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Bio 178 Lecture 3

Bio 178 Lecture 3. The Nature of Molecules & Chemical Building Blocks of Life. Reading. Chapters 2 & 3. ?. Quiz Material. Questions on P 34 & 60 Chapter 2 &3 Quizzes on Text Website (www.mhhe.com/raven7). Outline. Hydrogen bonds (cntd.) Water Acids, Bases, and Buffers.

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Bio 178 Lecture 3

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  1. Bio 178 Lecture 3 The Nature of Molecules & Chemical Building Blocks of Life

  2. Reading • Chapters 2 & 3 ? Quiz Material • Questions on P 34 & 60 • Chapter 2 &3 Quizzes on Text Website (www.mhhe.com/raven7)

  3. Outline • Hydrogen bonds (cntd.) • Water • Acids, Bases, and Buffers

  4. Hydrogen Bonds Properties • Weak and transient • 20X weaker than covalent • Directional • Because they are weak they are only effective over short distances. Importance • Stabilize the shape of many biological molecules • Form tight bonds when there are many

  5. Chemical Reactions Involve the breaking and formation of chemical bonds.

  6. Properties of Water *The polarity of water (and hence its ability to form hydrogen bonds) is responsible for its unique physical properties. • Cohesion and Adhesion Cohesion Eg. Surface Tension Adhesion Eg. Capillary action

  7. Heat Storage Water heats up slowly and maintains its temperature for long periods due to: (a) High Specific Heat • Measures amount of heat that must be absorbed/lost by 1 g of a substance to change its temp by 1 C. • Requires a lot of energy to break the hydrogen bonds so that water molecules can move freely and  increase temperature. • Importance - homeostasis. (b) High Heat of Vaporization • 586 calories are required to change 1 g liquid water into a gas. • Importance - sweating.

  8. Ice Formation Crystalline lattice  less dense than liquid water. Importance - barrier that protects aquatic life from cold air above. • Powerful Solvent Responsible for hydrophobic exclusion and  the shape of amphipathic molecules.

  9. Ionization of Water • Ionization Occurs when the covalent bonds within a water molecule break spontaneously: H2O  H+ + OH- • Moles The number of grams of a substance that contains 6.02 X 1023 molecules. Eg. 12 g carbon contains 6.02 X 1023 molecules of carbon. Molecular mass of C (mass per mole): 12 g

  10. Concentration Moles per liter = M Concentration of H+ in pure water at 25 C = 10-7 M • pH pH = -log[H+] Where log = exponent of [H+] Example - Neutral Solution What is the pH? pH = -log[H+] = -log(10-7) = -(-7) = 7

  11. N.B. pH is a logarithmic scale Example: How does the [H+] differ between a solution of pH 3 and 6 (how many times more concentrated is the solution of pH 3)? Acid A substance that dissociates in water to increase [H+]. Base A substance that combines with H+ when dissolved in water.

  12. Buffer A substance that minimizes changes in pH by acting as a reservoir for H+. Importance - Maintains pH of cells around 7.

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