1. Amino acids, peptides and proteins 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.
Primary, secondary and tertiary protein structure.

3. Amino acid
α-aminobutyric acid β -aminobutyric acid γ -aminobutyric 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. Aliphatic Amino acids found in proteins Alanine (Ala) Glycine (Gly)
Leucine (Leu)
Valine (Val)
Isoleucine (Ile)

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

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

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

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

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

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

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

14. Essential amino acids Valine Leucine Isoleucine Threonine Lysine
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. Ionic state
zwitterion
cation
anion

16. Chemical properties
1. Amphoteric character
H2O

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

18. Specific reactions β-amino acids
Unsaturated carboxylic acid

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

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. His
Histamine (participates
in allergic reactions)
Glu
α β γ
γ-aminobutyric acid (neuromediator)

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

25. Peptides and proteins
+ H2O

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. Proteins on the basis of hydrolysis products Conjugated Simple
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 Secondary structure
The secondary structure - is the manner in which the polypeptide chains are arranged.
Secondary structure
α-Helix structure
β-Pleated sheet structure

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

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

35. Thank you for your attention!