Water. Definition: A mole (or mol ) Water can IONIZE transiently. NONpolar covalent molecules do not dissolve in water

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1 Today s Topics Polar Covalent Bonds ydrogen bonding Properties of water p Water C bonds are Nonpolar Will these molecules dissolve in water? Start Macromolecules Carbohydrates & Lipids Sept 4, 05 Why are they nonpolar? Time NNpolar covalent molecules do not dissolve in water Because they don t form hydrogen bonds Water can INIZE transiently ydronium ion ( 3 ) ydroxide ion ( ) nly a tiny fraction is ionized at any moment Definition: A mole (or mol ) Represents an exact number of molecules ne mole is 6.0x0 3 molecules Molarity Number of molecules per liter of solution Mass ydrogen atom =g/mole xygen atom= 6 g/mole Water ( )= 8g/mole

2 0 7 seconds since the big bang. 4 billion years x 3,557,600 seconds / year That is less than one millionth of a mole of seconds! ow big is a mol? 6.0 x 0 3 Define dissociation constant for water x0 7 M x0 7 M The product always equals x x 0 7 = 0 4 (so if []= x0 4 M, what is []?) x0 0 M p is a shorthand for the concentration of In pure water: [ ] = 0,000,000 = x 0 7 p = negative log of (an awkward number) p = 7 Figure 3.8 Increasingly Acidic [ ] > [ ] Neutral [ ] = [ ] Increasingly Basic [ ] < [ ] p Scale Battery acid Digestive (stomach) juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water uman blood Seawater Milk of magnesia ousehold ammonia ousehold bleach ven cleaner Low p abundant depleted Acidic igh p depleted abundant Basic Buffers resist changes in p C 3 donor (acid) C 3 acceptor (base) A <> A

3 CC bonds are very stable can make very long chains Carbon forms the backbone of most biological molecules C C C C C 3 3 C C C C C ydrocarbons contain only C and Can form chains or branched chains or rings Carbon can form covalent bonds with many different elements Fig. 49 Functional Groups determine the biological properties Estradiol Testosterone First Second Third ydrogen Lithium Beryllium 3 Li 4Be Boron Carbon 3 B 6C Nitrogen 7 N xygen 8 elium e Fluorine 9 F Neon 0Ne Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon Na Mg 3 Al 4 Si 5 P 6 S 7 Cl 8 Ar Types of Functional Groups Know the functional groups in Fig..7, page 5 ydrophobic Straightchain Branchedchain ydrocarbons with double bonds ydrocarbon rings Aromatic rings Many sizes and shapes, but all of these are ydrophilic Polar things Alcohols Sulfhydryls Aldehydes Ketones Polar Ionizable Things Carboxylic (amines) Phosphate R hydroxyl RC= aldehyde keto RC carboxyl RN amino RP 4 phosphate RS sulfhydryl 3

4 Some Functional Groups can Dissociate to form Ions R hydroxyl RS sulfhydryl RC= aldehyde RC carboxyl RN amino RP 4 phosphate What determines whether acids & bases are ionized? p! Ionizable Functional Groups Carboxylic acid RC pk a 3 to 5 RC N RC RC N Each has a balance point Amine Understand the concept, but don t memorize this pk b 8 to Ionizable Functional Groups Carboxylic acid RC pk a 3to5 RC N RC RC N Amine Understand the concept, but don t memorize this What happens when p = 7.0? pk b 8to ily Amines in fish Monomer cadaverine putrescine igh p Little N molecular form insoluble Low p Lots of N 3, ionized soluble 4

5 ydrolysis Monosaccharides Simple sugars can be coupled together by = Maltose C C C C C C C 4 glycosidic 4 linkage Maltose C C glycosidic linkage C Simple sugars can be coupled together by C C Formation of linkage C C C Fructose Sucrose C Fructose = Sucrose Fructose Sucrose Sucrose is a common disaccharide; Fructose Cellulose Fig. 57bc 0 µm 0.5 µm Starches: α glycosidic linkage down Cellulose molecules Cellulose: β glycosidic linkage up β monomer Fig. 58 5