2. The following DN the B-he the G at the beginning of the DNA sequence? A seque

Question

2. The following DN the B-he the G at the beginning of the DNA sequence? A sequence is a small part of the coding (nontemplate) strand from the open reading frame of moglobin gene. Given the codon chart listed below, what would be the effect of a mutation that deletes 5' - GTT TGT CTG TGG TAC CAC GTG GAC TGA-3 Second Base in Codon UCU UCA Ser CCU UAU UUcje UAA Stop UGA Stop A UAG Stop UGG TrpG CAU CUU CUA CUG AUU AUC le ACC AUG Met ur ACG GUU i CGC Pro | CAC CAA Gin cG G5 AGU Ser ce CCG A AGC TIr | AMA 1.ys l AGG AAGYS AGA GAU Asp GG ?lle | Ac GCU GUA Val GCC GUG G GUA GCG GAGGlu GGA Gly C (A) The mutation precedes the gene, so no changes would occur. (B) Lysine (lys) would replace glutamine (gln), but there would be no other changes. (C) The first amino acid would be missing, but there would be no other change to the protein. (D) The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point.

Explanation / Answer

Ans. Given, coding DNA sequence = 5’-GTTTGTCTGTGGTACCACGTGGACTGA-3’

# The sequence and polarity of mRNA is exactly the same as that of coding strand, except T in DNA is replaced by U in mRNA.

So,

            mRNA = 5’-GUUUGUCUGUGGUACCACGUGGACUGA-3’

            Reading frame = 5’-GUU UGU CUG UGG UAC CAC GUG GAC UGA-3’

            AA sequence = VCLWYHVD-

# After deletion of G at the beginning-

            mRNA = 5’-UUUGUCUGUGGUACCACGUGGACUGA-3’

            Reading frame = 5’- UUU GUC UGU GGU ACC ACG UGG ACU GA -3’

            AA sequence = FVCGTTWT

## Deletion of 1 nucleotide (G) from the beginning (or, from anywhere in the reading frame) of given DNA sequence would lead to frameshift mutation.

Frameshift mutation is the insertion or deletion of on ‘n’ residues in the reading frame of mRNA, where n is NOT divisible by 3. It thus changes the reading frame of mRNA because the reading frame is shifted by a number not equal to 3 or its multiple – which is the basic unit (triplet codon) of translation.

It may result largest extent of changes in the amino acid sequence depending on the position of mutation (closer is the mutation to 5’end of mRNA, greater would be change in amino acids sequence).

So, correct option is- D. The reading frame of the sequence would shift, ----

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