Chapter 19: Q66 (page 762)

Calculate the isoelectric point for each amino acid.
a. cysteine: ${pK}_{a}$ (COOH) = 2.05; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =10.25
b. methionine: ${pK}_{a}$ (COOH) = 2.28; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =9.21

Short Answer

Expert verified

a. 6.15

b. 5.75

Step by step solution

Step 1:Isoelectric point

The isoelectric point (PI) calculates the pH where charges are balanced. The balanced charges may acquire positive or negative charges in a particular medium.

Formula to calculate the PI

The formula to calculate the PI is shown as:

$PI = \frac{{pK}_{1} + {pK}_{2} + {pK}_{3 . . . . . . . . .} + {pK}_{n}}{n}$

Step 3:Explanation

a. Isoelectric point of cysteine is calculated as:

$PI = \frac{{pK}_{a} (COOH) + {pK}_{a} (α - {NH}_{3}^{+})}{2} = \frac{2.05 + 10.25}{2} = 6.15 b . Isoelectric point of methionine is calculated as PI = \frac{{pK}_{a} (COOH) + {pK}_{a} (α - {NH}_{3}^{+})}{2} = \frac{2.28 + 9.21}{2} = 5.75$

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Calculate the isoelectric point for each amino acid.
a. cysteine: ${pK}_{a}$ (COOH) = 2.05; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =10.25
b. methionine: ${pK}_{a}$ (COOH) = 2.28; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =9.21

Short Answer

Step by step solution

Step 1:Isoelectric point

Formula to calculate the PI

Step 3:Explanation

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Calculate the isoelectric point for each amino acid.a. cysteine: pKa (COOH) = 2.05; pKa(α-NH3+)=10.25b. methionine: pKa(COOH) = 2.28; pKa(α-NH3+)=9.21

Short Answer

Step by step solution

Step 1:Isoelectric point

Formula to calculate the PI

Step 3:Explanation

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Organic Chemistry

Chemical Reactions

Making Measurements

Ionic and Molecular Compounds

Inorganic Chemistry

Study anywhere. Anytime. Across all devices.

Calculate the isoelectric point for each amino acid.
a. cysteine: ${pK}_{a}$ (COOH) = 2.05; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =10.25
b. methionine: ${pK}_{a}$ (COOH) = 2.28; ${pK}_{a}$ $(α - {NH}_{3}^{+})$ =9.21