At physiological pH, the carboxy-terminal of a peptide is -

Ans. is 'b' i.e., Negatively charged Net charge of Aminoacids at neutral pH.At Physiological pH, all amino acids have both a negatively charged group, carboxyl ion (COO- ) and a positively charged group Ammonium ion, (-NH3+). The amino acids are therefore dipolar ion (Zwitter ions). Zwitter ions - Molecules that contain an equal number of ionizable groups of opposite charge and therefore bear no net charge are termed Ziwetter ions.Also know isoelectric pointAt neutral pH amino acids exists predominantly as the dipolar form II in which the amino and carboxyl groups are ionized, but the net charge is zero.Thus isoelectric point is the pH at which an amino acid is electrically neutral - that, is, where the sum of the positive charges equals the sum of the negative charges.AmpholytesSubstances such as amino acids that can act either as an acid or base are defined as amphoteric and are referred to as ampholytes (amphoteric electrolytes).