21 amino acids which are characterized into essential and non-essential amino acids

1. Amino acids are organic compounds containing
amine (NH2)and carboxyl(-COOH) functional
groups ,along the side chain [R] specific to each
amino acid .
The key elements of amino acids are .C, H, O, N
Proteins on complete hydrolysis yield L-α-amino
acid . Therefore proteins are polymeres of L-α-
amino acid.

2.  As many as 300 amino acids occurs in nature .
Of these only 20 amino acids are known as
standard amino acid and are repeatedly found
in the structure of proteins.
 This is bcz of the universal nature of the genetic
code available for the incorporation of only 20
amino acids

3.  If a carbon atom is attached to four different
groups it is asymmetric and therefore exhibits
optical isomerism .
 The amino acids possess four different groups
[R,H,COO,NH3]held by α- carbon .thus all the
amino acids have optical isomers
 The structure of L- and D- amino acids are
written based on the structure of L- and D-
glyceraldehyde .

4. •Based on the structure and chemical nature , nutritional
requirement, metabolic fate they are classified as follows
1. Amino acid classification based on the structure
2. Amino acid Classification based on polarity
3. Amino acid classification based on nutrition
4. Amino acid classification based on their metabolic
fate

5. •Each amino acid is assigned a 3letter or 1 letter
symbol. These symbols are commonly used to
represent the amino acids in protein structure .
•The 20 amino acids found in proteins are divided
into seven distinct groups
I. Amino acids with aliphatic side chain
II. Amino acid containing hydroxyl [-OH] groups
III. Sulfur containing amino acids
IV. Acidic amino acids and their amides
V. Basic amino acids
VI. Aromatic amino acids
VII. Imino acid

6.  These are mono amino monocarboxylic acids .
This group consists of the most simple amino
acid .
A. GLYCINE Gly G
B. ALANINE Ala A

7. C. VALINE Val V
D.LEUCINE Leu L
E.ISOLEUCINE Ile I

8. A. SERINE ser S
B. THREONINE Thr T
C. TYROSINE Tyr Y

9.  Cysteine with sulfhydryl group and methionine
with thioether group are the two amino acids
incorporated during the course of protein
synthesis.
I. CYSTEINE Cys C
II. METHIONINE Met M

10.  Aspartic acid and glutamic acid are dicarboxylic
monoamino acids while asparagine and
glutamine are their respective amide derivatives
I. ASPARTIC ACID Asp D
II. ASPARAGINE Asn N
III. GLUTAMIC ACID Glu E
IV. GLUTAMINE Gln Q

12.  The three amino acids lysine , arginine and
histidine are dibasic monocarboxylic acids .
they are highly basic in character .
I. LYSINE Lys K
II. ARGININE Arg R
III. HISTIDINE His H

13.  Phenylalanine , tyrosine and tryptophan are
aromatic acids .besides these histidine may aslo
be considered under this category
I. Phenylalanine Phe F
II. Tyrosine Tyr Y
III. Tryptophan Trp W

14. Proline containing pyrrolidine ring is a unique amino
acid . It has an imino group instead of amino group
found in another amino acids . Therefore proline is an
α-amino acid
I. Proline pro P

15.  Amino acids are classified into four groups
based on their polarity .polarity is important
for protein structure
I. Non polar amino acids
II. Polar amino acids with no charge on R group
III. Polar amino acid with positive R group
IV. Polar amino acid with negative R group

16. •The 20 amino acids are required for the synthesis of variety
proteins , besides other biological functions .Based on the
Nutritional requirements, amino acids are grouped into two
classes
a) Essential amino acids
b) Non essential amino acids
Essential amino acids or indispensable amino acids:
• These amino acids are not synthesized by the body and
have to be taken through diet .
Ex : arginine , valine , histidine , isoleucine , leucine , lysine,
methionine , phenylalanine , threonine, trypthophan
• The two amino acids namely arginine and histidine can be
syntesized by adults and not by growing children and
hence considerded as semi-essential amino acids

17. Non essential amino acids : The amino acids which
are synthesized by our body. They are as follows:
Ex: glycine , alanine ,serine , cysteine , aspartate ,
aspargine , glutamate , glutamine , tyrosine and
proline .

18.  The carbon skeleton of amino acids can serve as
a precursor for the synthesis of glucose or fat or
both . From metabolic point of view , amino
acids are divided into three groups
I. Glycogenic amino acids :These amino acids can
serve as precursors for the formation of glucose
or glycogen
Ex: alanine , aspartate , glycine , methionine etc…

19. ii. Ketogenic amino acids: Fat can be synthesized from
these amino acids. Two amino acids leucine and lysine
are exclusively ketogenic
iii. Glycogenic and ketogenic amino acids : The four
amino acids isoleucine, phenylalanine , tryptophan ,
tyrosine are precursors for synthesis of glucose as well
as fat.

20.  Selenocysteine : In recent years the 21st amino
acid has been added . It is found at the active
sites of certain enzymes / proteins .
Ex: glutathione peroxidase , glycine reductase , 5-
deio-dinase , thioredoxin reductase .
 Selenocysteine is an unusual amino acid
containing the trace element of selenium in
place of the sulphur atom of cysteine
 Incorporation of selenocysteine into the
proteins during translation is carried out by the
codon namely UGA.
 UGA is a stop codon that terminates protein
biosynthesis .