Amino Acids and Proteins Transparencies_1

Amino Acids and Proteins Transparencies_1 - Amino Acids and...

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Unformatted text preview: Amino Acids and Proteins I. Amino Acids and Peptides A. Relationship of Amino Acids to Proteins 1. Amino acids are the building blocks that make up proteins 2. 20 different amino acids function as building blocks B. Characteristics of Amino Acids 1. Contain Two Functional Groups a. Amino Group -NH 2 b. Carboxyl Group - COOH 62 2. Alpha Amino Acids - The carboxyl group and amino group are attached to the same carbon a. Most are primary amines 3. Alpha L- Amino Acids - All amino acids except for glycine have a chiral carbon and may exist either as L-amino acids or as D-amino acids H O H | || N - C *- C – O- H H | R 63 4. Imino acids (Proline and Hydroxyproline) - Are secondary amines having the imino group ( -NH- ) tied in a cyclic structure C. Names of Amino Acids, Classes, and Three letter abbreviations 1. See transparencies 64 65 66 67 68 2. Learn a. Categories and amino acids in them (aliphatic, aromatic, heterocyclic, Sulfur containing, basic, acidic, amides, and hydroxy-containing) b. Three letter abbreviation of each amino acid c. Names of special groups in some amino acids (Indole ring, Imidazole Ring, ε- amino group, guanido group) d. Structures of selected amino acids identified by the instructor D. Dipolar Nature of Amino Acids 1. Predicted properties on the basis that they are organic 69 a. Predict low melting point b. Predict low water solubility 2. Actual properties a. Have high melting points with charring rather than melting b. Highly water soluble 3. Due to Zwitterion - Dipolar Ion a. Show general formula of Zwitterion + 70 H 2 N- CH-COOH H 3 N-CH-COO – | | R R 4. Examples a. Ala + H 2 N- CH- COOH H 3 N-CH- COO – | | CH 3 CH 3 b. Ser + H 2 N- CH- COOH H 3 N-CH- COO – | | CH 2 OH CH 2 OH E. Acid Base Nature of Zwitterion 1. Reaction of Zwitterion with acid and calculation of net charge 71 + + H 3 N- CH-COO - + H + H 3 N-CH-COOH | | R R 2. Reaction of Zwitterion with base and calculation of net charge + H 3 N- CH-COO - + OH- H 2 N-CH-COO- + H 2 O | | R R 3. Amphoteric or amphiprotic 72 a. When a substance may react either as an acid or as a base b. Zwitterion form of amino acid is amphoteric 4. Zwitterions as buffers 5. Charge on amino acid depends upon the acidity or basicity of the solution (pH) 6. Isoelectric pH or pI 73 a. pH at which an amino acid has no net charge b. If pH = pI charge = 0 c. If pH <pI charge = + d. If pH > pH charge = - e. Other facts about the pI of amino acids 1. Each amino acid has its own characteristic pI - Not necessarily 7.0 2. pI of an amino acid depends upon the -R groups present (neutral, acidic, basic) 3. An amino acid is LEAST soluble at pH = pI 74 75 f. Exact behavior of amino acids in solution 76 Glutamic Acid 77 Glycine g. How to calculate net charge on amino acid in solution 78 Glycine + +-- NH 3 CH 2 COOH NH 3 CH 2 COO NH 2 CH 2 COO- At pH =1- At pH =12- At pH =6- At pH = pK 1 = 2.34- At pH = pK 2 = 9.6- pI = pK 1 + pK 2------------- 2 79 Aspartic Acid + +- +...
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Amino Acids and Proteins Transparencies_1 - Amino Acids and...

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