The total number of negative charge in the tetrapeptide, Gly–Glu–Asp–Tyr, at pH 12.5 will be (Integer answer)

Question

The total number of negative charge in the tetrapeptide, Gly–Glu–Asp–Tyr, at pH 12.5 will be  (Integer answer)

Canvas Classes · Accepted Answer

Ionizable groups in Gly–Glu–Asp–Tyr and their pKa values:

| Group | pKa | Charge at pH 12.5 |
|---|---|---|
| N-terminus (–NH₃⁺) | ~9.0–9.5 | pH  pKa → –NH₂ (neutral, 0) |
| C-terminus (–COOH) | ~2.0–3.5 | pH  pKa → –COO⁻ (−1) |
| Glu side chain (–CH₂CH₂COOH) | ~4.1 | pH  pKa → –COO⁻ (−1) |
| Asp side chain (–CH₂COOH) | ~3.9 | pH  pKa → –COO⁻ (−1) |
| Tyr side chain (–C₆H₄OH) | ~10.1 | pH  pKa → –C₆H₄O⁻ (−1) |

At pH 12.5:

All groups with pKa < 12.5 are in their deprotonated form:
- N-terminus

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