The sequence of amino acids of the protein insulin is known. Following is a list

Question

The sequence of amino acids of the protein insulin is known. Following is a list of amino acids and the number of each in insulin Insulin Amino acid alanine arginine asparagine aspartic acid cysteine glutamic acid glutamine glycine histidine isoleucine Amino acid leucine lysine methionine phenylalanine proline serine threonine tryptophan tyrosine 20 13 7 12 14 8 13 pectinase aa 4 A) Based on this table and the structures of the amino acids (Figure 5.14 in your textbook), how many negatively charged amino acids are present in this molecule? B) Based on this table and the structures of the amino acids, how many positively charged amino acids are present in this molecule? B) Based on this table and the structures of the amino acids, how many polar (but not charged) amino acids are present in this molecule? C) What is the maximum number disulfide bonds this protein can have? D) This protein has 179 amino acids. Based on the amino acid composition, this protein is predominantly neutral negatively charged positively charged

Explanation / Answer

1. Negatively charged amino acids

Amino acids having carboxylic acid side chain and lower pK value can lose + ion and called as negatively charged amin acids.

e.g. aspartic acid and glutamic acid

as per the question, 7 aspartic acid and 12 glutamic acid = 19 negatively charged amino acids

2. Positively charged amino acids.

Amino acids having higher pK value and absent of carboxylic acid side chain can gain +ion and called as positively charged amino acids.

e.g lysine, arginine, histidine

13 lysine, 5 arginine and 5 histidine = 23 positively charged amino acids

3. Polar amino acid with no charge

Amino acids having neautral charg on side chain are polar amino acids.

e.g serine, threonine, cysteine,tyrosine,asparagines,glutamine are polar amino acids with no charge.

9 serine,13 threonine, 3 cysteine, 7 tyrosine, 7 asparagine, 6 glutamine = 45 polar amino acids

4. It has maximum 3 disulfide bonds. One disulfide bong in A chain and two disulfide bond between A and B chain.

5. Most number of amino acid in insulin are polar with no charge hence it is predominantly neutral

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