mcb450-5bf09 - Chapter 5 - Proteins: Primary Structure and...

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Unformatted text preview: Chapter 5 - Proteins: Primary Structure and Biological Function Fig. 5-CO, p. 93 Classes of Proteins • Fibrous (shape) – Tend to be water insoluble • Globular (shape) – Tend to be water soluble • Membrane (function) – Part of membrane structure Elements of Protein Structure • Primary – Sequence of amino acids in a protein • Secondary – Presence of regular elements • Tertiary – Knowledge of location in 3D of every atom in a protein • Quaternary – Presence of more than one polypeptide chain non- covalently associated Fig. 5-1, p. 94 Some Proteins Connective tissue protein Oxygen storage protein (a triple helix) Abundant in muscle Note helical regions Fig. 5-2, p. 94 Ribonuclease Primary Structure Fig. 5-3, p. 95 Secondary Structure Fig. 5-4, p. 96 Tertiary Structure Fig. 5-5, p. 96 Quaternary Structure – Hemoglobin Isolation and Separation of Proteins • Isoelectric precipitation – Proteins are least soluble, typically, at their isoelectric pH. – Reason is that there is no net charge on the protein at this pH, and molecules therefore do not repel one another. Fig. 5-7, p. 98 Table 5-1, p. 99 Typical Protein Purification Table Amino Acid Sequences • One wants to know the sequence of amino acids in a given protein. • There are several ways to accomplish this. Number of Possible Sequences • The number is enormous because there are 20 possible amino acid residues at each position in the polypeptide chain. • How many dipeptides are possible? • How many tripeptides are possible? Edman Degradation • Phenylisothiocyanate adds to the N terminal amino group of a peptide. • When the medium is made anhydrous and acid, a derivative of the N terminal residue is liberated and can be identified by mass spectrometry or gas chromatography. • Then the next N terminal residue may be identified by another such cycle. • Problem is that the yield drops off dramatically • Most powerful sequencing method Peptide Sequencing Strategy 1. The protein is purified to homogeneity....
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This note was uploaded on 01/27/2010 for the course MCB 450 taught by Professor Mintel during the Fall '07 term at University of Illinois at Urbana–Champaign.

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mcb450-5bf09 - Chapter 5 - Proteins: Primary Structure and...

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