Classification and general structure of aminiacids

1. Biochemistry for medics
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NAMRATA CHHABRA,M.D.

2. Provide the monomer units from which the long
polypeptide chains of proteins are synthesized
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3.  L-amino acids and their derivatives participate in cellular
functions as diverse as:
 Nerve transmission and the
 Biosynthesis of porphyrins,
 Purines, pyrimidines, and urea.
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4.  Short polymers of amino acids called peptides perform
prominent roles in the neuroendocrine system as :
 hormones,
 hormone-releasing factors,
 neuromodulators, or
 neurotransmitters.
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5.  Each amino acid (except proline) has a carboxyl group, an
amino group and a distinctive side chain bonded to the
alpha carbon atom.
 At physiological pH the carboxyl group is dissociated
forming the negatively charged carboxylate ion(-COO-
),
and the amino group is protonated(-NH3
+)
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6. Amino acids can be classified in 4 ways:
1.Based on structure
2.Based on the side chain characters
3.Based on nutritional requirements
4.Based on metabolic fate
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7. 1) Aliphatic amino acids
They are classified in three broad categories:
 Mono amino mono carboxylic acids They are further
subdivided in 5 groups:
a. Simple amino acids-example: glycine, alanine
b. Branched chain amino acids-e.g.: valine,leucine,isoleucine
c. Hydroxyl group containing amino acids-e.g.: serine, threonine
d. Sulphur containing amino acids-e.g.: cysteine, cystine,
methionine
e. Amide group containing amino acids-e.g.-
asparagine,glutamine
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8.  Mono amino dicarboxylic acid
Example :aspartic acid, glutamic acid
 Di /poly amino mono carboxylic acid
Example : lysine, arginine
2) Aromatic amino acids
3) Heterocyclic amino acids
4) Imino acids
5) Derived amino acids
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9.  Simple amino acids: Glycine , Alanine
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10.  Branched chain amino acids: Valine, Leucine and
Isoleucine
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11. -OH group-containing amino acids: Serine and
Threonine
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12. Sulfur-containing amino acids: Cysteine, Cystine(Formed
by linking of two cysteine residues) and Methionine.
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13. Amide group-containing amino acids:
Glutamine and Asparagine
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14. Aspartic acid and Glutamic acid
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15. Arginine and Lysine
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16. Phenyl alanine and tyrosine
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17. Tryptophan and Histidine
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18. Proline
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19.  Non-α-amino acids
e.g.: β-alanine, γ-amino butyric acid (GABA), δ-amino Levulinic
acid
 Derived and Incorporated in tissue proteins:
e.g.: Hydroxy-proline, hydroxy-lysine
 Derived but not incorporated in tissue proteins:
e.g.: Ornithine, Citrulline, Homocysteine, Arginosuccinic acid
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20. A. Amino acids with a non-polar side-chain:
e.g.: Alanine, Valine, Leucine, Isoleucine, Phenylalanine,
Tryptophan, Proline
 Each of these amino acids has a side chain that does
not bind or give off protons or participates in
hydrogen or ionic bonds.
 Side chains of these amino acids can be thought of as
“Oily” or lipid like, a property that promotes
hydrophobic interactions.
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22. e.g. Serine, Threonine, Tyrosine, Cysteine, Asparagine and Glutamine.
 These amino acids are uncharged at neutral pH, although the side chains
of cysteine and Tyrosine can lose a proton at an alkaline pH.
 Serine , Threonine and Tyrosine each contains a polar hydroxyl group
that can participate in hydrogen bond formation.
 Side chains of Asparagine and Glutamine contain a carbonyl group and
amide group, they can also participate in hydrogen bond formation.
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24. a) Amino acids with a positively charged side-chain:
The basic amino acids- Lysine, Arginine and Histidine
b) Amino acids with a negatively charged side-chain:
The acidic amino acids- Glutamic acid and Aspartic acid
They are hydrophilic in nature.
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26. I. Essential amino acids:
These amino acids cannot be synthesized in the body and have to be present
essentially in the diet. Examples-
 Valine,
 Isoleucine,
 Leucine,
 Lysine,
 Methionine,
 Threonine,
 Tryptophan, and
 Phenylalanine.
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27. II. Semi-essential amino acids:
 These amino acids can be synthesized in the body but the
rate of synthesis is lesser than the requirement(e.g.
during growth, repair or pregnancy)
 Examples-Arginine and Histidine.
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28. III. Non-essential amino acids:
 These amino acids are synthesized in the body, thus their
absence in the diet does not adversely affect the growth.
Examples-
 Glycine,
 Alanine, and the other remaining amino acids.
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29. The carbon skeleton of amino acids can be used either for glucose
production or for the production of ketone bodies, Based on that
I.Both glucogenic and ketogenic amino acids:
 Isoleucine,
 Tyrosine,
 Phenylalanine and
 Tryptophan
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30. II. Purely Ketogenic amino acids:
 Leucine and
 Lysine
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31. II. Purely Glucogenic amino acids:
The remaining 14 amino acids are glucogenic-
 Alanine, Valine
 Serine, Threonine,
 Glycine, Methionine, Cysteine, Cystine,
 Asparagine, Glutamine,
 Aspartic acid, Glutamic acid,
 Histidine and Arginine.
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32. Of the over 300 naturally occurring amino acids, 20 constitute
the monomer units of proteins.
These 20 amino acids are called the Primary or Standard amino
acids.
Selenocysteine is the 21st Amino Acid
The other are Pyroglutamate and Pyrolysine.
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