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Ch_322b_24.06 - Amino Acid Sequence of Polypeptides and...

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Amino Acid Sequence of Polypeptides and Proteins Structure Determination The different levels of structural information of a polypeptide or protein are similar to those of small molecules: The molecular weight (amu or Daltons) may be determined by several physical measurements such as ultracentrifugation, light scattering, gel electrophoresis, or mass spectroscopy. Important breakthroughs in techniques in recent years (such as electrospray ionization) have made mass spectroscopy an almost routine, but powerful, methodology for molecular weight determination. (1) The amino acid composition (analogous to elemental composition for small molecules) may be determined by classical chemical methods (complete hydrolysis and separation). (2)
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The Primary Structure The sequence of amino acids may be determined by older automated chemical, or newer mass spectroscopic, methods. The amino acid sequence of a polypeptide is the primary structure . (3) The primary structure is written left to right starting with the N-terminal residue and ending with the C-terminal residue. example: a tripeptide of glycine, alanine and phenylalanine H 3 NCH 2 C NHCHC NHCHCO 2 - + CH 3 CH 2 C 6 H 5 O = O = N-terminal residue C-terminal residue Gly.Ala.Phe Sequence information of a polypeptide is given by writing the amino acid residues in order from left to right as shown.
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