ch369_sum10_class4_notes

ch369_sum10_class4_notes - Proteins (Chapter 4 of textbook)...

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Unformatted text preview: Proteins (Chapter 4 of textbook) Some biological functions of proteins: Enzymes - proteins that catalyze chemical reactions. Transport proteins - hemoglobin, myoglobin, lipoproteins. Fibrous & structural proteins - collagen, keratin. Hormones - Insulin, human growth hormone. Single amino acid. R group is different, depending on a.a. type. Examples of amino acids: alanine phenylalanine serine 20 different amino acid types commonly occur in proteins. 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. Not very soluble in water. In proteins these a.a. are often found buried in the interior, away from water. Relatively hydrophobic (or non-polar) amino acids. Relatively hydrophilic (or polar) amino acids. More soluble in water. (includes the a.a. that can hydrogen bond with water). 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 These are very soluble in water. Negatively charged a.a. (pK a of side chains = about 4) 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 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. Cysteine side chains can link together to form a disulFde bond. A protein with a disulFde bond between two cysteines. Reduction of disulFde bonds can be carried out by reducing agents (chemicals such as 2-mercaptoethanol, or specialized proteins such as thioredoxin). Protein with cysteines in disulFde bond (oxidized cysteines). + 2 HSCH 2 CH 2 OH SCH 2 CH 2 OH SCH 2 CH 2 OH H H Protein with reduced cysteines. 2-mercaptoethanol + Function of a protein depends on structure. Globular proteins- are usually water soluble, with hydrophobic interior. Fibrous proteins- insoluble bers, such as collagen & keratin. Hexokinase, from Wikipedia commons. glucose binding pocket. Hexokinase is a globular protein, with a structure that is suited for binding glucose, and catalyzing its conversion to glucose-6-phosphate. Keratin is an example of a brous protein: An alpha helix. Ribbon shows path of protein backbone....
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ch369_sum10_class4_notes - Proteins (Chapter 4 of textbook)...

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