1 / 22

Chapter Outline

Chapter Outline. Amino Acids Amino acid classes Stereoisomers Bioactive AA Titration of AA Modified AA AA reactions Peptides Proteins Protein structure Fibrous proteins Globular proteins. 5.1 Amino Acid: Definition. Generic amino acid at physiological pH: zwitterion form. a C.

gypsy
Download Presentation

Chapter Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter Outline • Amino Acids • Amino acid classes Stereoisomers • Bioactive AA Titration of AA • Modified AA AA reactions • Peptides • Proteins • Protein structure • Fibrous proteins • Globular proteins

  2. 5.1 Amino Acid: Definition Generic amino acid at physiological pH: zwitterion form aC • An alpha amino acid is a carboxylic acid with an amino group on the carbon alpha to the carboxylic acid . • The alpha carbon also has an R group side chain except for glycine which has two Hs.

  3. Definition, cont. a carbon Mirror plane • If the R group is not H, the AA can exist in two enantiomeric forms (nonsuperimposable mirror image) forms.)

  4. Amino Acids • General form: 1. an amino acid (AA); 2. two AA linked to form the peptide bond. L-form

  5. Amino Acids-2 • Only the L form of amino acids is commonly found in proteins. • Depending on the nature of the R group, AA are classified into four groups. • nonpolar • polar • acidic • basic

  6. AA with nonpolar side chains-1

  7. AA with nonpolar side chains-2

  8. AA with polar side chains-1

  9. AA with polar side chains-2

  10. AA: acidic and basic

  11. Amino Acid Titration • At physiological pH, the carboxyl group of the AA is negatively charged and the amino group is positively charged. • Amino acids without charged side chains are zwitterions and have no net charge. H3+N-CHR-COO-. • A titration curve shows how the amine and carboxyl groups react with hydrogen ion.

  12. Amino Acid Titration-2 • At low pH a nonacidic/nonbasic amino acid is protonated and has the structure below. • H3N+CHRCOOH • The charge behavior of acidic and basic AAs is more complex.

  13. Titration of Alanine C B=C pK2=9.73 B, pI=pH=6.0 A=B pK1=2.3 A 1

  14. Isoelectric point • The isoelectric point (pI) for an AA occurs when there is no net charge. • For a neutral AA, the pI is calculated using the equation pK1 + pK2/2 • Eg.: alanine: 2.34 + 9.7 / 2 = 6.0 • For acidic or basic AAs, the pI is the average of the two pKa values bracketing the isoelectric structure.

  15. Isoelectric point-2 • In general the pI is the average of the two pKa’s bracketing the isoelectric structure. Eg.: glutamic acid, pI = 3.2 pK3=9.9 pK2=4.3 pK1=2.2

  16. 5.2 Peptides • Peptide: a polymer of about 2-100 AAs linked by the peptide(amide) bond. As the amino group and the carboxyl group link, water is lost.

  17. Peptides-2 • A peptide is written with the N-terminal end to the left and the C-terminal end to the right. • H2N-Tyr-Ala-Cys-Gly-COOH • Name = Tyrosylalanylcysteinylglycine • The peptide bond is rigid and planar due to the resonance contribution shown right.

  18. Peptides-3 • The peptide bond angles force specific conformations of proteins and, on extended chains, successive R groups are on opposite sides.

  19. Physiologically Interesting Peptides b carbon Common name: carnosine found in muscle tissue

  20. Physiologically Interesting Peptides Glutathione: the reduced form reduces oxidizing agents by dimerizing to form the disulfide bond with release of 2 H.

  21. Physiologically Interesting Peptides Short form description for a peptide. Leucine enkephalin: a natural analgesic found in the brain Tyr-Gly-Gly-Phe-Leu C-terminal AA N-terminal AA

  22. Physiologically Interesting Peptides 3 8 Oxytocin Induces labor and aids in forcing milk from the mammary glands. Vassopressin has a Phe at position 3 instead of Ile and an Arg at position 8 instead of a Leu. Its role is in regulating blood pressure.

More Related