2.3 The two enantiomers of each amino acid defined by the a-carbon are designated D-and L-formsD for Dextrorotary, L for Levorotary) 2.3.1 The d- and L-forms of amino acids are named in reference to the absolute configuration of d and L- glyceraldehydes(whose structure was orignally assumed and confirmed by x-ray crystallography later). 2.3.2 Only the L-amino acids have been found in proteins D-isomers have been found only in small peptides of bacteria cell walls and in some peptide antibiotics). 2.3.3 The correlation of structure (or configuration) with optical rotation is very complex and has not been successful to date! (i. e, the D- and L do not tell anything about their optical rotation signs
2.3 The two enantiomers of each amino acid defined by the -carbon are designated D- and L- forms (D for Dextrorotary, L for Levorotary) 2.3.1 The D- and L-forms of amino acids are named in reference to the absolute configuration of Dand L- glyceraldehydes (whose structure was orignally assumed and confirmed by X-ray crystallography later). 2.3.2 Only the L-amino acids have been found in proteins (D-isomers have been found only in small peptides of bacteria cell walls and in some peptide antibiotics). 2.3.3 The correlation of structure (or configuration) with optical rotation is very complex and has not been successful to date! (i.e., the D- and L-signs do not tell anything about their optical rotation!)
2. 4 The amino acids ionize in aqueous solutions 2. 4.1 Crystalline amino acids (in neutral aqueous solutions) have melting points much higher than those of other organic molecules of similar size 2.4.2 The amino acids ionize to various states depending on ph values 2.4.3 The amino acids(of neutral side chains) exist predominantly as dipolar ions, known as zwitterions(German for hybrid Ions
2.4 The amino acids ionize in aqueous solutions. 2.4.1 Crystalline amino acids (in neutral aqueous solutions) have melting points much higher than those of other organic molecules of similar size. 2.4.2 The amino acids ionize to various states depending on pH values. 2.4.3 The amino acids (of neutral side chains) exist predominantly as dipolar ions, known as zwitterions (German for “hybrid ions”)
2.5 Each amino acid is given a three-letter abbreviation and a one-letter symbol. They often the first three letter and the first letter. When there is confusion an alternative is used. They must be remembered.(fig. 2.6 All proteins in all species(from bacteria to human) are constructed from the same set of 20 amino acids 2.6.1 All proteins, no matter how different they are in structure and function are made from the 20 standard amino acids 2.6.2 This fundamental alphabet of the protein language is at least two billion years old
2.5 Each amino acid is given a three-letter abbreviation and a one-letter symbol. They often the first three letter and the first letter. When there is confusion, an alternative is used. They must be remembered. (fig.) 2.6 All proteins in all species (from bacteria to human) are constructed from the same set of 20 amino acids. 2.6.1 All proteins, no matter how different they are in structure and function, are made from the 20 standard amino acids. 2.6.2 This fundamental alphabet of the protein language is at least two billion years old
COO COO HN HEC2NHs Coo COO cOO HaN-C-H H--C-NHs H N-C-H CH CH L-Alanine D-Alanine L-Alanine MaLanin LAlanne (a) c
COO COO HaNCH HGCHNH3 CH3 CH3 L-Alanine D-Alanine (a) Stryer's method walk from the amino group to the carboxyl group the hydrogen atom is on your left. L-Alanine
Stryer’s method: walk from the amino group to the carboxyl group, the hydrogen atom is on your left. L-Alanine