAGTAGCCATT-5'
Mutated sequence 2) 3’-TAACCTTTACTAGGCACT-5’
Explanation / Answer
For a protein to besynthesized the DNA is trancribed to m-RNA and from this m-RNAthe proteins are synthesizedby the mechanism oftranslation. In the mechanism oftranslation, protein synthesis is initiated on m-RNA where the basesequence is as AUG orrarely it is GUG. These two codons code forMethionine aminoacidat the start site(though internally GUG codes for Valine). So for a protein to besynthesized we need to have this codon. For the protein to besynthesized, the m-RNA is read in 5' to 3' direction and 3 basesare taken as a unit known as codon. Originalsequence 3'- T A C C C T T T AG T A G C C A C T -5’ Sequence ofm-RNA 5'- A U G G G A AAU C A U C G G U G A-3' Protein sequence Met---Gly----Asn---His----Arg----Stop From this originalsequence of DNA a protein of 5 amino acids is coded . The last codon is a stopcodon so it does not code for any aminoacid. Mutated sequence1) 3’-T A C G C T T T A GT A G C C A T T -5' Sequence ofm-RNA 5'-A U G C GA A A U C A U C G G UA A-3' Proteinsequence Met---Arg----Asn---His----Arg----Stop From this 1 mutatedsequence the 4th base C is replaced by G so in m-RNA we haveG instead ofC and thecodon codes for Arginine instead of Glycine. Mutated sequence2) 3’-T A A C CT T T A C T A G G C A C T-5’ Sequence ofm-RNA 5'- A U U G G A A A U G A U C C G U G A-3' This m-RNA sequence doesnot code for any protein, because there is no inititating codon inthe sequnece. As there is a mutation atthe 3rd base,where there is A instead of C in the m-RNA instead ofG ,U is placed. Due to this,instead of AUGthe codon is as AUU which codes of Isoleucine which is not a startcodon. protein synthesis is not initiatedas there is lack of start codon i.e., AUG. For each sequence there isa change in the protein. In the originalsequence,the protein has two non polar aminoacids, apolar amino acid andtwo basicaminoacids. This protein will exhibitpositive charge and will have its own set of properties whilein the mutated 1 sequence the second amino acid isArginine which ispositive aminoacid that differs from the original sequence whichhas a non polar aminoacid Glycine. Due to this the positivityof the protein increases and the protein differs from the originalone. The 2nd mutatedsequence, as it lacks the initiating codon the sequence of m-RNA isnot translated. So no protein issynthesized from this sequence. Hope you are satisfiedwith the answer. Sequence ofm-RNA 5'- A U U G G A A A U G A U C C G U G A-3' This m-RNA sequence doesnot code for any protein, because there is no inititating codon inthe sequnece. As there is a mutation atthe 3rd base,where there is A instead of C in the m-RNA instead ofG ,U is placed. Due to this,instead of AUGthe codon is as AUU which codes of Isoleucine which is not a startcodon. protein synthesis is not initiatedas there is lack of start codon i.e., AUG. For each sequence there isa change in the protein. In the originalsequence,the protein has two non polar aminoacids, apolar amino acid andtwo basicaminoacids. This protein will exhibitpositive charge and will have its own set of properties whilein the mutated 1 sequence the second amino acid isArginine which ispositive aminoacid that differs from the original sequence whichhas a non polar aminoacid Glycine. Due to this the positivityof the protein increases and the protein differs from the originalone. The 2nd mutatedsequence, as it lacks the initiating codon the sequence of m-RNA isnot translated. So no protein issynthesized from this sequence. Hope you are satisfiedwith the answer.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.