Amino acids, peptides and proteins

1. Kharkiv National Medical University Department of Medical and Bioorganic chemistry «Biological and Bioorganic Chemistry» Lecture № 4 Amino acids, peptides and proteins Lecturer: As. Professor, Department of Medical and Bioorganic Chemistry,, Ph.D. Levashova O.L.

2. Plan of lecture • Classification of amino acids. Stereoisomerism. • Ionic state • Quantitative reactions of amino acids. • Specific reactions of α, β and γ-amino acids. • Biologically important chemical reactions. • Peptides and proteins. • Peptides and proteins. • Primary, secondary and tertiary protein structure.

3. α-aminobutyric acid β-aminobutyric acid γ -aminobutyric acid Amino acid Nearly all the naturally occurring amino acids are α-amino acids.

4. Stereoisomerism

5. all naturally occurring amino acids belong to L-series

6. Alanine (Ala) Glycine (Gly) Valine (Val) Leucine (Leu) Isoleucine (Ile) Amino acids found in proteins Aliphatic

7. Serine (Ser) Threonine (Thr) Amino acids containing OH-group

8. Aspartic acid (Asp) Glutamic acid (Glu) Amino acids containing COOH-group

9. Asparagine (Asn) Glutamine (Gln) Amino acids containing NH2 CO-group

10. Lysine (Lys) Arginine (Arg) Amino acids containing NH2 -group

11. Cysteine (Cys) Methionine (Met) Sulfur containing Amino acids

12. Phenylalanine (Phe) Tyrosine(Tyr) Aromatic Amino acids

13. Histidine (His) Proline (Pro) Heterocyclic Amino acids Tryptophan (Trp)

14. Essential amino acids Essential amino acids – are amino acids which can not be synthesized in the human body and must be supplied to the diet. Valine Leucine Isoleucine Threonine Lysine Methionine Phenylalanine Thryptophan

15. anion cation zwitterion Ionic state

16. H2O Chemical properties 1.Amphoteric character

17. + H2O Dipeptide Specific reactionsα-amino acids a) b) Diketopiperazine

18. Unsaturated carboxylic acid Specific reactionsβ-amino acids

19. - H2O Lactam (cyclic amide) Specific reactionsγ-amino acids

20. Biologically important chemical reactions 1. Transamination. Transamination – is the main way of biosynthesis of α-amino acids from α-oxo acids in the organism. The process takes place in the presence of enzymes – transaminases and coenzyme – pyridoxal phosphate (vit B6).

21. 2. Deamination. a) reductive deamination b) oxydative deamination

22. 3. Decarboxytation. Decarboxylation takes place in the organism under the influence of enzymes called decarboxylases and pyridoxal phosphate coenzyme (vitamin B6). Lys

23. Histamine (participates in allergic reactions) His αβγ Glu γ-aminobutyric acid (neuromediator)

24. Tryptophan 5-hydroxytryptophan Serotonine 5-hydroxy-β-indolyl-acetic acid

25. + H2O Peptides and proteins

26. Classification of proteins on the basis of molecular structure Proteins Globular albumins, enzymes, hormones etc. Fibrous keratin, in skin, hair, nails and wool, collagen in tendons, fibroin in silk, myosin in muscle, etc.

27. on the basis of hydrolysis products Proteins Conjugated nucleoproteins, glycoproteins, lipoproteins, phosphoproteins, metallo-proteins (hemoglobin). Simple albumins, globulins, keratin etc.

28. Structure of proteins Primary structure Primary structure – is the sequence in which the amino acids are linked in polypeptide chain. Gly-Ala-Gly

29. Secondary structure α-Helix structure β-Pleated sheet structure Secondary structure The secondary structure - is the manner in which the polypeptide chains are arranged.

30. С О H С N С О О H H N N α-Helix structure is right-handed helix with 3.6 amino acid residues per turn. Examples: myosin (found in muscles), keratin (hair, wool, nails).

31. β-Pleated sheet structure In this structure, the long peptide chains lie side by side in a zigzag manner to form a flat sheet. Each chain is held to the two neighboring chains by hydrogen bonds. Silk fibroin has this type of structure.

32. Tertiary structure is three-dimensional stricture. This structure gives the overall shape of proteins. The tertiary structure of a protein can be obtained due to folding and superimposition of various secondary structures. The examples of the proteins having tertiary structures are globular proteins. Myoglobin

33. Quaternarystructure Quaternary structure – is the overall structure of a protein having multiple subunits. Many proteins exist as stable and ordered noncovalent aggregates of more than one polypeptide chain. The quaternary structure of hemoglobin, for example, involves four subunits. Hemoglobin

34. Hydrophobic interaction Disulphide bond Ionic bond S Hydrogen bond + S H NH3 N Forces that stabilize protein structures

35. Thank you for your attention!