Amino Acids (1.LF UK, NT)

- Amino acids are the basic building blocks of proteins. Chemically, they are organic compounds connected to each other by a peptide bond. At least one primary amino group –NH 2 and at the same time at least one carboxyl group –COOH must be present in the amino acid. Chemically, they are substituted derivatives of carboxylic acids.
 * 2–100 amino acids (monomers – peptides
 * 100 or more amino acids – proteins

More than 700 different AMKs have been demonstrated in nature. That is why we also divide AMK according to their occurrence:
 * amino acids found in all living organisms
 * bound in proteins (21 proteinogenic AMK), peptides or as free AMK
 * amino acids found only in some organisms
 * bound in peptides or as free AMK
 * they are not components of proteins

Proteinogenic amino acids, or coded ones, occur in proteins as L-alpha-amino acids (the exception is glycine). This is due to the chemical arrangement that is necessary for biogenic function. Specific types of amino acids, their sequence and spatial structure then give proteins their biological properties.

Structure

 * amino group (-NH2, free, substituted)
 * carboxyl group (-COOH)
 * other functional groups
 * hydroxyl -OH
 * sulfhydryl (mercapto group) -SH
 * sulphide -S-R
 * guanidylGuanidyl.jpg
 * phenyl etc. Fenyl.jpg

Classification
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 * according to the structure of the side chain and functional groups
 * according to side chain polarity
 * polar
 * non - polar
 * according to importance in human nutrition
 * essential = the human organism is unable to create them endogenously
 * valin, leucine, isoleucine, phenylalanine, lysine, methionine, tryptophan, threonine
 * conditionally essential = essential in the absence of precursors or immaturity of enzymatic systems
 * arginine, histidine
 * completely non-essential
 * Glycin.jpgne, alanine, serine, cysteine, aspartic acid a asparagine, glutamic acid and glutamine, selenocysteine, tysorine, prolineValin.jpgAlanin.jpg Leucinl.jpg Isoleucin.jpg
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 * AMK primární skup.jpg α-amino acid with a primary amino group (-NH2)
 * AMK primární skup.jpg α-amino acid with a primary amino group (-NH2)


 * 1 α-amino acid with a secondary amino group (-NH-)

n=0, pyrrolidin


 * AMK sekundární skup.jpg amino acids = chiral compounds of the L series
 * trivial names, systematic names, symbols (three-letter, one-letter)

Classification of essential amino acids
By side chain structure and functional groups According to the polarity of the side chain and its ionic form (in a neutral environment)
 * aliphatic with an unsubstituted chain
 * glycin, alanin , valin , leucin , isoleucin
 * aliphatic hydroxyamino acids
 * serin, threonin
 * aliphatic sulfur
 * cystein, methionin
 * with a carboxyl group in the side chain (monoaminodicarboxylic, acidic)
 * kyselina asparagová, kyselina glutamová
 * their monoamides (with a carboxamide group in the side chain)
 * asparagin, glutamin
 * with basic groups in the side chain
 * amino group
 * guanidyl group
 * imidazoyl cycle
 * lysin, arginin , histidin
 * with an aromatic (heterocyclic) side chain
 * fenylalanin, tyrosin , tryptofan , prolin
 * non-polar, hydrophobic
 * Val, Leu, Ile, Phe, Tyr, Met, Pro;
 * sometimes Gly, Ala, Trp (amphiphilic)
 * Glutamová kyselina.jpg, hydrophilic
 * Ser, Thr, Cys, Asp, Glu, Asn, Gln, Lys, Arg, His
 * Hydrophilic (according to the ionic form of the side chain in a neutral environment)
 * neutral (has no electrical charge): most
 * acidic (negative charge): Asp, Glu
 * basic (positive charge): Lys, Arg, His

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Derivatives of basic proteinogenic amino acids

 * the emergence of specific modifications
 * L-cystin (CySSCy)
 * 4-hydroxy-L-prolin (Hyp)
 * 5-hydroxy-L-lysin (Hyl)
 * 3-methyl-L-histidin
 * O-phospho-L-serine

N-substituted α-amino acids

 * N-methylglycin (sarkosin), N,N-dimethylglycin , N,N,N-trimethylglycin
 * L-carnitine (3-hydroxy-4-trimethylaminobutyrate, vitamin Bt)
 * ß-alanine (3-aminopropionová kyselina), γ-aminobutyric (4-aminobutyric) acid (GABA)

Sulfur amino acids

 * S-alk(en)yl-L-cysteiny, S-alk(en)yl-L-cysteinsulfoxidy



Basic amino acids and related compounds

 * L-ornithin (n = 2)
 * L-citrulline (n = 2, karbamoylderivát ornithinu)
 * creatine-phosphate

Aromatic amino acids

 * tetrajodthyronin (thyroxin), R = R1 = R2 = R3 = I
 * 3,4-dihydroxy-L-fenylalanin (DOPA)

Essential Amino Acids
foods deficient in certain amino acids
 * Lys − cereals (plant proteins in general)
 * Met − milk, meat
 * Thr − wheat, rye
 * Trp − casein, corn, rice

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Physico-chemical properties

 * acid-base (pK and pI)
 * optical
 * sensory

Acid-base properties (Gly)
Dependence of the ionic forms of Gly on pH

cation (I1) → amphion (I2) → anion (I3)

Optical properties

 * Gly = exception
 * majority = chiral atom Cα... 2 optical isomers (enantiomers)
 * some 2 chiral centers... Ile, Thr, Hyp, CySSCy

L- and D-amino acids, L-amino acids = (S)-stereoisomers,výjimka: L-cysteine ​​= (R)-stereoisomer

D-amino acids = (R)-stereoisomers

Content

Diastereoisomers of amino acids
 * L-amino acid ie.: (S)-amino acid
 * D-amino acid ie.: (R)-amino acid
 * L-isoleucine (2S, 3S)-isoleucine
 * D-isoleucine (2R, 3R)-isoleucine
 * L-allo-isoleucine (2S, 3R)-isoleucine
 * D-allo-isoleucine (2R, 3S)-isoleucine

Organoleptic properties

 * sweet - Gly, Ala, Thr, Pro
 * acidic - Asp, Glu
 * bitter - Leu, Ile, Phe, Tyr, Trp
 * indifferent - others

Unique properties = umami taste
 * natrium-hydrogen-glutamát


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Související články

 * Peptidy (1. LF UK, NT)
 * Bílkoviny (1. LF UK, NT)
 * Aminokyseliny, peptidy, bílkoviny (1. LF UK, NT)