BIO 201 Lecture Notes - Lecture 3: Chemical Formula, Cysteine, Protein Structure

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Molecules with the same chemical formula but different arrangement of atoms are isomers. Non-superimposable (i. e. non-identical), mirror image isomers can rotate polarized light; they are chiral. Chiral molecules are either left (levo;l) or right-handed (dextro;d) When carbon is bound to any 4 different atoms/groups, the molecule is chiral. All amino acids in proteins are left-handed (l) except glycine. Amino acids are defined by their side chains (r groups) Cooh (acidic so at ph7: special cases. C(cid:455)stei(cid:374)e: polar, (cid:271)ut (cid:272)a(cid:374) for(cid:373) (cid:272)ovale(cid:374)t (cid:862)disulfide(cid:863) (cid:271)o(cid:374)ds. Glycine: not chiral; non-polar, but not hydrophobic. Proline: r-group covalently bonded to backbone n! Oxidation -> cysteines form disulfide bonds with each other (usually extracellular) Polypeptides grow by addition of new amino acids onto cooh-end amino (n) terminus --------------------- carboxyl (c) terminus. Orientation of polypeptide can be determined by identifying. Primary (1): sequence of amino acids (n to c) Secondary (2)- a-helices and b-sheets: structure resulting from hydrogen bonding between functional groups on the polypeptide backbone.

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