Biochemistry 2280A Lecture Notes - Lecture 3: Alpha Helix, Beta Sheet, Peptide

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Biochemistry 2280 topic 3 protein structure. Because water is lost in formation of peptide bond, incorporated amino acids are called. Polypeptides elongated by adding to c-terminal end. Polypeptides written in n-terminal to c-terminal end: therefore backbone is ncc-ncc-ncc . Peptide bond appears like single bond but has some properties of double bond due to resonance between c-o and c-n bonds. Atoms are coplanar: therefore no free rotation around c-n axis, restricted folding patterns. Protein is minimum 50 amino acids: chains smaller than this are called peptides. Largest protein discovered is 30 000 amino acids long. Alpha helix: carbonyl and n-h groups oriented parallel to axis, each carbonyl group hydrogen bonded with n-h group four amino acids further, precisely 3. 6 residues per turn. Beta sheet: hydrogen bonds formed between neighbouring polypeptide strands lying side-by- side, can be parallel or anti-parallel, side chains protrude upwards and downwards of sheet. Other secondary structures include various loops, helices, and irregular conformations.

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