1. Proteins and Amino Acids
Bahiya Osrah

2. Introduction The amino acids are the building blocks of Proteins
Proteins are the fundamental structural components of the body
Enzymes
Contractile proteins in the muscles to permit movement
Collagen in the bones
Plasma albumin, hemoglobin in blood
Immunoglobin to destroy infectious bacterial and viruses
Storage proteins (ferrin that bind to iron and help in its storage)
Maintain the osmotic pressure

3. Introduction More than 300 different amino acids are known in nature
Only 20 are commonly found as constituents of mammalian proteins

4. Amino acids structure At physiologic PH= 7.6 the amino acids
exists as Zwitterion
The carboxyl group dissociate to form coo –
The amino group is protonate to form NH3+

5. Zwitterion

6. Protein formation
N terminal
C terminal

7. Physical properties Colorless Crystalline
More soluble in water than in polar solvents
They have high melting points more than 200 C

8. Nutritional classification of amino acids
Non-essential amino acids
Essential amino acids:
Cannot be synthesized by the body
Must be taken from the diet
Ex: Valine, leucine, isoleucine, phenylalanine, and tryptophan
Can be made by the body

9. Classification according to amino acids side chain

10. Qualitative Tests for Amino Acids

11. 1- Ninhydrin Reaction:
A color reaction given by amino acids and peptides on heating with the chemical ninhydrin.
The technique is widely used for the detection and quantitation (measurement) of amino acids and peptides.
Ninhydrin is a powerful oxidizing agent which reacts with all amino acids between pH 4-8 to produce a purple colored-compound.

12. 1- Ninhydrin Reaction
The reaction is also given by primary amines and ammonia but without the liberation of Co2
The amino acids proline and hydroxyproline also reacts but produce a yellow color.
Alpha-amino acid + 2 ninhydrin ---> CO2 + aldehyde + final complex (purple) + 3H2O

13. 1- Ninhydrin Reaction Method:
1 ml AA + 1 ml NH---- heat in boiling WB for 5min-----Purple color

14. 2-Xanthoproteic Reaction:
This reaction is specific for aromatic amino acids
This reaction involves the nitration of benzene nucleus in alkaline medium
L-Phenylalanine
L-Tryptophan
L-Tyrosine

15. 2-Xanthoproteic Reaction:
Aromatic AAs form yellow nitro derivative on heating with conc. nitric acid, the salts of these derivatives are orange.
Nitrated tyrosine (a) and tryptophan (b)

16. 2-Xanthoproteic Reaction:
Method:
1 ml AA + 1 ml conc. HNO3----- heat the mixture in WB for 30s--cool--add drop-wise 40% NaOH to render the solution alkaline--- Yellow to orange color.

17. 3- Millon Reaction:
This reaction is used to detect the presence of phenol (hydroxybenzene) which reacts with Millon's reagent to form red complexes.
- The only phenolic AA is tyrosine.
L-Tyrosine

18. 3- Millon Reaction: Method:
1 ml AA + 5 drops of Millon reagent ----- heat the mixture in BWB for 10min--cool too room temp--add 5 drops of NaNO2---Brick red color.

19. 4- Hopkin-cole Reaction:
This reaction is used to detect the presence of indol group
The indol group of tryptophan reacts with glyoxalic acid in the presence of conc. H2SO4 to give purple color.
L-Tryptophan

20. 4- Hopkin-cole Reaction:
Method:
1 ml AA + 1 ml Hopkin-cole reagent -----mix well--Carefully pour conc. H2SO4 down the side of the tube so as to form two layers --Purple ring at the interface.

21. 5- Sulfur Test:
This reaction is specific to detect the presence of sulfur
-The sulfur of cystein and cystine is converted to inorganic sulfide with conc. NaOH. Lead acetate is added and a ppt of black lead sulfide indicates a +ve reaction.
L-Cystein

22. 5- Sulfur Test:
Method:
2 ml AA + 1 ml 40% NaOH drops of lead acetate solution----- heat the mixture in WB for 3min -----cool--observe any change ----- Black ppt.

23. 6-Sakaguchi Reaction:
This reaction is used to detect the presence of guanidine group.
-The only AA that contains guanidine group is arginine which reacts with α-naphthol and an oxidizing agent such as bromide water to give a red color
L-Arginine

24. 6-Sakaguchi Reaction: Method:
2 ml AA + 1 ml 2M NaOH + 1 ml ethanolic 0.02% α-naphthol ----- mix wellcool in ice-----add 1 ml of alkaline hypochlorite solution---- Red color