341lecture03sept14sakai

341lecture03sept14sakai - Cell Biology 341 Last lecture:...

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Cell Biology 341 Monday, Sept. 14, 2009 Today: Conclude noncovalent bonds: Van der Waals attractions and Hydrophobic forces Types of macromolecules Structures of amino acids and fatty acids Chapter 3 on protein structure Later this week: back to chapter 2 on catalysis Last lecture: chapter 2 Atoms share electrons in covalent bonds in order to complete their outermost electron shell Polar vs. nonpolar covalent bonds Hydrophobic vs. hydrophilic Noncovalent bonds: Ionic bonds Hydrogen bonds-effect on properties of aqueous solutions
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Hydrophilic molecules (polar bonds) will form H-bonds with water and with each other (ex: amino acids in proteins, the double helix of DNA, page 110) Hydrophobic molecules (nonpolar bonds) will not form H- bonds with water, resulting in low solubility (ex: octane, gasoline) A H(δ + ) in a highly polar bond can be reversibly released in aqueous solution as a proton. This proton will associate with water to form a hydronium ion (H 3 O + ) A molecule that donates a proton in aqueous solution is called an acid (example: HCl) • A molecule that accepts a proton is a base (example: -NH 2 ) Many biological molecules are weak acids, such as amino acids that contain a carboxyl group (-COOH) Weak acids are only partially dissociated in aqueous solution
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3. Van der Waals attractions These are the weakest interactions: 0.1kcal/ mole in aqueous solution Short-lived electrical attractions that occur
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This note was uploaded on 12/05/2009 for the course BIO 341 taught by Professor Noris during the Fall '09 term at Rhode Island.

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341lecture03sept14sakai - Cell Biology 341 Last lecture:...

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