Classification of Amino Acid

Classification of Amino Acid


CLASSIFICATION OF AMINO ACID

INTRODUCTION

  • Amino acids are basic unit of protein
  • Contain an amino group and carboxyl group (except proline).
  • Unique side chain bonded to alpha carbon distinctly differentiates amino acid.
  • Amino acids having an asymmetric carbon atom exhibit optical activity.
  • Glycine is the simplest amino acid and has no asymmetric carbon atom and shows no optical activity.

Amino acid can be classified in 4 ways:

  • Based on structure
  • Based on polarity
  • Based on ability of body to synthesize
  • Based on metabolism

CLASSIFICATION BASED ON STUCTURE 

  • Aliphatic Side Chains : Glycine, Alanine, Valine, Leucine, Isoleucine
  • Side Chains Containing Hydroxyl (OH) Groups  :Serine, Threonine, Tyrosine
  • Side Chains Containing Sulphur Atoms  :Cysteine, Cystine, Methionine
  • Side Chains Containing Acidic Groups or their amides  : Aspartic acid, Asparagine, Glutamic acid, Glutamine
  • Side Chains Containing Basic Groups  : Arginine, Lysine, Histidine
  • Containing Aromatic Rings  : Phenylalanine, Tyrosine, Tryptophan(photochromosity seen in this group.)
  • Imino acids or heterocyclic amino acids : – One of the 20 amino acids, proline is an imino (-NH) acid not an amino (-NH2) acid, as are other 19. 

CLASSIFICATION BASED ON POLARITY

  • Cell membrane has its hydrophobic ends in the centre of membrane while its hydrophilic ends lie on the outer surface of membrane.
  • Hydrophobhic or Non polar aminoacid are present in transmembrane region.
  • Hydrophillic or polar amino acids are present on outer surface of membrane.

Polar Amino Acids (Hydrphilic)
a. Charged

  • Acidic Amino acids-Aspartic Acid (Aspartate), Glutamic Acid (Glutamate)
  • Basic Amino Acids-Histidine, Arginine,Lysine

b. Uncharged

  • Aliphatic amino acid with hydroxyl group as side chain: Serine, Threonine
  • Aliphatic amino acids with amide group: Asparagine, Glutamine
  • Simple Amino acid: Glycine alone
  • Sulfur containing Aminoacid: Cysteine alone. 

Nonpolar Amino Acids (Hydrophobic)                                                

  • Simple amino acid: Alanine alone
  • Sulfur containing amino acid: Methionine alone
  • Aromatic Amino acids except Histidine .
  • All branched chain amino acids: Leucine(most non polar),Isoleucine and Valine
  • Imino acid: Proline 

CLASSIFICATION BASED ON ABILITY OF BODY TO SYNTHESIZE

Essential

  • Eight of these amino acids are essential (or indispensable) and cannot be produced by the body.
  •  Leucine, Isoleucine, Lysine, Threonine, Methionine, Phenylalanine, Valine, Tryptophan

Nonessential

  • Asparagine, Alanine, Arginine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Proline ,Glycine, Tyrosine, Serine

Semi-essential

  • Histidine and Arginine

CLASSIFICATION BASED ON METABOLISM

  • Ketogenic :Leucine, Lysine
  • Glucogenic:Valine, Cysteine, Serine,Alanine, Histidine,Threonine, Arginine, Glycine, Glutamate, Proline/Hydroxy proline
  • Both Glucogenic & Ketogenic :Isoleucine, Tyrosine ,Tryptophan , Phenylalanine 

AMINO ACID

CLASSIFICATION

SPECIAL Products

Isoleucine

Ketogenic+Glucogenic/Essntl/Aliphatic

 

Valine

Glucogenic/Essntl/Aliphatic(neutral)

 

Leucine

Ketogenic/ Essntl/Aliphatic(neutral)

 

Lysine

Ketogenic/ Essntl/Basic

Carnitine

Methionine

Glucogenic/Essntl/Sulphur(neutral)

Creatine, epinephrine, poiyamines

Phenyl alanine

Ketogenic+Glucogenic/Essntl/aromatic(neutral)

 

Threonine

Glucogenic/Essntl/Aliphatic(neutral)

 

Tryptophan

Ketogenic+Glucogenic/ Essntl/aromatic(neutral)

NAP, NADP, serotonin, melatonin

Alanine

Glucogenic/Non-Essntl/Aliphatic(neutral)

Coenzyme-A

Glycine

Glucogenic/ Non-Essntl/ Aliphatic(neutral)

Creatine, glutathione, heme, purines, conjugated bite acids

Serine

Glucogenic/Non-Essntl/ Aliphatic(neutral)

Phosphatidyt serine, sphingomyelins, choline

Cystiene

Glucogenic/Non-Essntl/Sulphur(neutral)

Glutathione, taurine, co enzyme-A, active sulfate

Tyrosine

Ketogenic+Glucogenic/ Non-Essntl/Aromatic(neutral)

Thyroxine, epinephrine, nor epinephrine, dopamine, melanin

Valine

Glucogenic/Non-Essntl/Aliphatic(neutral)

 

Proline

Glucogenic/Non-Essntl/Heterocyclic

 

Glutamate

Glucogenic/Non-Essntl/Acidic

GABA, glutathione, gamma- carboxy glutamate

Asparagine

Glucogenic/Non-Essntl/acidic

 

Glutamine

Glucogenic/Non-Essntl/acidic

 Purines, pyrimidines, amino sugars

Arginine

Glucogenic/Semi-essntl/basic

Creatine , nitric oxide

Histidine

Glucogenic/Semi-essntl/Imidazole ring

Histamine

 Limiting amino acid

  • Insufficient in food.
  • Wheat-lysine (the most deficient) and threonine (second limiting amino acid)
  •  Rice-lysine
  • Legumes-tryptophan or methionine (or cysteine)
  • Maize-lysine and tryptophan

Isoelectric pH,

  • In isoelectric ph an amino acid is in zwitterion form (dipolar molecule), i.e. has both positive and negative charge on same acid.
  •  Overall molecule is electrically neutral

Important chemical reactions of amino acids

Reaction used to determine amino acid sequence in polypeptide chain.

  • Sanger’s reaction : – Uses Sanger’s reagent ( 1 -fluoro-2,4-dinitrobenzene) to tag amino terminal.
  • Edman’s reaction : – Uses Edman’s reagent (phenylisothiocyanate) to tag amino terminal.

Reaction used to identification of individual or group of amino acids

  • Ninhydrin test: – All amino acids.
  • Xanthophoretic reaction : – Aromatic amino acidse (Tyrosine, tryptophan, phenylalanine).
  • Millan’s teste (Millon-Nasse reaction) : – Tyrosine° (phenol group of tyrosine). Therefore millon’s test is positive in tyrosinosis°.
  • Aldehyde test : – Tryptophan (indole ring)
  • Hopkins-tole reaction : – Tryptophan (indole ring)
  • Sakaguch’s reaction : – Arginine (guanidinium group of arginine).
  • Sulphur test : – Cysteine (sulphydryl group)
  • Nitroprusside test : – Cysteine (sulphydryl group)
  • Pauly’s test : – Histidine (imidazole group)
  • Biuret reaction : – Peptide bond
  • Diazo reaction (Pauli’s) : – Histidine or tyrosine.
Exam Question
 
  • Amino acids having an asymmetric carbon atom exhibit optical activity.
  • Glycine is the simplest amino acid and has no asymmetric carbon atom and shows no optical activity
  • Aliphatic Side Chains : Glycine, Alanine, Valine, Leucine, Isoleucine
  • Side Chains Containing Hydroxyl (OH) Groups  :Serine, Threonine, Tyrosine
  • Side Chains Containing Sulphur Atoms  :Cysteine, Cystine, Methionine
  • Side Chains Containing Acidic Groups or their amides  : Aspartic acid, Asparagine, Glutamic acid, Glutamine
  • Side Chains Containing Basic Groups  : Arginine, Lysine, Histidine
  • Containing Aromatic Rings  : Phenylalanine, Tyrosine, Tryptophan(photochromosity seen in this group.)
  • Imino acids or heterocyclic amino acids : – One of the 20 amino acids, proline is an imino (-NH) acid not an amino (-NH2) acid, as are other 19.
  •  Cell membrane has its hydrophobic ends in the centre of membrane while its hydrophilic ends lie on the outer surface of membrane.
  • Hydrophobhic or Non polar aminoacid are present in transmembrane region.
  •  Hydrophillic or polar amino acids are present on outer surface of membrane.
  • Sulfur containing Aminoacid: Cysteine alone.                                        
  • Simple amino acid: Alanine alone
  • Sulfur containing amino acid: Methionine alone
  • Aromatic Amino acids except Histidine .
  • All branched chain amino acids: Leucine(most non polar),Isoleucine and Valine
  • Imino acid: Proline
  • Eight of these amino acids are essential (or indispensable) and cannot be produced by the body.
  •  Leucine, Isoleucine, Lysine, Threonine, Methionine, Phenylalanine, Valine, Tryptophan
  • Nonessential- Asparagine, Alanine, Arginine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Proline ,Glycine, Tyrosine, Serine
  • Semi-essential- Histidine and Arginine
  • Ketogenic :Leucine, Lysine
  • Glucogenic:Valine, Cysteine, Serine,Alanine, Histidine,Threonine, Arginine, Glycine, Glutamate, Proline/Hydroxy proline
  • Both Glucogenic & Ketogenic :Isoleucine, Tyrosine ,Tryptophan , Phenylalanine 

AMINO ACID

CLASSIFICATION

SPECIAL PRODUCTS

Isoleucine

Ketogenic+Glucogenic/Essntl/Aliphatic

 

Valine

Glucogenic/Essntl/Aliphatic(neutral)

 

Leucine

Ketogenic/ Essntl/Aliphatic(neutral)

 

Lysine

Ketogenic/ Essntl/Basic

Carnitine

Methionine

Glucogenic/Essntl/Sulphur(neutral)

Creatine, epinephrine, poiyamines

Phenyl alanine

Ketogenic+Glucogenic/Essntl/aromatic(neutral)

 

Threonine

Glucogenic/Essntl/Aliphatic(neutral)

 

Tryptophan

Ketogenic+Glucogenic/ Essntl/aromatic(neutral)

NAP, NADP, serotonin, melatonin

Alanine

Glucogenic/Non-Essntl/Aliphatic(neutral)

Coenzyme-A

Glycine

Glucogenic/ Non-Essntl/ Aliphatic(neutral)

Creatine, glutathione, heme, purines, conjugated bite acids

Serine

Glucogenic/Non-Essntl/ Aliphatic(neutral)

Phosphatidyt serine, sphingomyelins, choline

Cystiene

Glucogenic/Non-Essntl/Sulphur(neutral)

Glutathione, taurine, co enzyme-A, active sulfate

Tyrosine

Ketogenic+Glucogenic/ Non-Essntl/Aromatic(neutral)

Thyroxine, epinephrine, nor epinephrine, dopamine, melanin

Valine

Glucogenic/Non-Essntl/Aliphatic(neutral)

 

Proline

Glucogenic/Non-Essntl/Heterocyclic

 

Glutamate

Glucogenic/Non-Essntl/Acidic

GABA, glutathione, gamma- carboxy glutamate

Asparagine

Glucogenic/Non-Essntl/acidic

 

Glutamine

Glucogenic/Non-Essntl/acidic

Purines, pyrimidines, amino sugars

Arginine

Glucogenic/Semi-essntl/basic

Creatine , nitric oxide

Histidine

Glucogenic/Semi-essntl/Imidazole ring

Histamine

Don’t Forget to Solve all the previous Year Question asked on Classification of Amino Acid

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