21. Determine the mRNAs and proteins that will be produced from the following DN

Question

21. Determine the mRNAs and proteins that will be produced from the following DNA coding sequences: a. Wild-type DNA sequence: CCTCA DNA Template strand mRNA (1 point) Identify the Amino Acids: (1.Spoints) This is your protein product b. Repeat the process again, but this time with a mutation in the DNA! EIAETCI TGI AT GI TETA ETTI AET ] Template strand ? mRNA (1 point) Identify the Amino Acids: This is your protein product (1.5points) c. Did you get the same protein? (1 point). Second base Phe UCU UCC UGU Ul UUC UGC UUA UCA UAA Stop UGA Stop A Leu d. What type of DNA mutation occurred? (1 point) UU G UCG UAG Stop UGG Trp G CUU His GU c CUC Pro CAC GIn e. What might be a phenotypic result of that DNA mutation? (1 point) AGU AGC Ser AUA AUG Met ACG AAG Lys AGG A GGU GGC GGA Asp GUC al GCC AlGAC GUA ?GCA ?GAA GUG GCG GAG Glu Page 3 of 4

Explanation / Answer

(a) The mRNA sequence is complementary to the template strand with the T (Thymine) base in the DNA sequence is substituted by Uracil (U) in the mRNA sequence.

Thus, in the given question:

DNA seq :           ATGCCTCAGTCATGA

Template strand : TACGGAGTCAGTACT

Upon transcription, the mRNA sequence obtained : AUGCCUCAGUCAUGA

Following translation of the above mRNA, the amino acid sequence obtained is : Met-Pro-Gln-Ser

UGA : Stop codon ; thus leads to truncation of the polypeptide.

(b) The mutation at a single nucleotide in template strand is : TACCGGAGTCAGTACT

Since the mRNA sequence is complementary to the template strand, the new mRNA sequence obtained after transcription is

mRNA seq : AUGGCCUCAGUCAUGA

Protein seq : Met-Ala-Ser-Val-Met-

There occurs a change in the amino acid at the second position which replaces Pro to Ala due to change in the codon.

(c) Due to single point mutation in the template strand, the codon changes leading to replacement of Pro to Ala upon translation of the mRNA synthesized. Thus, altered protein product is obtained.

(d) Such mutation where the replacement of a single nucleotide leads to change in the amino acid within the polypeptide chain is termed as Missense mutation.

(e) Replacement of a single nucleotide with incorrect amino acid may produce a malfunctioning protein. The best example is the hemoglobin in sickle cell anemia which is due to mutation in the sixth codon of hemoglobin GAG to GTG.

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