Peptide bond 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
phenyl etc. phenyl
Classification
according to the structure of the side chain and functional groups
according to side chain polarity
according to importance in human nutrition
essential = the human organism is unable to create them endogenously
conditionally essential = essential in the absence of precursors or immaturity of enzymatic systems
completely non-essential
cysteine threonine serine methionine aspartic acid
Extended classification
primary amino group 2 )
1 α-amino acid with a secondary amino group (-NH-) n=0, pyrrolidin
secondary amino group trivial names, systematic names, symbols (three-letter, one-letter)
Classification of essential amino acids
By side chain structure and functional groups
aliphatic with an unsubstituted chain
aliphatic hydroxyamino acids
aliphatic sulfur
with a carboxyl group in the side chain (monoaminodicarboxylic, acidic)
their monoamides (with a carboxamide group in the side chain)
with basic groups in the side chain
with an aromatic (heterocyclic) side chain
According to the polarity of the side chain and its ionic form (in a neutral environment)
non-polar, hydrophobic
Val, Leu, Ile, Phe, Tyr, Met, Pro;
sometimes Gly, Ala, Trp (amphiphilic)
glutamic acid 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
phenylalanine arginine lysine glutamine asparagine histidine tyrosine tryptophan proline L-cystine 4-hydroxy-L-proline 5-hydroxy-L-lysine 3-methyl-L-histidine O-phospho-L-serine sarkosine N,N,N-trimethylglycine L-carnitine
Representatives
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
Other non-protein 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
N,N-dimethylglycine
L-ornithin (n = 2)
L-citrulline (n = 2, karbamoylderivát ornithinu)
creatine-phosphate
Aromatic amino acids
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
S-alk(en)yl-L-cysteinesulfoxid S-alk(en)yl-L-cysteine ß-alanine L-ornithine L-citrulline creatine phosphate thyroxine DOPA
Physico-chemical properties
Physico-chemical properties
ion I1 (kation)
ion I2 (amfion)
ion I3 (anion)
free charge +1
free charge 0
free charge -1
pH < 2
pH ≈ 6
pH > 10
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
Organoleptic properties
sweet - Gly, Ala, Thr, Pro
acidic - Asp, Glu
bitter - Leu, Ile, Phe, Tyr, Trp
indifferent - others Unique properties = umami taste
Graph gly-ph L-amino acid D-amino acid L-isoleucine D-isoleucine L-allo-isoleucine D-allo-isoleucine sodium hydrogen glutamate Gly on pH
Links
Related articles
Sources
VELÍŠEK, Jan – HAJŠLOVÁ, Jana. Chemie potravin 2. 3. edition. 2009. ISBN 978-80-86659-17-6. SVAČINA, Štěpán – ET AL.,. Klinická dietologie. 1. edition. 2008. ISBN 978-80-247-2256-6.
