Amino acids are the building blocks of proteins and thus a code of life. This slide discusses about the structure, importance and various classifications of amino acids.

1. Amino acids:
BuildingBlocks of Protein
By Abhishek giri
M.Sc –I / Sem – II
Paper – II

2. Points to consider
1. Structure
2.Classification
3.Properties
4.D-amino acids

3.  Amino acids are building blocks of proteins.
 Proteins are composed of 20 different amino acid (encoded by standard genetic code,
construct proteins in all species ).
 Their molecules containing both amino and carboxyl groups attached to the
same a-carbon (L-a-amino acids).
 Their chemical structure influences three dimensional structure of proteins.
 They are important intermediates in metabolism
 They can have hormonal and catalytic function.
 Several genetic disorders are cause in amino acid metabolism errors
What are Amino acids?

4. Louis-Nicolas VauquelinPierre Jean Robiquet
History of Amino acids
Isolated Asparagine in 1806

5. Basic structure
The basic structure of amino acids differ only in the
structure of the or the side chain (R-group).
L-isomer is normally found in proteins.
L-isomer

6. Classification
Amino acids are classified into different
ways based on :
A. Structure
B. Polarity
C. Nutritional requirement
D. Metabolic fate

7. A. Structure
 Based on Structure amino acids they are divided
into 7 distinct group
1. Amino acid with Aliphatic side chain:
2. Amino acid containing Hydroxyl group(-OH):
3. Amino acid containing Sulpur:
4. Acidic amino acid :
5. Basic amino acids:
6. Aromatic amino acids:
7. Imino acids:

8. 1.Amino acids withaliphaticsidechains:
Alanine(Ala)
Valine(Val)
Leucine(Leu)
Isoleucine(Ile)
Glycine (Gly)
Branched Chain
Amino acids

9. 2. (–OH)amino acids: 3. Sulfur amino acids:
Serine (Ser)
Threonine (Thr)
Tyrosine (Tyr)
Methionine
Cysteine (cys)
Cystine

10. 4.Acidic aminoacid
Asparagine (Asn)
Glutamine (Gln)Glutamic acid (Glu)
Aspartic acid (Asp)
Lysine (Lys) Arginine (Arg) Histidine (His)
5.Basic amino acid
Dicarboxylic
monoamino
acids

11. 6.Aromatic& Imino aminoacids
Tyrosine (Tyr)
Phenylalanine
Tryptophan (Trp)
Proline(Pro)
(=NH) Imino group
instead of Amino
group (-NH2)

12. B. Polarity
 Based on Polarity amino acids they are divided into
4 distinct group
1. Non- polar Amino acids:
2. Polar Amino acid with no charge on ‘R’ group:
3. Polar Amino acid with positive ‘R’ group:
4. Polar Amino acid with negative ‘R’ group:

13. 1.Nonpolar(Hydrophobic)R Groups
Proline (Pro)
Tryptophan (Trp)
Phenylalanine (Phe)
Methionine (Met)
Valine (Val)
Alanine (Ala)
Glycine (Gly)
Leucine (Leu)
Isoleucine (Ile)

14. 2.Polar (Hydrophilic)R Groups
Serine (Ser)
Cysteine (cys)
Glutamine (Gln)
Asparagine (Asn)
Tyrosine (Tyr)
Threonine (Thr)

15. 3.PositivelyCharged R Groups
Lysine (Lys) Arginine (Arg) Histidine (His)

16. Aspartic acid (Asp) Glutamic acid (Glu)
4.Negatively(Nonpolar) Charged RGroups
Two amino acids with negatively charged (i.e. acidic) side chains - Aspartate
(Aspartic acid) and Glutamate (Glutamic acid).
These amino acids confer a negative charge on the proteins of which they
are part.

17. C. Nutritional
 Based on Nutritional requirement amino acids are
divided into 2 distinct group
1. Essential or Indispensable Amino acids:
2. Non-essential or dispensable Amino acids:

18.  Required in diet
 Humans incapable of forming requisite
carbon skeleton
Arginine*
Histidine*
Isoleucine
Leucine
Valine
Lysine
Methionine
Threonine
Phenylalanine
Tryptophan
* Essential in children, not in adults
1.Essential AminoAcids in Humans
Semi-essential
amino acids

20. PVT TIM HALL

21.  Not required in diet
 Can be formed from a-keto acids by
transamination and subsequent reactions
Alanine
Asparagine
Aspartate
Glutamate
Glutamine
Glycine
Proline
Serine
Cysteine
Tyrosine
2.Non-EssentialAmino Acids in Humans

22. D. Metabolic fate
 Based on C-Skeleton of amino acids serve as a
precursor for the synthesis of Glucose or Fat or
both.
Form metabolic point of view they are divided into 3
groups
1. Glycogenic Amino acids:
2. Ketogenic Amino acids:
3. Glycogenic & Ketogenic amino acids:

23. 1. Glycogenic amino acids
Alanine (Ala)
Glycine (Gly) Methionine (Met)
Aspartic acid (Asp)

24. 2. Ketogenic aminoacids
Leucine (Leu) Lysine (Lys)

25. 3. Glycogenic & ketogenic Amino acids
Tyrosine (Tyr)
Isoleucine(Ile)
Phenylalanine
Tryptophan (Trp)

26. Properties ofAminoacids
 Amino acids differ in their physico-chemical
properties which ultimately determine the
characteristics of proteins.
A. Physical properties
B. Chemical properties

27. A. physical
PROPERTIES
Solubility Soluble in water but Insoluble in organic solvents.
Melting point Melts at Higher Temperature.
Taste Sweet (Gly, Ala, Val),
Tasteless (Leu),
Bitter (Arg, Ile), MSG.
Optical properties Optical isomers due to Asymmetric C-atom.
Amino acids as Ampholytes They can donate or accept a proton.

28. Nonionic and zwitterion forms of amino acids
The zwitterion predominates at
neutral pH
Weak acid
Weak base
Zwitterion = in German for “hybrid
ion”

30. Isoelectric pH
Defined as pH at which a molecule exists as a
Zwitterion & carries no net charge. Thus, the
molecule is electrically neutral.
pH = pK1 (COO⁻) + pK2 (NH3⁺)
2
pl = 2.34 + 9.60 = 5.97
2

31. Titrationof Amino Acids
Dipolar ionIzoelectric point
At the midpoint – pK=9.60. there is equimolar
concentration of proton donor and proton
acceptor
At the midpoint – pK1=2.34 there is
equimolar concentration of proton donor and
proton acceptor.

32. B. Chemical
 Reaction is mostly due to Functional groups namely
Carboxyl (-COOH) group & amino (-NH2) group.
 REACTION DUE TO (-COOH) GROUP :
 REACTION DUE TO (-NH2) GROUP :

33.  1.Amino acids forms Salts (-COONa) with bases &
esters (-COOR’) with alcohols.
 2. DECARBOXYLATON : amino acids undergo
decarboxylation to produce corresponding amines.
 3. REACTION WITH AMMONIA :
+ NH3
+ NH3
Aspartic acid (Asp)
Glutamic acid (Glu)
Asparagine (Asn)
Glutamine (Gln)

34.  4. The amino acids behaves as bases & combine with
acids (e.g HCL) to form salts (-NH3⁺Cl⁻)
 5. Colour reactions of Amino acids :
S.No. Test Significance
1) Ninhydrin reaction Given by all Alpha amino acids
2) Xanthoproteic test Given by aromatic amino acids
3) Millon’s test Confirmatory test for Tyrosine
4) Ehrlich’s reagent Confirmatory test for Tryptophan
5) Nitric acid test Given by throsine & tryptophan

35. 6.Ninhydrin Reaction
 This strong oxidizing agent
bring about the oxidative
decarboxylation of amino acid.
 Purple, Blue or Pink colour
complex is formed
(Ruhemann’s purple)
 Quantitative estimation of
amino acids & proteins

36.  7.Oxidative deamination : The amino acids undergo
oxidative deamination to liberate free ammonia.
 8.Transamination : Transfer of an α-amino group from
an amino acid to an α-keto acid to form a new amino
acid and a corresponding keto acid.

37. Uncommon Amino Acids
 Cell wall (plant)
 Collagen (connective tissue)
 Collagen
 Myosin
 Prothrombin (blood clotting)
 Ca2+ binding proteins
 Elastin
 A few proteins
 Incorporation
during
translation

38. D-Aminoacids
 Major amino acids are L-category, but certain D-
amino acids are also found in the antibiotics.
 Antibiotics like Actinomycin-D, Valinomycin,
Gramicidin-S.
D-serine
D-aspartate
D-Glutamic acid D-alanine
Brain Tissue
Bacteria cell
wall

39. Reference
 Biochemistry – U. Satyanarayana
 Advanced organic chemistry – Bahl n Bahl
 Principles of biochemistry – David L. Nelson
 A textbook on biochemistry – MN Chatterjee
 en.wikipedia.org/wiki/Amino_acid
 www.nlm.nih.gov/medlineplus/ency/article/002222.htm
 www.aminoacidsguide.com/
 www.imagerynet.com/amino/classification.html