The substituents R₁ and R₂ for nine peptides are listed in the table given below. How many of these peptides are positively charged at pH =7.0 ? array |c|c|c| Peptide & R _ 1 & R _ 2 I & H & H II & H & CH ₃ III & CH ₂ COOH & H IV & CH ₂ CON

Question

The substituents R₁ and R₂ for nine peptides are listed in the table given below. How many of these peptides are positively charged at pH =7.0 ? array |c|c|c| Peptide & R _ 1 & R _ 2 I & H & H II & H & CH ₃ III & CH ₂ COOH & H IV & CH ₂ CONH ₂ & ( CH ₂ )₄ NH ₂ V & CH ₂ CONH ₂ & CH ₂ CONH ₂ VI & ( CH ₂ )₄ NH ₂ & ( CH ₂ )₄ NH ₂ VII & CH ₂ COOH & CH ₂ CONH ₂ VIII & CH ₂ OH & ( CH ₂ )₄ NH ₂ IX & ( CH ₂ )₄ NH ₂ & CH ₃ arr

Quantrex Academy · Accepted Answer

Correct answer: 4

Peptides with isoelectric point (pI) more than 7 would exist as cation in neutral solution ( pH =7) which means the given polypeptide is of basic nature, so it must contain two or more amino groups. Hence IV, VI, VIII and IX are correct options.

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