Calculate the overall charge of the following peptide at pH = 6.0. The N-terminus is on...

Calculate the overall charge of the following peptide at pH = 6.0. The N-terminus is on the left and C-terminus is on the right. Please use Table 5.1 in your textbook or eText for any pKa values you might need. Also, please refer to Figure 5.3 to interpret the 3-letter amino acid abbreviations. Met - Arg - Lys - Asp - Val - Gln

Solutions

Expert Solution

the pKa values of the end amino group, carboxylic acid group and side chains are given. Amide group is not considered for the analysis.

Condition.

If pH is greater than pKa of carboxylic group, COO^- will be the predominent form.

If pH is greater than pKa of amino group, -NH₂ will be the predominent form.

If pH is lesser than pKa of carboxylic group, COOH will be the predominent form.

If pH is lesser than pKa of amino group, -NH₃⁺ will be the predominent form.

According to the above rules, the existing structure of the given peptide is represented as structure 2

The structure contains three positive charges (1 from side chain of Arg; 1 from Lys side chain; 1 from terminal NH₃⁺) and two negative charges ( 1 from side chain of Asp; 1 from terminal COO^-)

adding up 3+ and 2-, we get the total charge as +1.

Answer

At pH 6, overall charge of the given peptide would be +1 (unit positive charge)

queen_honey_blossom answered 1 year ago

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