1. CHAPTER 19 Problems

2. Learning Check

3. Solution Nonpolar (NP) Polar (P)

4. 1) CH 3 2) CH 3 + | | H 3 N—CH—COOH H 2 N—CH—COO – Which structure represents: A. alanine at a pH above its p I ? B. alanine at a pH below its p I ? Learning Check

5. 1) CH 3 2) CH 3 + | | H 3 N—CH—COOH H 2 N—CH—COO – Which structure represents: A. alanine at a pH above its p I ? B. alanine at a pH below its p I ? Solution (2) (1)

6. Learning Check Draw the condensed structural formula, and give the name and abbreviation for 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

7. Solution OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N—CH—C—O – + H 3 N—CH—C─O – Ser peptide Thr bond OH CH 3 | CH 2 O H HCOH O + | ║ | | ║ NH 3 —CH—C─N—CH—C—O – + H 2 O Seryl-Threonine (Ser-Thr)

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

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

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

11. Solution What are the possible tripeptides formed 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

12. © 2013 Pearson Education, Inc. Chapter 19, Section 1 12 Learning Check Write the name and three-letter abbreviation for the following tetrapeptide. H 3 N–CH– C–N–CH– C–N–CH–C–N–CH– CO – + CH 3 O HCH 2 OH O H O CH–CH 3 CH 3 SH S CH 3

13. © 2013 Pearson Education, Inc. Chapter 19, Section 1 13 Solution Ala-Leu-Cys-Met Alanylleucylcysteylmethionine AlaLeuCys Met H 3 N–CH– C–N–CH– C–N–CH–C–N–CH– CO – + CH 3 O HCH 2 OH O H O CH–CH 3 CH 3 SH S CH 3

14. Indicate the type of protein structure as: 1) primary 2) alpha helix 3) beta-pleated sheet 4) triple helix A. polypeptide chains held side by side by H bonds B. sequence of amino acids in a polypeptide chain C. corkscrew shape with H bonds between amino acids D. three peptide chains woven like a rope Learning Check

15. Indicate the type of protein structure as: 1) primary 2) alpha helix 3) beta-pleated sheet 4) triple helix 3 A. polypeptide chains held side by side by H bonds 1 B. sequence of amino acids in a polypeptide chain 2 C. corkscrew shape with H bonds between amino acids 4 D. three peptide chains woven like a rope Solution

16. Select the type of tertiary interaction of the following. A. leucine and valine B. two cysteines C. aspartic acid and lysine D. serine and threonine 1) disulfide2) ionic 3) H bonds4) hydrophobic Learning Check

17. Select the type of tertiary interaction of the following. 4 A. leucine and valine 1 B. two cysteines 2 C. aspartic acid and lysine 3 D. serine and threonine 1) disulfide2) ionic 3) H bonds4) hydrophobic Solution

18. Identify the level of protein structure of the following. A. beta-pleated sheet B. order of amino acids in a protein C. a protein with two or more peptide chains D. the shape of a globular protein E. disulfide bonds between R groups 1) primary2) secondary 3) tertiary 4) quaternary Learning Check

19. Identify the level of protein structure of the following. 2 A. beta-pleated sheet 1 B. order of amino acids in a protein 4 C. a protein with two or more peptide chains 3 D. the shape of a globular protein 3 E. disulfide bonds between R groups 1) primary2) secondary 3) tertiary 4) quaternary Solution

20. What are the products of the complete hydrolysis of the tripeptide Ala-Ser-Val? Learning Check

21. What are the products of the complete hydrolysis of the tripeptide Ala-Ser-Val? The products are the three amino acids: alanine, serine, and valine. Solution

22. Tannic acid is used to form a scab on a burn. An egg is hard-boiled by placing it in boiling water. What is similar about these two events? Learning Check

23. Tannic acid is used to form a scab on a burn. An egg is hard-boiled by placing it in boiling water. What is similar about these two events? Acid and heat cause the denaturation of protein. They both break bonds in the secondary and tertiary structures of proteins. Solution