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Chapter 3 - C hapter 3 P rote i nst he mac romo lecu les of...

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Chapter 3 Proteins—the macromolecules of the cell Proteins are linear polymers of amino acids. o More than 60 different AA are in the cell. o 20 different AA are used to synthesis proteins. Amino acids come in two stereochemistry, L-amino acid and D-amino acid. (Asymmetrical) o L-AA has an amino group on the left side of the carbon atom, and on the right side there is a carboxyl group. (naturally occurring form is the L-AA in protein) o D-AA has an amino group on the Right side of the carbon atom, and on the left side there is a carboxyl group. o All amino acids have a Hydrogen group and unique R group (can be any of the 20 different functional group) that give it a different property. There are total of nine non polar AA (Hydrophobic) There are total of six polar AA (Hydrophilic) There are total of five polar charged AA (Hydrophilic) Two of them are acidic Three are basic Nonpolar Glycine (Gly) is the simplest of all the amino acids. It only has a hydroxyl group in place of the R group.
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Proline (Pro) is called an imino acid (ring like structure); the side chain (R group) comes back and attaches to the backbone. Proteins are absorbed at 280nm because of the aroma tic rings. Ex phenylalanine. Polar Polar AA have no charge and are formed by polar covalent bonds (Electrons are not equally shared). (-)0—H(+){hydroxyl group) serine, threonine, and tyrosine (aromatic ring) (-)N—H(+) asparagine, and glutamine. S—H cysteine Our body can make most of the AA, but our body can’t make about 8 AA and we need to get this from our diet. This are called essential AA. Cysteine is the only AA that has a free SH group on it, it smells bad. Two AA comes together and forms covalent bond (strong peptide bond) by dehydration synthesis reaction. 2 AA (dipeptide) forms 1 covalent bond (peptide bond) 3 AA (tripeptide) coming together forms 2 covalent bonds Long chain of AA is called a peptide, it has any of the 20 naturally occurring AA, they are covalently linked together by peptide bonds. Primary Structure Sequence of the AA (determined by the DNA) linked together by strong covalent peptide bonds forming polypeptide. Very hard to break this bond and therefore very stable structure Secondary Structure Local regions of the primary structure (polypeptide) can come together and form secondary structure by forming weak hydrogen bonds (usually between carbonyl group and amide group). Most common type of secondary structure is alpha-helix and beta-sheets.
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Alpha-helix and beta-sheets can be broken by Glycine and Proline AA.
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