1. Excerpt from Chapter 19: Proteins University of Louisiana at Lafayette CHEM 125, Leonard All images used with permission of publisher (Cengage Learning)

2. Zwitterion 2 H3NH3NCHCO O R + −  A zwitterion has two oppositely charged ions which exist in the same molecule. The zwitterion can only exist in solution which is at the isoelectric pH.

3. Zwitterion 3 H3NH3NCHCO O R + −  If the pH is too low, the solution is too acidic, the carboxylic salt end will gain H +. + H + H3NH3NCHCOH O R +  positive charge

4. Zwitterion 4 H3NH3NCHCO O R + −  If the pH is too high, the solution is too basic. The amine salt end will lose H +. − H + negative charge H2NH2NCHCO O R −

5. Structural Elements of Proteins I. 1 o Structural Elements The order and identity of each amino acid in the protein is it’s 1 o structural element. Diseases like sickle-cell anemia is caused by a minor sequencing error in the hemoglobin protein.

6. Structural Elements of Proteins II. 2 o Structural Elements Alpha (  ) helix – a coil held together by hydrogen bonds. Small-scale folding patterns along the protein chain are the 2 o structural elements:

7. Structural Elements of Proteins Alpha (  ) helix – a coil held together by hydrogen bonds.

8. Structural Elements of Proteins II. 2 o Structural Elements Small-scale folding patterns along the protein chain are the 2 o structural elements: Alpha (  ) helix – a coil held together by hydrogen bonds. Beta (  )-pleated sheet – a folded sheet-like shape held together by hydrogen bonds.

9. Structural Elements of Proteins Beta (  )-pleated sheet – a folded sheet-like shape held together by hydrogen bonds.

10. Structural Elements of Proteins II. 2 o Structural Elements

11. Structural Elements of Proteins III. 3 o Structural Elements Large-scale folding patterns which show how 1 protein chain folds over itself: A. Disulfide Linkage – 2 cysteine amino acids can link their thiol R groups. B. Salt Bridge – attractions between the R groups of the acidic and basic amino acids. C. Hydrogen Bonding – R groups with an H attached to an O, N, or F is attracted to other O, N, or F atoms. D. Hydrophobic Interactions – nonpolar R groups attract other nonpolar R groups.

12. Structural Elements of Proteins III. 3 o Structural Elements

13. Structural Elements of Proteins III. 3 o Structural Elements If the following two R groups were in close proximity along a protein chain, what 3 o attractions would you see? AA − C − NH 2 O HO − CH 2 CH 2 − AA a) hydrogen bonding

14. Structural Elements of Proteins III. 3 o Structural Elements If the following two R groups were in close proximity along a protein chain, what 3 o attractions would you see? b) hydrophobic interaction AA − CH 2 CH 3 CH 3 CH 2 -CH − AA CH 3

15. Structural Elements of Proteins IV. 4 o Structural Elements Large-scale folding patterns which show how 2 or more protein chains fold over each other. Hemoglobin: made up of 4 protein chains.