Fundamentals of Biochemistry Third Edition Donald Voet • Judith G. Voet • Charlotte W. Pratt Chapter 2 Water Copyright © 2008 by John Wiley & Sons, Inc.

Why is Water Important? Most biological molecule’s shapes are influenced by physical & chemical properties of water Most biochemical reactions take place in water Water, or components of water participate in many biological reactions

Section 1 – Physical Properties of Water

Hydrogen bonding is very important in explaining the properties of water. Each water molecule can make up to 4 hydrogen bonds

Solid water Liquid water

Table 2-1

Why do nonpolar substance not like water?

Emulsions and Surfactants Emulsion: One liquid suspended in fine droplets in another liquid which to not mix. Ex: oil and water Salad dressing Mayonnaise Emulsifier: a chemical liaison between two incompatible liquids to make them stable, typically a surfactant Surfactant: agents that lower the surface tension of a liquid – amphiphilic – love’s both, contains both a polar and non-polar group

Surfactants Detergents Foaming agents Fabric softener Defoaming agents Emulsifiers Paints Adhesives Inks Anti-fogging Soil remediation Wetting Ski wax, snowboard wax Deinking (particularly during the enzymatic deinking of used paper during the recycling and repulping process) Foaming agents Defoaming agents Laxatives Agrochemical formulations Herbicides Insecticides Quantum dot coating Biocides (sanitizers) Hair conditioners (after shampoo) Spermicide (nonoxynol-9)

Types of surfactants Non-ionic – Used in drug delivery, cosmetics, and shampoos Ex: Fatty alcohols – drug delivery cocamide MEA – foaming agent in shampoo Anionic – Negatively charged head group, used in drug delivery, soaps, shampoos Ex: SDS – sodium dodecyl sulfate – protein separation, car soap, toothpaste, some aspirins Cationic – positively charged head group, aniseptics, herbicides Ex: Cetylpyridinium chloride (CPC) – antiseptic, mouthwash, anti-sore throat spray

Lipids, Water, and Disease Medical surfactant – surface active lipoprotein Coats outside of aveoli Important to inspiration Creates equal surface tension on all aveoli Aides in gas exchange Acts as a pollution filter http://trc.ucdavis.edu/biosci10v/bis10v/week10/alveolar.gif

Osmosis – The movement of WATER across a semipermeable membrane Diffusion – the movement of other stuff across a concentration gradient

Osmotic Pressure Osmotic Pressure = ∏ = the force required to resist water movement van‘t Hoff equation: ∏ = icRT ic = osmolarity of the solution i = number of solutes per molecule (NaCl = 2) c = concentration in molarity R = gas constant 8.315 J/mol T = temperature in Kelvin

Osmolarity in Biology Hypertonic: solution has a higher osmolarity than the cytosol Hypotonic: solution has a lower osmolarity than the cytosol

Practice Which of the following solutions has an osmolarity of 3? 3M Na3PO4 0.43M Na3PO4 0.75 M Na3PO4 3 M NaCl 1.5 M NaCl

Practice You want to isolate a lysosome to study it in the lab. Assuming that the only components inside a lysosome are KCl (0.1M) and NaCl (0.03M), how much sucrose (342 g/mol) do you need to make 1 liter of an isotonic solution to isolate the lysosomes?

Practice You want to isolate a lysosome to study it in the lab. Assuming that the only components inside a lysosome are KCl (0.1M) and NaCl (0.03M), how much glycogen (18,000 g/mol) do you need to make 1 liter of an isotonic solution to isolate the lysosomes?

Figure 2-14

Section 2 – Chemical Properties of Water

1 2 3

General acid reaction Abbreviated acid reaction Abbreviated acid reaction

4 5 6 Weak acids have pK > 1

7 8

Buffers are very important to biological systems Buffering capacity is +/-1 pH unit from the pK Different compounds have different buffering ranges

Practice What is the buffer concentration and pH of a mixture of 0.042M NaH2PO4 (pK = 6.86) and 0.058 M Na2HPO4?

Practice What is the pH of a mixture of 75 mL of 0.042M NaH2PO4 (pK = 6.86) and 150 mL of 0.058 M Na2HPO4?

Synthesis You are working in the lab and need to make a physiological phosphate buffer (pH=7.2). You have the following chemicals at your disposal: Phosphoric acid, monosodium phosphate, and disodium phosphate whose corresponding pKa’s are 2.15, 6.86, and 12.32. The molecular weight of each species is 98.0 g/mol, 119.98 g/mol, and 141.96 g/mol. Calculate the mass of each species that you would use to make a 100 mL of a 0.5M phosphate buffer at pH=7.2. Can complete all problems at the end of chapter two except for question 11.