lec8 fig - Figures for Lecture 8 - Protein Structure 10 Sep...

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Unformatted text preview: Figures for Lecture 8 - Protein Structure 10 Sep 2010 BIOL 231 (Be sure to also download the notes after lecture) I. Amino acids & the peptide bond The peptide bond is formed by reaction of the carboxyl group of one amino acid with the amino group of another. The bond is RIGID, and can’t be rotated around, so the =O and the –H on either side of the bond are always in trans, as shown. The four atoms in the yellow box lie in a single plane. On the next 4 pages are representations of the 20 common amino acids, adapted from figures in Karp’s Cell and Molecular Biology: -1- Non-polar or hydrophobic side chains are comprised mainly of C and H atoms, with few or no O or N atoms. Because their interaction with water is not favorable (remember hydrophobic forces), they will tend to be found buried in the interior of proteins, or in membrane-spanning regions of membrane proteins. -2- Polar uncharged side chains contain an O or N atom and have partial positive or negative charge. They interact favorably with water, they form H-bonds, and they can be highly reactive, like the serine side chains in the active sites of serine proteases. -3- Amino acids with charged side chains include the two acidic ones, aspartic and glutamic acid; the two basic ones, lysine and arginine. These four are always charged (+ or !) under physiological conditions (around neutral pH). This group also includes histidine, which has a pK close to neutrality. -4- Three amino acids , glycine, cysteine and proline, have unusual properties that make it useful for us to pull them out of their natural groups and look at them individually: The remaining pages illustrate some features of secondary and tertiary structure: -5- ...
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This note was uploaded on 09/18/2011 for the course BIOLOGY 231 taught by Professor Petethollenbeck during the Fall '10 term at Purdue.

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lec8 fig - Figures for Lecture 8 - Protein Structure 10 Sep...

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