1. 1 16.4 Formation of Peptides Chapter 16 Amino Acids, Proteins, and Enzymes Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. 2 The Peptide Bond A peptide bond is an amide bond. forms between the carboxyl group of one amino acid and the amino group of the next amino acid. O CH 3 O + || + | || H 3 N—CH 2 —C—O – + H 3 N—CH—C—O – O H CH 3 O + || | | || H 3 N—CH 2 —C—N—CH—C—O – peptide bond

3. 3 Formation of a Dipeptide

4. 4 Learning Check Write the dipeptide Ser-Thr. OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N─CH─C─O – + H 3 N─CH─C─O – Ser Thr

5. 5 Solution Write the dipeptide Ser-Thr. OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N─CH─C─O – + H 3 N─CH─C─O – Ser Thr OH CH 3 | | CH 2 O H HCOH O + | ║ | | ║ NH 3 ─CH─C─N ─CH─C─O – + H 2 O Ser-Thr

6. 6 Naming Dipeptides A dipeptide is named from the free amine (NH 3 + ) using a -yl ending for the name. names the last amino acid with the free carboxyl group (COO - ) by its amino acid name.

7. 7 Write the three-letter abbreviations and names of the tripeptides that could form from two glycine and one alanine. Learning Check

8. 8 Write the names and three-letter abbreviations of the tripeptides that could form from two glycine and one alanine. Glycylglycylalanine Gly-Gly-Ala Glycylalanylglycine Gly-Ala-Gly Alanylglycylglycine Ala-Gly-Gly Solution

9. 9 Learning Check What are the possible tripeptides formed from one each of leucine, glycine, and alanine?

10. 10 Solution Tripeptides possible from one each of leucine, glycine, and alanine: Leu-Gly-Ala Leu-Ala-Gly Ala-Leu-Gly Ala-Gly-Leu Gly-Ala-Leu Gly-Leu-Ala

11. 11 Learning Check Write the three-letter abbreviation and name for the following tetrapeptide. CH 3 │ CH 3 S │ │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–CO –

12. 12 Solution Ala-Leu-Cys-MetAlanylleucylcysteinylmethionine CH 3 │ CH 3 S │ │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–CO – Ala LeuCys Met