Protein Structure and Pyrolysis of Amino Acids

Only certain a-amino acids are present in any protein structure, and they have the general formula R-CH(NH2)-COOH, with the exception of proline and hydroxyproline that have secondary amino groups. With few exceptions, amino acids have chiral molecules with L (S) configuration at the chiral a carbon  

The names and the structure of the a-amino acids present in proteins are shown in Table 12.1.1. Besides the amino acids that are protein constituents, many other amino acids occur naturally in living systems. Amino acids are linked in proteins through an amide bond (or peptide bond) formed between the amino group of one amino acid and the carboxyl group of the other amino acid. The peptide bond contains the planar group of atoms CaNCC. When a small number of amino acids are linked through F eptide bonds they form simple peptides (dipeptides, tripeptides, etc.). Long chains of amino acids are commonly named polypeptides. The sequence of amino acids in a polypeptide is known as primary structure. A polypeptide chain can be described schematically as follows  

Name Abbrev. Abbrev. Radical R connected to MW Formula 

Note whole formulas are shown for proline and hydroxyproline. 

Proteins are basically formed from one or more chains of polypeptides (with a particular primary structure). The chains of amino acids in proteins, being very long, can coil and fold. This spatial arrangement of amino acids is described by the secondary and tertiary structures of proteins. The arrangement of the amino acids that are near one another in the linear sequence is described by the secondary structure. For example, the amino acids may generate a helical structure (a-helix) such that the amino acids chain forms a tridimensional rod, and the amino acids that are four units apart can have hydrogen bonds between their N-H and C=0 groups. An example of a stereo view of an a-helix 

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