Question

draw the structure of asp-ala-his (aspartyl alanyl histidine) in the ionic form that predominates at ph 7.5. put an arrow pointing

Answer 1

The Asp-Ala-His peptide at pH 7.5 is represented as a zwitterion, with the aspartic acid side chain negatively charged, the histidine side chain positively charged if protonated, and alanine neutral. The N-terminus is positively charged, and the C-terminus is negatively charged.

Step-by-step explanation:

The student has asked to draw the structure of aspartyl alanyl histidine (Asp-Ala-His) in the ionic form that predominates at pH 7.5. At this pH, the aspartic acid (Asp) side chain would have lost its proton, giving it a negative charge, while the histidine (His) side chain can carry a positive charge due to the protonation of its imidazole ring. Alanine (Ala), however, does not carry a charge at this pH. The amino N-terminus of the peptide would be protonated and carry a positive charge, while the carboxyl C-terminus would be deprotonated and carry a negative charge, resulting in the compound overall being a zwitterion.

Amino acids at physiological pH typically exist in their zwitterionic form, with the amino group carrying a positive charge and the carboxyl group carrying a negative charge. However, side chain pKa values influence whether side chains are charged or neutral. For Asp-Ala-His, at pH 7.5, Aspartate's side chain (COOH) loses a proton to become negatively charged (COO-), and Histidine's side chain (with a pKa close to 6) can accept a proton on its imidazole ring to become positively charged. Alanine's side chain remains neutral due to its non-ionizable methyl group.

Answer 2

Asp-ala-his (aspartyl alanyl histidine) at pH 7.5 consists of aspartate with a negative charge, alanyl as neutral, and histidine which could be positively charged on the imidazole ring. The peptide bonds would connect each amino acid, with charged termini (NH3+ and COO-).

Step-by-step explanation:

The structure of asp-ala-his (aspartyl alanyl histidine) at pH 7.5 would include the amino acids in their ionized forms which predominate under physiological conditions. The aspartate (asp) side chain would bear a negative charge, the alanyl (ala) side chain remains neutral, and the histidine (his) side chain could be positively charged on the imidazole ring depending on its environment, despite being close to its pKa and potentially uncharged at pH 7.5.

Each amino acid within the tripeptide would be linked through peptide bonds, with the free amino group at the N-terminus and the free carboxyl group at the C-terminus both existing as charged species (NH3+ at the N-terminus and COO- at the C-terminus).