ch369_f09_class_4_notes

ch369_f09_class_4_notes - Proteins (Chapter4oftextbook)

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“Proteins” (Chapter 4 of textbook) Some biological functions of  proteins: Enzymes - proteins that catalyze chemical reactions. Transport proteins - hemoglobin, myoglobin,  lipoproteins. Hormones - Insulin, human growth hormone.
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Single amino  acid. “R” group is  different, depending  on a.a. type. Examples of amino acids: alanine phenylalani ne serine 20 different amino acid types commonly occur in  proteins.
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Alanine, serine, phenylalanine.   Linked together by peptide bonds. peptide  bond Proteins typcially contain hundreds of a.a.  linked together. Proteins are polymers of amino acids,  linked together by “peptide bonds”.
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Not very soluble in water.  In proteins these a.a. are often  found buried in the interior, away  from water. Hydrophobic (or non-polar) amino  acids.
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Hydrophilic (or polar) amino  acids. More soluble in water. (includes the a.a. that can hydrogen bond  with water).
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These are very soluble in  water. Amino acids with positively charged side chain  (at pH 7). pK a  of arginine side chain =  about 12 pK a  of lysine side chain = about  10.5
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These are very soluble in  water. Negatively charged  a.a. (pK a  of side chains = about 4)
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What fraction of the Asp side chains are negatively  charged at pH 4?  At pH 7? Answers:   At pH 4, [conj. base] = [acid], so half the Asp side  chains have negative charge at pH 4.    At pH 7, [conj. base] / [acid] = 1000, therefore the large  majority of Asp side chains have a negative charge at pH 7.
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Amino acids are  chiral  (they can not be superimposed  on their mirror image). L-amino  acid D-amino  acid Proteins almost always consist of L-amino  acids. mirror
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A few amino acids with notable properties: Histidine at pH 7 is mostly: Histidine below pH 5 is  mostly: The ring of  histidine  has a pK a  of  about 6.
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Cysteine side chains  can link together to form a  disulfide bond ”. A protein with a disulfide  bond between two cysteines.
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chemicals (such as 2-mercaptoethanol) or specialized  proteins (such as thioredoxin). Protein with cysteines  in disulfide bond  (oxidized cysteines). +  2 HSCH
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This note was uploaded on 01/21/2010 for the course CH 369 taught by Professor Kbrowning during the Fall '07 term at University of Texas at Austin.

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ch369_f09_class_4_notes - Proteins (Chapter4oftextbook)

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