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Transcript
Proteins are built from 20 kinds of alpha-amino acids. 21st aa = selenocysteine “CO-R-N” clockwise When viewing down from H to C-alpha L-amino acid Free -SH group of cysteine: S S -Reacts readily with heavy metals -Easily oxidized pKa Three- and one-letter codes for amino acids Disulfide bond Insulin sequence Modified amino cid residues Rotation around this C-N bond is not free. Peptide unit: -Rigid -Usually trans -Dipole moment H These two bonds are free to rotate. 0.5+ 0.5Alpha-helix has a large dipole moment. Antiparallel beta-sheet Proteins: -Fibrous proteins eg. keratin, collagen, sil Collagen sequence -Globular proteins Collagen triple helix G, Gly Myoglobin is rich in alpha-helices. Ribonuclease: beta and alpha 4 disulfide bonds Hemoglobin: tetramer Beta-alpha-beta motif: The crossover connection is nearly always righthanded. Poliovirus: 60-mer Antibody light chain: beta-sandwich Ribonuclease sequence Refolding of proteins is very difficult. Proteins can be easily denatured. Conformational change is important for function.