This document discusses the classification of amino acids. It summarizes that amino acids can be classified into different categories based on their R-group structure, polarity, nutritional requirements, and catabolism. The key classifications covered include non-polar vs polar amino acids, essential vs non-essential amino acids based on nutritional needs, and glucogenic, ketogenic, or mixed amino acids based on their metabolic fates. The document also provides examples of amino acids that fall into each of these different classification groups.

1. CLASSIFICATION OF AMINO ACIDS
A.SEKHAR REDDY
20PIM3277
MS(PHARM) SEMESTER - II
(2020-2022)
DEPARTMENT OF
PHARMACOINFORMATICS
NIPER SAS NAGAR
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2. CONTENTS
1. INTRODUCTION TO AMINO ACIDS
2. INTRODUCTION TO PEPTIDE BOND
3. STRUCTURE OF AMINO ACIDS
4. CLASSIFICATION OF AMINO ACIDS
4.1. On the basis of R-group
4.2 .On the basis of Polarity
4.3. On the basis of Nutritional requirement
4.4. On the basis of Catabolism
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3. • Amino acids are the fundamental units of protein or
polypeptides
• A peptide is a short-chain made up of amino acid which,
together with other peptides, forms a protein
• Polypeptides with around 100 amino acids are then
considered proteins
• As many as 300 amino acids are found in nature but only 20
amino acids are standard as they are coded by genes (genetic
codes)
• Other non-standard amino acids are modified amino acids
and called non-protein amino acids
• Amino acids are colorless, crystalline solid which are
usually soluble in water but insoluble in organic solvent
• They are organic compounds having two functional groups;
one acidic carboxylic (-COOH) group and the other basic
amino (-NH2) group
Building blocks of proteins
INTRODUCTION TO AMINO ACIDS
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4. INTRODUCTION TO PEPTIDE BOND
• A peptide bond is a special type of amide bond formed
between two molecules where an α-carboxyl group of one
molecule reacts with the α-amino group of another molecule
releasing a water molecule
• A partial double bond exists between carbon and nitrogen of
the amide bond which stabilizes the peptide bond
• Thus, the resonance structure stabilizes the bond but also limits
the rotation around the amide bond due to the partial double
bond.
• Peptide bonds have a planar configuration that undergoes very
little movement around the C-N bond but the other single
bonds on either side of the C-N bond exhibit a high degree of
rotational motion.
• The C-N distance in a peptide bond is typically 1.33 Å, which
is intermediate between the values expected for a C-N single
bond (1.49 Å) and a C=N double bond (1.27 Å).
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5. Structure of Typical Amino acid
• The amino acids are termed as α-amino acids, if both the
carboxyl group and amino group are attached to the same
carbon atom.
• The α-carbon atom binds to a side chain represented by R
which is different for each of the 20 amino acids found in
proteins.
• The amino acids (except glycine) possess four different
groups (R, H, COO–, NH3+) held by α-carbon.
• Each amino acid is assigned a 3 letter or 1 letter symbol. E.g.
Glycine:- Gly or G
• Amino acids are ampholytes (having both negative and
positive charge) and exist in Zwitterion form.
• Only L- form of amino acids is found in proteins in human
body. D-form if present, is converted into L-form by
enzymes in liver.
STRUCTURE OF AMINO ACIDS
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6. Amino Acids
On the basis of R-
group (structure
and chemical
nature)
On the basis of
Polarity
On the basis of
Nutritional
requirement
On the basis of
Catabolism
(metabolic fate)
CLASSIFICATION OF AMINO ACIDS
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7. On the Basis of R-group
1. Amino acids with aliphatic side chains:
• Mono-amino, mono-carboxylic amino acids (simplest
amino acids)
• Glycine (G), Alanine (A), Valine (V), Leucine (L) and
Isoleucine (I)
• Valine, Leucine and Isoleucine are branched chain amino
acids (have branched aliphatic side chains)
2. Hydroxyl group containing amino acids:
• Contain –OH group in their side chain
• Serine (S), Threonine (T) and Tyrosine (Y)
• Tyrosine is usually considered under aromatic amino acids
3. Sulphur containing amino acids:
• Cysteine (with sulfhydryl group) and Methionine (with
thioether group)
4. . Imino acids:
• Contain imino (=NH) group instead of amino group
• Proline (P) having pyrrolidine ring, is an α-imino acid.
5. Acidic amino acids and their amides:
• Contain two carboxylic groups, hence called dicarboxylic
monoamino acids , Highly acidic in nature
• Glutamic acid (E) and Aspartic acid (D)
• Glutamine (Q) and Asparagine (N) are their respective
amide derivatives.
6. Basic amino acids:
• contain two amino groups, hence called dibasic
monocarboxylic acids, Highly basic in nature
• Lysine (K), Arginine (R) (with guanidine group) and
Histidine (H) (with imidazole ring )
7. Aromatic amino acids:
• Contain aromatic, cyclic ring like structure in the side
chain
• Phenylalanine (F), Tyrosine (Y) and Tryptophan (w) (with
indole ring)
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9. On the basis of polarity
1. Non-polar amino acids:
• Also called hydrophobic amino acids and have no
charge on the ‘R’ group
• Alanine, Leucine, Isoleucine, Valine, Methionine,
Phenyl alanine, Tryptophan and Proline
2. Polar amino acids with no charge on ‘R’ group:
• Carry no charge on R group but have polar groups
like hydroxyl, sulfhydryl and amide groups in them
• Glycine, Serine, Threonine, Cysteine, Glutamine,
Asparagine and Tyrosine
3. Polar amino acids with positive ‘R’ group:
• Dibasic monocarboxylic acids
• Lysine, Arginine and Histidine
• 4. Polar amino acids with negative ‘R’ group:
• Dicarboxylic monoamino acids
• Aspartic acid and Glutamic acid
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11. On the basis of nutritional requirement
• The 20 amino acids are required for the synthesis of variety of proteins, besides other biological functions.
However, all these 20 amino acids need not be taken in the diet.
1. Essential amino acids:
• These amino acids cannot be synthesized in our body, so these should be essentially present in diet.
• Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine,
Lysine are essential amino acids
• Arginine, however is a conditional amino acid (Essential for infants, non-essential for adults)
2. Non-essential amino acids:
• These amino acids can be synthesized in our body; hence, need not be included in diet.
• Glycine, Alanine, Serine, Cysteine, Asparagine, Glutamine, Aspartic acid, Glutamic acid, Tyrosine,
Proline
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12. On the basis of Catabolism (metabolic fate)
1. Glucogenic amino acids:
• These amino acids serve as precursors of gluconeogenesis (for glucose or glycogen synthesis)
• Glycine, Alanine, Methionine, Aspartic acid
2. Ketogenic amino acids:
• These amino acids breakdown to form ketone bodies for fat synthesis.
• Leucine and Lysine
3. Glucogenic and ketogenic amino acids:
• These amino acids breakdown to form precursors for both ketone bodies (fats) and glucose.
• Isoleucine, Phenylalanine, Tryptophan and Tyrosine
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