One sequence of amino acids respects for long distances in silk protein. Complete hydrolysis of one mole of a fragment with this sequence gives 2 mol alanine, 3 mol glycine, and 1 mol serine. Partial hydrolysis yields Ala-Gly-Ala, Gly-Ala-Gly, Gly-Ser-Gly, and Ser-Gly-Ala peptides. What is the amino acid repeat:a)Gly-Gly-Ser-Ala-Gly-Alab)Gly-Gly-Gly-Ala-Ala-Serc)Ser-Ala-Ala-Gly-Gly-Glyd)Gly-Ser-Gly-Ala-Gly-AlaCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

Explanation:

The given information states that one mole of a fragment with a specific sequence of amino acids gives 2 mol alanine, 3 mol glycine, and 1 mol serine upon complete hydrolysis.

Partial hydrolysis yields four peptides: Ala-Gly-Ala, Gly-Ala-Gly, Gly-Ser-Gly, and Ser-Gly-Ala.

It can be observed that Gly occurs the most frequently in the partial hydrolysis peptides, and it also occurs the most frequently in the complete hydrolysis product.

Therefore, the amino acid repeat should start with Gly.

The sequence of partial hydrolysis peptides can be used to determine the order of the amino acids in the repeat.

The partial hydrolysis peptides are Gly-Ala-Gly, Ala-Gly-Ala, Gly-Ser-Gly, and Ser-Gly-Ala.

The repeat should be a sequence that includes all of these peptides, in the order they are given.

Gly occurs twice in a row in the first partial hydrolysis peptide, so the repeat should have two consecutive Gly.

Ala occurs before and after Gly in the first and second partial hydrolysis peptides, respectively, so the repeat should have two consecutive Ala.

Ser occurs before and after Gly in the third and fourth partial hydrolysis peptides, respectively, so the repeat should have Ser in between two Gly.

Therefore, the amino acid repeat is Gly-Gly-Ala-Ala-Gly-Gly.

Option B is the correct answer.

Answer

D

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