Amino acids Rgroups nonpolar acidic basic proteins condensation

Amino acids R-groups non-polar acidic basic proteins condensation between carboxylic acids and amines + carboxylic acid + H 2 O amine amide

Amides amides resonance structure dipeptide alanine glycine Ala-Gly +H 2 O

Polypeptides “backbone” _ _ _ H R H R _ H N 1 -C 1 -N 2 -C 2 -N 3 -C 3 - OH O O O peptide bonds C-terminal N-terminal residue = = = biological activity = structure 4 levels protein structure

Primary structure sequence of amino acids hemoglobin transports O 2 and CO 2 4 protein chains 300 amino acids Sickle cell anemia 6 th amino acid from N-terminus R Glu Val -CH 2 -CO 2 H -CH(CH 3)2 water soluble water insoluble

Primary structure study evolution -chain 146 residues horses - humans = 26 pigs - humans = 10 gorillas - humans = 1 1 successful change / 10, 000 years Primary structure - selective hydrolysis

Phe-Val-Asn-Gln-His-Leu-Cys His-Leu-Cys-Gly-Ser His-Leu-Val-Glu Gly-Ser-His-Leu-Val-Glu-Ala Phe-Val-Asn-Gln-His-Leu-Cys Leu-Val-Glu-Ala His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu

Secondary structure hydrogen bonding backbone groups = = = H-bond donors _ _ _ H R H R _ H N 1 -C 1 -N 2 -C 2 -N 3 -C 3 - OH O O O H-bond acceptors Two main secondary structures: -helix -sheet

Alpha helix Every C=O bonded to N-H 4 residues away forms a helix core is backbone R-groups outside 3. 6 amino acids per turn H proline = C O N no H-bonding breaks helix

Beta sheet Every C=O bonded to N-H far apart in 1 o structure on different chains peptide chains extended side-by-side maximal H-bonding for anti-parallel chains small R-groups above and below the sheet if not -helix or -sheet random coil

Secondary structure some proteins 1 o structure amino acid sequence 2 o structure -helix -sheet -helix silk collagen bone, teeth triple helices keratin hair, skin, wool, hooves cross-linked with disulfide bonds

Disulfide bonds cysteine -CH 2 -SH H H N C S-H C H H-S C N [O] reduced C H N C S S C N C C oxidized

Protein function enzymes biological catalysts immunoglobulins antibodies transport hemoglobin hormones regulation structural keratin, collagen motion actin, myocin function depends on structure