Dolbier HW Solutions 663

Dolbier HW Solutions 663 - here in its cationic form. It...

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27.10 ( b ) Alanine is the N-terminal amino acid in Ala-Phe. Its carboxyl group is joined to the nitrogen of phenylalanine by a peptide bond. ( c ) The positions of the amino acids are reversed in Phe-Ala. Phenylalanine is the N terminus and alanine is the C terminus. ( d ) The carboxyl group of glycine is joined by a peptide bond to the amino group of glutamic acid. The dipeptide is written in its anionic form because the carboxyl group of the side chain is ionized at pH 7. Alternatively, it could have been written as a neutral zwitterion with a CH 2 CH 2 CO 2 H side chain. ( e ) The peptide bond in Lys-Gly is between the carboxyl group of lysine and the amino group of glycine. The amino group of the lysine side chain is protonated at pH 7, and so the dipeptide is written
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Unformatted text preview: here in its cationic form. It could have also been written as a neutral zwitterion with the side chain H 2 NCH 2 CH 2 CH 2 CH 2 . ( f ) Both amino acids are alanine in D-Ala-D-Ala. The fact that they have the D con f guration has no effect on the constitution of the dipeptide. NHCHCO 2 2 d-A-d-A CH 3 H 3 NCHC CH 3 O 1 Alanine Alanine H 3 NCHC KG H 3 NCH 2 CH 2 CH 2 CH 2 O 1 1 Lysine NHCH 2 CO 2 2 Glycine H 3 NCH 2 C NHCHCO 2 2 GE CH 2 CH 2 CO 2 2 O 1 Glycine Glutamic acid FA H 3 NCHC C 6 H 5 CH 2 O 1 Phenylalanine NHCHCO 2 2 CH 3 Alanine AF H 3 NCHC CH 3 O 1 Alanine NHCHCO 2 2 CH 2 C 6 H 5 Phenylalanine AMINO ACIDS, PEPTIDES, AND PROTEINS. NUCLEIC ACIDS 757...
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