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Excerpt from Chapter 19: Proteins

Excerpt from Chapter 19: Proteins. University of Louisiana at Lafayette CHEM 125, Leonard All images used with permission of publisher (Cengage Learning). Zwitterion. A zwitterion has two oppositely charged ions which exist in the same molecule. a. O. H 3 N. CH. C. O. R. +. −.

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Excerpt from Chapter 19: Proteins

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

  2. Zwitterion • A zwitterion has two oppositely charged ions • which exist in the same molecule. a O H3N CH C O R + − • The zwitterion can only exist in solution • which is at the isoelectric pH. 2

  3. Zwitterion • If the pH is too low, the solution is too acidic, • the carboxylic salt end will gain H+. O O a H3N H3N CH CH C C OH O + H+ R R − + + a positive charge 3

  4. Zwitterion • If the pH is too high, the solution is too basic. • The amine salt end will lose H+. O O a H3N H2N CH CH C C O O R R + − − − H+ negative charge 4

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

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

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

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

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

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

  11. Structural Elements of Proteins III. 3o 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. • Hydrogen Bonding – R groups with an • H attached to an O, N, or F is attracted to • other O, N, or F atoms. Hydrophobic Interactions – nonpolar R groups attract other nonpolar R groups.

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

  13. Structural Elements of Proteins III. 3o Structural Elements If the following two R groups were in close proximity along a protein chain, what 3o attractions would you see? a) O HO−CH2CH2−AA AA−C−NH2 hydrogen bonding

  14. Structural Elements of Proteins III. 3o Structural Elements If the following two R groups were in close proximity along a protein chain, what 3o attractions would you see? b) CH3CH2-CH−AA AA−CH2CH3 CH3 hydrophobic interaction

  15. Structural Elements of Proteins IV. 4o 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.

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