The isoelectric point (pI) of the amino acid is 5.65. This value is calculated by averaging the given pKa values of the carboxylic acid group (2.17) and the amino group (9.13), as the side chain is non-ionizable.

Isoelectric Point Concept

Amino acids exist as zwitterions with both positive (NH₃⁺) and negative (COO⁻) charges. The pI is the pH where net charge is zero, occurring between the two pKa values for neutral amino acids. At pH < pI, the amino acid is positively charged; at pH > pI, it is negatively charged.

Calculation Method

For amino acids with non-ionizable side chains (like glycine or alanine), use the formula:

pI = (pKacarboxyl + pKaamino) / 2

Substitute values:

pI = (2.17 + 9.13) / 2 = 11.30 / 2 = 5.65

Why This Formula Applies

Non-ionizable side chains contribute no charge, so only the α-carboxylic acid (pKa₁ ≈ 2) and α-amino group (pKa₂ ≈ 9-10) matter. The zwitterion form predominates midway between these pKa values. Acidic (e.g., Asp) or basic (e.g., Lys) side chains require averaging different pKa pairs, but that’s irrelevant here.

Introduction: Mastering Isoelectric Point Amino Acid pKa 2.17 9.13 for CSIR NET

In CSIR NET Life Sciences, understanding isoelectric point amino acid pKa 2.17 9.13 is crucial for questions on protein chemistry and electrophoresis. For amino acids with non-ionizable side chain, the isoelectric point (pI) calculation uses a simple average of carboxylic (pKa=2.17) and amino (pKa=9.13) groups, yielding pI=5.65 (rounded to two decimals). This guide breaks it down for exam success.

Step-by-Step Isoelectric Point Calculation

  • Identify pKa values: Carboxylic group (pKa₁=2.17), amino group (pKa₂=9.13). No side chain pKa needed.
  • Apply formula: pI = (2.17 + 9.13) / 2 = 5.65.
  • Verify: Matches neutral amino acids like glycine (pI≈6).

Common Exam Traps (No Options Here):

  • Don’t average with side chain pKa (irrelevant for non-ionizable).
  • Round correctly to 5.65, not 5.6 or 5.7.
  • Ignore acidic/basic rules; this is neutral.

Applications in Biochemistry

pI determines solubility minimum and migration in gel electrophoresis. For CSIR NET, know pI shifts separation in IEF. Practice with alanine (pKa 2.34, 9.69; pI=5.97).

CSIR NET Tips

Focus on zwitterion charge states vs. pH. Solve similar problems: pKa 2.3 + 9.7 = pI 6.0. Use for quick scoring in molecular biology section.