Question

Which of the pH conditions shown below would give this heptapeptide an overall charge of +2? COOH CH2 CH NH NH. CH5 HN CH NH,— сH,CH,CH,CH NH NH2 NH C но CH CH2 CH C СООН (a) The cyclic structure means that the system will always be isoelectronic (b) рH %3 3 (c) Neutral pH (d) pH 10 (e) The system will always be charged as it is a zwitterion = 40

Answer 1

In any peptide two side is present, one is N terminal i.e. free NH2 group is present and another is C terminal where free COOH group is present. When more than one amino acid is join then it's called peptide . The most stable form of amino acid is zwitter ionic form where it's in neutral form. With variation of pH they present in different form . Similarly, here in heptapeptide the dicationic form is only possible when the two free NH2 group is in protonated condition . So, it's only possible at low pH here is given pH 3 . As, at high pH COOH becomes deprotonated and anionic form is observed. Hence, the answer.