Question

odon number Normal 506 507 508 509 510 511 Mutant ene (coding strand) ATC ATCTT GGT GTTT gene (coding strand) ATc ATX XXT GGT TCC GTT TCC What effect will this mutation have on the amino acid sequence of the protein encoded by the CFTR A Deletion of a phenylalanine residue with no change in the C-terminus sequence. B. Deletion of a leucine residue with no change in the sequence. C. Deletion of a phenylalanine residue with a change in the C-terminus sequence. D. Deletion of a leucine residue with a change in the C-terminus sequence. 25) Phenylketonuria (PKU) is an autosomal recessive genetic disorder that results from an mutation in the gene coding for the As a result of this mutation, those with PKU are unable to phenylalanine hydroxylase enzyme. phenylalanine. Excess metabolize phenylalanine and convert it into tyrosine. resulting in a build-up of phenylalanine is then metabolized to form phenylpyruvate via the action of the enzyme dangerous transaminase. Without enzymes to remove phenylalanine, this amino acid can build up to levels, especially when food is consumed that is high in protein such as meat, milk, nuts, and Left untreated, PKU can lead to serious p brain damage, problems, seizures. Treatments medical with a formula containing amino acids and other essential nutrients. include a low-protein diet supplemented There have been over 300 identified mutants that result in PKU, most of which are in the catalytic Phenylalanine hydroxylase is the rate-limiting enzyme of the phenylalanine metabolic pathway. hydroxylase catalyzes the aromatic ring of phenylalanine, converting it to tyrosine. This enzyme requires two- form (BH4 subscript. 4, end subscript) and iron to function (Figure 1). Another of PKU can exist when there is a deficiency in the cofactor tetrahydrobiopterin. Figure 1: Phenyalanine is converted to tyrosine by phenylalanine hydroxylase. How would you expect the mutation associated with PKU to affect the catalytic efficiency of Please choose from one of the following options. A Keat will decrease, and Km will increase, leading to a decreased catalytic efficiency. B. Neither Keat nor Km will change, leading to an unchanged catalytic efficiency. C. Keat and Km will decrease, leading to an indeterminate effect on the enzyme's catalytic efficiency D. Koat will increase and Km will decrease, leading to an increased catalytic efficiency.

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Answer 1

Answer 1: Cystic fibrosis occurs due to deletion of amino acid sequence for phenylalanine (TTT, TTC) at position 508 of the peptide. Deletion at sequence position at 507 has no effect on it. Thus, option C is correct.

Answer 2: The enzyme kinetics follows a positive and negetive feedback loop but the overall biological activity remains unaltered in terms of Km and Kcat until any inhibitor or competetive molecule does not arrive. So, even under the situation mentioned in the question, there is no competitive inhibitor or other candidate to compete for substrate specificity. So in this situation, simply the Kcat and Km will remain unchanged and enzyme activity might be stopped by positive feedback loop. So, option B is correct.