A partial peptide sequence for the wild type and three mutant alleles of a gene

Question

A partial peptide sequence for the wild type and three mutant alleles of a gene are shown below.  Each mutant was caused by a single point mutation.

Question 2 (9 points) A partial peptide sequence for the wild type and three mutant alleles of a gene are shown below. Each mutant was caused by a single point mutation. Wild type: met ile arg met asp lys trp... Mutant 1: Mutant 2: Mutant 3 met ile ser met asp lys trp... a Using the amino acid sequence of the wild type and the three mutants, deduce the exact DNA sequence of the coding strand of the wild-type allele. You will need to analyze all three mutants, which were caused by single point mutations, to decipher the exact sequence of the wild-type and mutant alleles. (Note: if after examining the wild-type and mutant alleles there still remain multiple nucleotide possibilities at a given position, you should indicate all possible nucleotides. For example if the codon is AT ,where the third base could be either Cor G, you would write AT(T/C/G) to denote the multiple possibilities at the third position.) b) Describe the nature of each mutation in mutants 1, 2 and 3. You should describe whether the mutation is a transition, transversion, or indel AND whether the mutation is a missense, nonsense, or frameshift mutation. c) Describe what consequence each of the above-mentioned DNA mutations will have on the function of the protein?

Explanation / Answer

Met

Ile

Arg

Met

Asp

Lys

Trp

Wild-type

AUG

AUC

AUU

AUA

CGU

CGA

CGG

CGC

AGA

AGG

AUG

GAU

GAC

AAA

AAG

UGG

Mutant 1

Met:

Ile:

Gln: CAA

CAG

Asn: AAU

AAC

Gly:GGA

GGU

GGG

GGC

-

-

Mutant 2

Met:

Ile:

Arg:

Met:

Gly:

Lys:

Trp:

Mutant 3

Met:

Ile:

Ser: UCU

UCA

UCG

UCC

AGC

AGU

Met:

Asp:

Lys:

Trp:

a) The exact DNA sequence of the coding strand of the wild-type allele:

ATG AT(C/T/A) AGA ATG GA(C/T) AAA TGG

b) Mutant 1: ATG AT(C/T/A) cAG AAT GGA...

insertion of c created a frameshift and the 3rd amino acid Arg changed to Gln and 4th and 5th also changed.

Mutant 2: ATG AT(C/T/A) AGA ATG GgA (C/T)AAA TGG

insertion of g changed Asp to Gly at the 5th amino acid position and introduced a frameshift while deletion of (C/T) nullified the frame shift introduced by g insertion earlier. Thus Lys and Trp are unaltered.

Mutant 3: ATG AT(C/T/A) AGA (c/t) ATG GA(C/T) AAA TGG

transversion of A to (c/t) ie., Purine to pyrimidine, altered Arg to Ser in 3rd position.

c) mutant 1 will be completely different protein from that of the wild type. It may or may not have a specific function.

Mutant2: the charged and polar aspartate is altered to aliphatic nonpolar glycine. It may have altered hydrophobicity.

Mutant 3: basic and polar arginine is altered to hydroxyl and polar amino acid serine. It will not have much change since a polar amino acid is altered to another polar amino acid.

Met

Ile

Arg

Met

Asp

Lys

Trp

Wild-type

AUG

AUC

AUU

AUA

CGU

CGA

CGG

CGC

AGA

AGG

AUG

GAU

GAC

AAA

AAG

UGG

Mutant 1

Met:

Ile:

Gln: CAA

CAG

Asn: AAU

AAC

Gly:GGA

GGU

GGG

GGC

-

-

Mutant 2

Met:

Ile:

Arg:

Met:

Gly:

Lys:

Trp:

Mutant 3

Met:

Ile:

Ser: UCU

UCA

UCG

UCC

AGC

AGU

Met:

Asp:

Lys:

Trp:

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