Amino acids

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AMINO ACIDS

Transcript of Amino acids

Amino acids

Amino acids

ContentsINTRODUCTIONHISTORYCLASSIFICATIONSTRUCTUREPROPERTIESCONCLUSIONREFERENCES

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introductionAmino acids are a group of organic compounds containing two functional groups-amino and carboxyl. The amino group (-NH) is basic while the carboxyl group (-COOH) is acidic in nature.General structure of amino acidsThe amino acids are termed as -amino acids, if both the carboxyl and amino groups are attached to the same carbon atom. The -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 mostly exist in the ionized form in the biological system.

H

R-C-COO-

NH+3 H

R-C-COOH

NH2

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historyThe first amino acid which was discovered is asparagine in 1806. Threonine was the last amino acid to be found in the year 1938. All the amino acids have trivial or common name from which they were first isolated. Asparagine was found in asparagus and glutamine was found in wheat gluten: tyrosine was first isolated from cheese and glycine(greek glykos means sweet) was so named because of the sweet taste.4

Classification of amino acid

A) Nutritional classification of amino acidB) Classification of amino acid based on polarityC) Amino acid classification based on their metabolic fateD) Amino acid classification based on the structureE) Two main groups of amino acids

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a. Nutritional classification of amino acid1. Essential or indispensable amino acid2. Non-essential or dispensable amino acid

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1. Essential amino acidsThe amino acid which cannot be synthesized by the body and, therefore need to be supplied through the diet is called essential amino acids. Ten amino acids comes under this group.Arginine ,Valine , Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan 7

Arginine Lysine Histidine Valine Leucine Isoleucine Methionine Threonine Phenylalanine Tryptophan

NH-CH2-CH2-CH2 C=NH+2 NH2

CH2-CH2-CH2-CH2 - NH+3

-CH-COO- NH+3 H3C-CH OH

-CH-COO-

NH+3 H3C CHH3C

H3C CH-CH2H3C

CH3 CH2 CH H3C

-CH-COO-

NH+3 -CH-COO-

NH+3 -CH-COO-

NH+3 CH2-CH2

S-CH3

-CH-COO-

NH+3 -CH-COO-

NH+3 -CH2

-CH-COO-

NH+3 -CH2 N H

CH2 HN N

-CH-COO-

NH+3 8

2. Non essential amino acidsThe body can synthesize about 10 essential amino acids to meet the biological needs hence they need not be consumed in the diet. Glycine, Alanine, Serine, Cysteine, Aspartate, Asparagine, Glutamate, Glutamine, Tyrosine, and Proline.

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Glycine Alanine Serine Cysteine

Aspartic acid Asparagine Glutamate Glutamine

Tyrosine Proline

N CO

-CH-COO-

NH+3 H

-CH-COO-

NH+3

-CH-COO-

NH+3 -CH-COO-

NH+3 CH2SH

-CH-COO-

NH+3 -CH-COO-

NH+3 -CH-COO-

NH+3 -CH-COO-

NH+3 -OOC-CH2

H2N-C-CH2 O

-OOC-CH2-CH2

H2N-C-CH2-CH2 O

-CH-COO-

NH+3 HO- -CH2

H

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B. CLASSIFICATION OF AMINO ACIDS BASED ON POLARITY1. Non-polar amino acids with aliphatic R group2. Non-polar amino acids with aromatic R group3. Polar amino acids with no charge on R group 4. Polar amino acids with negative R group5. Polar amino acid with positive R group11

1. NON POLAR AMINO ACIDS with aliphatic r groupThese amino acids are non polar and also referred to as hydrophobic (water hating). They have no charge on the R group. The amino acids included in this group are Glycine, Alanine, Leucine, Isoleucine, Valine and Methionine2. Non polar amino acids with aromatic r groupTheir aromatic side chains are relatively nonpolar(hydrophobic). All can participate in hydrophobic interactions. The amino acids included in these groups are Phenylalanine, Tryptophan and tyrosine

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3. POLAR AMINO ACIDS WITH NO CHARGE ON R GROUPThese amino acids carry no charge on R group and are soluble in water or more hydrophilic. They possess group such as hydroxyl, sulfhydryl and amide groups. They participate in hydrogen bonding of protein structure. The amino acids in this group are- Proline, Serine, threonine, Cysteine, Glutamine and Asparagine4. POLAR AMINO ACID WITH NEGATIVE R GROUPThe dicarboxylic monoacid. Aspartic acid and Glutamic acid are included in this group.

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5. POLAR AMINO ACID WITH POSITIVE R GROUPThese amino acids carry positive charge on the R group and are dibasic monocarboxylic acid. They are highly basic in nature. The three amino acid Lysine, Arginine and Histidine are included in this group.

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C. Amino acid classification based on their metabolic fate1. Glycogenic amino acids2. Ketogenic amino acids3. Glycogenic and Ketogenic amino acids

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1. GLYCOGENIC AMINO ACIDSThese amino acids serve as precursors for the formation of glucose and glycogen. The amino acids included in this group are Alanine, Aspartate, Glycine, Methionine2. KETOgenic amino acidsFat can be synthezied from these amino acids. Two amino acids Leucine and Lysine are exclusively ketogenic.

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3. Glycogenic and ketogenic amino acidsThe four amino acids Isoleuciene, Phenylalanine, Tryptophan, Tyrosine are precursor for synthesis of glucose as well as fat.

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d. Amino acid classification based on the structure1. Amino acids with aliphatic side chains2. Hydroxyl group containing amino acids3. Sulfur containing amino acids4. Acidic amino acids and their amides5. Basic amino acids 6. Aromatic amino acids7. Imino acids

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Sl no.NamesymbolStructure3 letters1 letterI. AMINO ACIDS WITH ALIPHATIC SIDE CHAIN1.GlycineGlyG2.AlanineAlaA3.ValineValV

-CH-COO-

NH+3

-CH-COO-

NH+3 CH3

-CH-COO-

NH+3 H3C CHH3C19

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4.LeucineLeuL5.IsoleucineIleIII. AMINO ACID CONTAINING HYDROXYL (-OH) GROUP6.SerineSerS 7.

ThreonineThr T

-CH-COO-

NH+3 -CH-COO- NH+3

H3C CH-CH2H3C

CH3 CH2 CH H3C

-CH-COO- NH+3

-CH-COO- NH+3

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III. SULFUR CONTAINING AMINO ACIDS8.CysteineCysC9.MethionineMetMIV. ACIDIC AMIO ACIDS AND THEIR AMIDES10.Aspartic acidAspD11.AsparagineAsnN

-CH-COO-

NH+3

-CH-COO-

NH+3

-CH-COO-

NH+3 -CH-COO-

NH+3

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12.Glutamic acidGluE13.GlutamineGlnQv. Basic amino acids14.LysineLysK15.ArginineArgR

-CH-COO-

NH+3 -CH-COO-

NH+3 -CH-COO-

NH+3

-CH-COO-

NH+3 NH-CH2-CH2-CH2 C=NH+2 NH2

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16.HistidineHisHVI. AROMATIC AMINO ACIDS17.PhenylalaninePheF18.TyrosineTyrY19.TryptophanTrpW

-CH-COO-

NH+3 -CH-COO-

NH+3 -CH-COO-

NH+3

-CH-COO-

NH+3

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VI. Imino acid20.ProlineProP

N COO- H24

E. Two main groups of amino acids1. Standard amino acids2. Non standard amino acids

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1.STANDARD AMINO ACIDSAmino acids are building blocks of protein. The 20 standard amino acids also takes part in formation of protein structure.Arginine ,Valine , Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Glycine, Alanine, Serine, Cysteine, Aspartate, Asparagine, Glutamate, Glutamine, Tyrosine, and Proline.

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2. non-standard amino acidsIn addition to 20 standard amino acids, proteins may contain non-standard residues created by modification of standard residues already incorporated into a polypeptide.4-Hydroxyproline- derivative of Proline5-Hydroxylysine- derivative of Lysine6-N-Methyllysine-CarboxyglutamaeDesmosineSelenocysteine

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STRUCTURES OF NON-STANDARD AMINO ACIDS H COOH HO-C CH2 HOOC-CH-CH2-CH-COOH HSe-CH2 -CH-COOH H2C CH-COOH NH2 NH2 N H H H2N-CH2-CH-CH2-CH2-CH-COOH ch3-nh-ch2-ch2-ch2-ch2-ch-cooh OH NH2 NH2 .4-Hydroxyproline-CarboxyglutamateSelenocysteine5-Hydroxylysine6-N-Methyllysine

Desmosine28

Properties of amino acids The amino acids differ in their physiochemical properties which determine the characteristic of protein.A. Physical propertiesB. Chemical properties29

A. PHYSICAL PROPERTIES1. Solubility : Most of the amino acids are usually soluble in water and insoluble in organic solvents.2. Melting point : Amino acids generally melt at higher temperatures, often above 200C.3. Taste : Amino acids may be sweet (Gly, Ala, Val), tasteless (Leu) or bitter (Arg, Ile), Monosodium glutamate (MSG; ajinomotto) is used as a flavouring agent in food industry.

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4. Optical properties: All amino acids except glycine possess optical isomers due to the presence of asymmentric carbon atom. Some amino acids have a second assymmentric carbon e.g. isoleucine, threonine.

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5. Amino acids as ampholytes : amino acid contains both acidic(-COOH) and basic (-NH2) groups. They can donate a proton or accept a proton , hence amino acids are regarded as ampholytes.

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Cont6. Zwitterion or dipolar ion: it is a hybrid molecule containing positive and negative groups. The amino acids rarely exist in a neutral form with free carboxylic (-COOH) and free amino (-NH) groups. In strongly acidic pH(low pH), the amino acid is positively charged (cation) while in strongly alkaline pH (high pH), it is negatively charged (anion). Each amino acid has a characteristic pH (e.g. leucine, pH 6.0) at which it carries both positive and negative charge and exist as a zwitter ion.

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H

R-C-COO-

NH2 H

R-C-COOH

NH2 H

R-C-COO-

NH+3 H

R-C-COOH

NH+3 Amino acid Anion (high pH) Cation (low pH) Zwitterion (isoelectric pH)

H+H+H+H+EXISTENCE OF AMINO ACID AS CATION, ANION AND ZWITTERION34

Cont7. Isoelectric pH (symbol pI): the pH at which a molecule exists as a zwitter ion and carries no net charge making the molecule electrically neutral. The pI value can be calculated by taking the average pKa values corresponding to the ionizable groups. For example: leucine has two ionizable groups, and its pI can be calculated as follows. General formula- pk1(cOO-) + pk2 (NH+3) pH= ------------------------------ 2 For leucine- 2.4+9.6 pI= ---------- = 6.0 2 35

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Cont8. Titration of amino acids: The existence of different ionic forms of amino acids can be more easily understood by the titration curves. Example at low pH leucine exists as a fully protonated form as cation. As the titration proceeds with NaOH, leucine loses its protons and at isoelectric pH, it becomes a zwitterion. Further titration results in the formation of anionic form of leucine.

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pk1pk2pI38

pHEquivalents of NaOH

b. Chemical properties1. Reaction with ammonia: The carboxyl group of dicarboxylic amino acids reacts with NH3 to form amide Aspartic acid + NH+3 ------> Aspargine Glutamic acid + NH+3 -----> Glutamine2. The amino acid behave as bases and combines with acids (e.g. HCL) to form salts (-NH+3 Cl-).

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7. Reaction with ninhydrin : The - amino acids react with ninhydrin to form a purple, blue or pink colour complex (Ruhemanns purple). Amino acid + Ninhydrin ------> Keto acid + NH3 + CO2 + Hydrindantin Hydrindantin + NH3 + Ninhydrin ------> Ruhemanns purpleNinhydrins reaction is effectively used for the quantitative deamination of amino acids and proteins. (Proline gives yellow colour with ninhydrin).

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8. Colour reactions of amino acids : Amino acids can be identified by specific colour reactions.

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COLOUR REACTION OF AMINO ACIDSSL. NO.REACTIONSPECIFIC GROUP OR AMINO ACIDCOLOUR1. Xanthoproteic reactionBenzene ring of aromatic amino acids (Phe, Try, Trp)Yellow2. Millons reactionPhenolic group (Tyr)Red 3. Hopkins-Cole reactionIndole ring (Trp)Purple 4. Sakaguchi reactionGaunidino group (Arg)Red 5.Nitroprusside reactionSulfhydryl group (Cys)Bright red 6.Paulys testImidazole ring (His)Red

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conclusionAmino acids are at the basis of all life processes, as they are absolutely essential for every metabolic process.Among their most important tasks are theoptimal transport andoptimal storage of all nutrients (i.e., Water, fat, carbohydrates, proteins, minerals and vitamins).The majority of diseases such as obesity, high-cholesterol levels, diabetes, insomnia, erectile dysfunction or arthritis can essentially be traced back to metabolic disturbances. This also applies to hair loss and serious cases of wrinkle formation.The positive effects of amino acids on: Arthritis, Osteoporosis, Cholesterol, Diabetes, Fat-burning, Healthy skin, Hair loss, Sleep, Mind swings and Performance.

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TRANSPORT AND STORAGE OF WATER, FAT, CARBOHYDRATES, PROTEINS, MINERALS AND VITAMINSAmino acids

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references- david l. nelson and Michael m. cox, third edition, lehninger, principles of biochemistry - u. satyanarayana and u. chakrapani, third edition, biochemistry

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