Amino Acid Introduction

1. AMINOACIDS
Mrs. Poonam Sunil Aher (M Pharmacy, PhD)
Assistant Professor, HOD Pharmaceutical Chemistry
Department
Sanjivani College of Pharmaceutical Education and
Research (Autonomous),
Kopargaon, Ahmednagar-423603 (M.S.), INDIA
Mobile: +91-9689942854

2. Amino Acid
Amino acids are a group of organic compounds containing
two functional groups amino and carboxyl.
The amino group (-NH2) is basic while the carboxyl group
(-COOH) is acidic in nature.

3. Classification of Amino Acids
A. Classification based on structure:
Each amino acid is assigned a 3 letter or 1 letter
symbol.
These symbols are commonly used to represent the
amino acids in protein structure

4. Amino Acids found in proteins are also can be
divided into seven distinct groups
-AA with aliphatic sidechains
-Hydroxyl group containingAA
-Sulfur containingAA
-Acidic AA and theiramides
-BasicAA
-AromaticAA
-Imino acids

12. Diamino amino acids

13. monoamino-monocarboxylic amino acids

14. monoamino-dicarboxylic amino acids

15. diamino monocarboxylic amino acids

16. B.Classification of amino acids based on polarity
There are four groups of AA depending topolarity
1.Non-polar AA (also referred as hydrophobic [water hating]) no
charge on ‘R’group
Alanine, Leucine, Isoleucine, Valine, Methionine, Phenylalanine,
Tryptophan, Proline
2.PolarAAwith no charge on ‘R’group
Glycine, Serine, Threonine, Cysteine, Glutamine, Asparagine.Tyrosine
– they however possess groups such as hydroxyl, sulfhydryl, amide
– and participate in hydrogen bonding of protein structure.
3.PolarAAwith positive ‘R’group
Lysine, Arginine, Histidine
4.PolarAAwith negative ‘R’group
Aspartic acid, GlutamicAcid

17. 20
Amino
Acids

18. Amino
Acids
non-polar,
aliphatic

19. Aromatic
Amino
Acids

20. Positively
charged
Amino
Acids

21. Negatively
charged
Amino
Acids

22. Polar,
ancharged
Amino
Acids

23. Amino
Acids
variant of
classification

24. C.Nutritional classification of amino acids
The 20AA are required for the synthesis of variety proteins,
besides other biologicalfunctions.
However, all these 20 AA need not be taken in thediet.
Based on the nutritional requirements, amino acids are grouped
into three classes:
1.Essential Amino Acid
2. Semi essential Amino Acid
3.Non-essential Amino Acid

25. Essential and non-essential amino acids
1.Essential Amino acid (or indispensable)
• The Amino acid which are cannot be synthesized by the body, and
therefore, need to be supplied through the diet are called essential
Amino Acid.
• They are required for proper growth and maintanance of the
individual.
• Arginine,Valine, Histidine Isoleucine Leucine Methionine
Phenylalanine Threonine Tryptophan
2.Semi essential Amino acid:
• Arginine and Histidine can be synthesized by adults and not by
growing children they are considered as semi-essential Amino
Acid.
• Thus 8 AA absolutely essentialwhile 2 are semi-essential.
3.Non-essential (or dispensable)Amino Acid:
Glycine, Alanine, Serine, Cysteine, Aspartate, Asparagine, Glutamate,
Glutamine,Tyrosine, Proline.

26. D.Classification based on their metabolic fate
Carbone skeleton of AA can serve as a precursor for the
synthesis of glucose (glycogenic) or fat (ketogenic) or
both.
1.Glycogenic Amino Acid(can serve as precursors for the
formation of glucoseor glycogen)
Alanine, Aspartate, Glycin, Methionine etc
2.Ketogenic Amino Acid(fat can besynthesized)
Leucine, Lysine
3.Glycogenic and ketogenicAmino Acid
Isoleucine, Phenylalanine, Tryptophan, Tyrosine –
precursors for synthesis of glucose as well as fat.

27. I. Physical properties of amino acid
1.Solubility
–most of amino acids are usually soluble in water and insoluble in
organic solvents
2.Melting point
– amino acids generally melt at higher temperature, often above 200ºC
3.Taste: Amino acids may be
-sweet (Gly, Ala,Val),
-tasteless (Leu),
-bitter (Arg, Ile)
Monosodium glutamate (MSG, ajinomoto) is used as a flavouring
agent in food industry, and Chinese food to increase taste and flavour.
In some individuals intolerant to Monosodium glutamate
(MSG),Chinese syndrome (brief and reversible flulike symptoms) is
observed.

28. I.Physical properties of amino acids
4.Optical properties – all amino acids (except Glycine)
possess optical isomers due to the presence of asymmetric
carbon atom

29. I.Physical properties of amino acids
• Amiono acids as ampholytes
• Amino Acid contain both acidic (–COOH) and basic (–NH2) groups.
• They can donate a proton or accept a proton – hence Amino are
regarded as ampholytes.
• Zwitter ion (or dipolar ion) – [name zwitter is from German –
means hybrid].
• Is a hybrid molecule containing positive and negative ionic groups.
• The Amino Acid rarely exist in a neutral form with free carboxylic(–
COOH) and free amino [basic] (–NH2) groups.
• In strongly acidic pH (low pH), the amino acid is positively charged
(cation), while in strongly alkaline pH (high pH), it is negatively
charged (anion).
• Each AA has acharacteristic pH at which it carries positive and
negative charges and exists as zwitterions.

30. General structure of amino acid and its ion form

31. Existence of an amino acid as anion and zwitterion

32. I.Physical properties of amino acids
• Isoelectric pH (sympol pI) is difined as the pH at which a
molecule exists as a zwitterions or dopolar ion and carries
no net charge.
• Thus, the molecule is electrically neutral.
• The pI value can be calculated by taking the average
pKa values corresponding to the ionizable groups.

33. Titration curve of amino acid [Leucine]

34. II. Chemical properties of amino acids
• Amino acids with their acidic part form salts with
bases (e.g. with NaOH forming compouns like R–
COONa) and in reactions with alcohols they form
esters (–COOR)
• Amino acids undergo decarboxylation – to produce
corresponding amines.
• Reactions due to –COOH group
• this reaction assumes significance in the living cells
due to the formation of many biologically important
amines
• [histamine (from histidine), tyramine (from tyrosine),
γ-amino buteric acid (GABA) – from glutamate]

35. II. Chemical properties of amino acids
• Reaction with ammonia
• carboxyl group of dicarboxylic acids reacts with NH3 to
form amide
Aspartic acid + NH3 →
Asparagine
Glutamic acid + NH3 →
Glutamine
• Reactions due to – NH2 group
• The amino group behave as base and combine with
acids (eg. HCl) to form salts (–NH3Cl )

36. II. Chemical properties of amino acids
• Reaction with ninhydrin.
• The α-amino acids react with ninhydrine to form a
purple, blue, or pink colour complex (Ruhemann’s
purple)
• This reaction used for the quantative determination of
amino acids and protein.
• Proline and Hydroxyproline give yellow color with
ninhydrin.
• Transamination – very important reaction in amino acid
metabolism – based on transfer of an amino group from
an amino acid to keto acid to form a new amino acid
• Amino acid in reaction of oxidative deamination –
liberate free ammonia

37. Color reactions of proteins/amino acids
These test are used to identified amino acids