This document provides an overview of amino acids, including their structure, classification, properties, and functions. It discusses that amino acids are the building blocks of proteins and there are 20 common amino acids. They are classified based on the composition of their side chains, number of amino and carboxyl groups, and polarity. Key points covered include their amphoteric nature, ionization states, titration curves, essential vs. nonessential amino acids, and roles in biochemical pathways and protein structure.

1. By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2.  INTRODUCTION
STRUCTURE
CLASSIFICATION OF AMINO ACIDS
ELEROCHEMICAL PROPERTIES
IONIZATION
TITRATION CURVE
NONSTANDARD PROTEIN AMINO ACIDS
NONPROTEIN AMINO ACIDS
DISTRIBUTION IN PROTEIN
ESSENTIAL AMINO ACIDS
FUNCTIONS

3.  Amino acids are the ‘Building block of Protein’.
Protein are polymers of amino acids, with each
amino acid residue joined to its neighbor
by a special type of covalent bond.
Protein can be broken down (hydrolyzed) to their constitution amino acids by
a variety of methods and earliest studies of proteins naturally focused on the
free amino acids derived from them.
Twenty amino acids are commonly found in protein.
The 1st discovered amino acid was Asparagine, in 1806.
The last amino acid was Threonine,which was not identified until 1938.

4. Each amino acid has a nitrogenous compound having both a carboxyl (-
COOH) & a amino group.
R strands for the side chains that are different for each amino acid.
R may be as a Hydrogen atom(H) or a methyl group(-CH3) or a more
complex structure.
The general structure of an alpha
amino acid.

5. The 1st carbon is the part of the carboxyl group & 2nd carbon is attached
to amino group, is known as α-carbon.
The α-carbon in all the amino acids is asymmetric except in Glycine.
Due to asymmetry, all amino acids show the two optical active form.
Those having NH3 group to right are designated as D-form & those having
NH3 group to the left as L-form.

6. Three system of classifying amino acids are in vogue
On the basis of the composition of the side chain or R group.
On the basis of the number of amino & carboxyl groups.
On the basis of polarity of the side chain or R group.

7. Simple amino acid:- no other functional group.
Ex- Alanine, Glysine, Valine, Leusine, Isoleusine
Hydroxy amino acid:- contain hydroxyl group
Ex- Serine, Threonine
Sulfur containing amino acid:-contain sulfur atom.
Ex- Cysteine, Metheionine
Acidic amino acid:-contain carboxyl group.
Ex- Aspartic acid, Glutamic acid
Basic amino acid:-contain amino group.
Ex- Lysine, Arginine
Amino acid amide:-carboxyl is transferred into amide.
Ex- Asparagine, Glutamine
Hetero cyclic amino acid:-
contain an atom other than carbon. Ex-Tryptophan,
Histidine, Proline
Aromatic amino acid:- contain a benzene ring.
Ex-Phenylalanine, tyrosine

8. Monoamino-monocarboxylic amino acid:- Having one amino Group
and carboxylic group.
Ex.- Glysine, Alanine, Leusine, Isoleusine, valine, Proline, Phenylalanine,
Tyrosine, Tryptophan, Metheionine, Serine, Threonine, Cysteine, Asparagine,
glutamine.
Monoamino- dicarboxylic amino acid:- Having one amino group and
two carboxylic group.
Ex.-Aspartic acid, Glutamic acid
Diamino- monocarboxylic amino group:- Having two amino group and
one carboxylic group.
Ex.- Lysine, Arginine, Histidine

9. CH3 CH COOH CH3 CH CH COOH
NH2 CH3 NH2
Alanine Valine
H CH COOH CH3 CH CH2 CH COOH
NH2 CH3 NH2
Glysine Leusine
CH3 CH2 CH CH COOH CH3 S CH2 CH2 CH COOH
CH3 NH2 NH2
Isoleusine Methionine
HS CH2 CH COOH
NH2 Cysteine

10. CH2 CH2 COOH CH3 CH CH COOH
OH NH2 OH NH2
Serine Threonine
NH2 NH2
O C CH2 CH COOH O C CH2 CH2 CH COOH
NH2 NH2
Asparagine Glutamine
H2C CH2
H2C CH COOH
NH Proline

11. CH2 CH COOH OH CH2 CH COOH
NH2 NH2
Phenylalanine Tyrosine
C CH2 CH COOH
CH NH2
N
H
Tryptophan

12. HOOC CH2 CH COOH
NH2
Aspartic acid
HOOC CH2 CH2 CH COOH
NH2
Glutamic acid

13. H2N CH2 CH2 CH2 CH2 CH COOH
NH2
Lysine
NH
H2N C NH CH2 CH2 CH2 CH COOH
Arginine NH2
HC C CH2 CH COOH
HN N NH2
C
H Histidine

14. Based on polarity of R- group, which have tendency to interact
with water molecules; R group polarity vary from non-polar &
hydrophobic to polar & hydrophilic
Classified into 5 categories-
a.Non-polar & aliphatic R-group amino acid
b. Non-polar & aromatic R-group amino acid
c. Polar & uncharged R- group amino acid
d. Positively charged R-group amino acid
e. Negatively charged R-group amino acid

15. Non-polar, aliphatic:- Positively charged:-
a. Alanine a. Lysine
b. Valine b. Arginine
c. Leusine c. Histidine
d. Isoleusine
e. Proline
f. Methionine Negatively charged:-
Non-polar, aromatic:- a. Aspartic acid
a. Phenylalanine b. Glutamic acid
b. Tryptophan
Polar, uncharged:-
a. Glycine
b. Serine
c. Threonine
d. Tyrosine
e. Cysteine
f. Asparagine
g. Glutamine

16.  Amino acids reacts with both acids and bases. So they are Amphoteric in
nature.
In acid solution coo- requires a proton and the amino acid become an
ammonium salt. Same in alkaline, the NH3+ ion loses proton and become the
anion of a salt.
These reaction are of reversible in nature & depends on the pH of the medium.

17. The α-COOH & α-NH3 are ionized in solution at physiological pH with the
deprotonated –COO¯ group (-ve) & protonated -NH3+ (+ve) . Amino acid in its
dipolar state is called as Zwitter ion/Dipolar ion.
The point at which the molecules has equal
no. of the +ve & -ve charge is known as
Isoelectric point. At this amino acid does
not migrate in an electric field.
If pH is lower, the –COOH group ceases to
be ionized& the molecules become +vely
charged. (1) unionized and (2) zwitterionic forms
The dissociable COOH & NH2 are responsible
for the two characteristic pk value of amino acids. (pK1 for COOH & pK2 for
NH3+)

18. H H H
CH3 CH COOH CH3 CH COO¯ CH3 CH COO¯
pK1=2.34 pK2=9.69
NH3+ NH3+ NH2
Net charge= +1 Net charge= 0 Net charge= -1

19. Titration curve of Alanine:-
In the 1st stage of titration in which –
COOH loses proton , proton donor &
proton acceptor species are present.
The pH is equal to pKa of protonated
group that is 2.34.
As the titration proceeds another imp
point in reached at pH 6.02, where removal
of 1st proton is completed & removal of 2nd
proton has just begun.
At this pH, alanine as dipolar form, but
with no net charge.
The 2nd state of titration is to removal of
proton from –NH3+. The pH at this state is
9.69, which is equal to the pKa for –
NH3+.
The titration is completed at pH of 11.69.

20. Nonstandard amino acids are modification of the amino acids found in
protein, are formed by genetic code.
some of them given below-
a. Cystine:- formed by addition by linking of two cysteine molecules.
b. Hydroproline:- formed by addition of a hydroxyl group to proline;
constitute 12% of the composition of collagen.
c. Methyllysine:- modification of lysine, found in histones and myosin
a contractile protein of muscle.
d. Hydroxylysine:- also a component of collagen; 1% of total amino acids.
e. Carboxyglutamate:- found in blood clotting protein prothrombin.
In protein corn α-aminoadipate has been detected. It has one CH2 group
more than glutamic acid.
Another protein α-ε-diaminopimelate has been found in bacterial protein.

22. HOOC CH2 CH2 CH2 CH COOH
NH2
(α- aminoadipate)
HOOC CH CH2 CH2 CH2 CH COOH
NH2 NH2
(α,ε- diaminopimelate)

23. Approximately 300 amino acids have been found, which never
constituents of protein but which either play metabolic role or occur as
natural products.
a. Ornithine:- found in animal tissue & intermediate in biosynthesis of
urea.
b. β-Alanine:- isomer of alanine constituent of vita. Pantothenic acid.
c. γ- aminobutyric acid:- found in brain; formed by decarboxylation of
glutamic acid.
d. Creatine:- derivative of glycine , Imp. Constituent of muscle; plays
as imp. Role in storage of energy.
e. Citruline:- also intermediate in biosynthesis of urea.

24. H2N CH2 CH2 CH2 CH COOH H2N CH2 CH2 COOH
NH2
(ornithione) (β- alanine)
NH2 CH3
H2C CH2 CH2 COOH H2N C N CH2 COOH
NH
(γ- aminobutyrate) (Creatine)
NH2
O C HN CH2 CH2 CH2 CH COOH
NH2 (Citruline)

25. 40% by weight of fibroin & 25% by weight of collagen are account for
by glycine.
Fibroin is all rich in Alanine (30% by weight)
Collagen, gliadin & zein are rich in proline.
Human serum albumin with 585 amino acids residues has only one
tryptophan moiety.
The pulse are notable as they lack S-containing amino acid,
Methionine but contain basic amino acid Lysine; where as cereals lack
lysine but contain a sufficient amount of methionine.

26. Out of 20 amino acids(standard), 8 amino acids are called-
essential amino acids, because the human body can’t
synthesize them from other compound for their growth, so
they must be obtain from food.
Ex.- Leucine, Isoleucine, Lysine, Metheionine, tryptophan,
Valine, Threonine, Phenyalanine.
But cysteine, taurine, tyrosine, histidine & arginine are
semiessential for children because the metabolic pathway
that synthesize these amino acids are not fully developed.

27. The amino acids give rise to a variety of compounds:-
Formation of protein:-principle function of the amino acids is to form
protein by polymerization.
Antibiotics:- Non–protein amino acids are component of antibiotics.
Formation of amines:- amino acids form amines by losing carboxyl
group. Ex.-Histamine
Nitrogen storage:- the amino acid derivatives called amides serves as a
storage of nitrogen.
Biosynthetic pathway:- Non-protein amino acid participate in imp.
Biosynthesis pathway. Ex.- Ornithine & Citruline.
Formation of other compounds:-tyrosine produces the hormone
thyroxin & adrenalin & skin pigment melanin. Glycine forms heme.
Tryptophan produces vita. Nicotinamide & plant hormone IAA.

28. The 20 amino acid commonly founds as residuses in
protein contain α-carboxyl group, an α-amino group, and
a R-group substituted on the α-carbon atom.
The carbon atom of all amino acids except glycine is
asymmetric, and thus the amino acids can exist in at least
two steroisomeric forms.
 Amino acids are classified into five types on the basis of
the polarity and charge (at pH 7 ) of their R-groups.
Amino acids vary in their acid base properties and have
characteristics titration curves.

29.  LEHNIGER’S
BIOCHEMISTRY [DAVID L.NIKOLSON, MICHAEL M. COX]
(4th Edition) IBSN- 1403948763
FUNDAMENTALS OF BIOCHEMISTRY [J.L.JAIN, SUNJAY JAIN
& NITIN JAIN] (6th Revised Edition)
ISBN- 8121924537
TEXT BOOK OF BIOCHEMISTRY [THOMAS S. DEVLIN]
(6th Edition)
GENERAL MICROBIOLOGY [C.B.POWAR & H.F. DAGINAWALA]
(2nd Revised Edition)
NET:- google.co.in & wikipedia.in