A deletion of a single base (nucleotide) in a structural gene results in a frame
ID: 176559 • Letter: A
Question
A deletion of a single base (nucleotide) in a structural gene results in a frameshift mutation. A deletion of two bases also results in a frameshift. A deletion of three bases returns to the original frame, but with one amino acid missing. Suppose on the imaginary planet Gowan, DNA codons were four bases instead of three. E.g., AGCG might correspond to a particular amino acid. On this planet, how many reading frames would DNA have? Explain. Fig 14.13 shows the beta-globin gene, and how the various forms of globin (epsilon, G-gamma, A-gamma, delta, and beta) have evolved through duplication and divergence. The advantage of this duplication and divergence is that it allows different forms of a protein to have different functions that benefit under different conditions, E.g., fetal hemoglobin (made before birth) differs from "adult" hemoglobin (made after birth.) What characteristic might you expect for fetal hemoglobin that distinguishes it from adult hemoglobin?Explanation / Answer
Answer 12) As we know that an amino acid is coded by a triplet codon which contains a definite pattern of three nucleotides arranged in a pair. so, if we start coding from the very first nucleotide of this codon then this is called as a first reading frame. and if we start coding from the second nucleotide of this codon then this is called as a second reading frame and lastly, if we start coding from the third nucleotide of this codon then this is called as a third reading frame. coding from the next fourth nucleotide gives the similar amino acid sequence as the first one. so here we have three reading frames in the 5'---->3' direction of the DNA. while in the proposed case, when four nucleotides codes for one amino acid, then there are four possible reading frames; as first reading frame from the first nucleotide in the given quadruplet codon, second reading frame from the second nucleotide, this reading frame from the third reading frame and fourth reading frame from the fourth nucleotide in this quadruplet codon in the 5'---->3' direction of the coding sequence.
Answer 13) As we know that a fetus has all the oxygen supply from the maternal blood and no direct gas exchange through the air. while an adult can have access to the oxygen via respiration through lungs by himself. this is the possible cause why a fetus hemoglobin must have a higher affinity to oxygen as compared with the adult hemoglobin. in short, we can describe that a fetus hemoglobin has a higher binding affinity to oxygen as compared to the adult hemoglobin because of certain amino acid alteration in its binding pocket which affects the binding affinity of the hemoglobin.
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