CHEM 430 CH 2

Flashcard maker : Lily Taylor
Why do polar biomolecules dissolve readily in water?
Because these molecules can replace water-water hydrogen bonds with more energetically favorable water-solute interactions.
Why do non polar biomolecules not dissolve readily in water?
They interfere with water-water interactions but are unable to form water-solute interactions. The non polar molecules cluster together in water.
Why does water have a higher melting point, boiling point, and heat of vaporization than most other solvents?
Because of the intramolecular forces between H2O molecules. These interactions are hydrogen-bonds that are strong.
H-O-H Bond angle
104.5, slightly less than the 109.5 because of the lone pair sterics
Hydrophilic Compounds
Hydrophilic compounds have charges or highly electronegative atoms, and are water-soluble
-C6H12O6 (glucose) has polar OH groups and an aldehyde group; these OH groups can H-bond with water
-PO43- (phospate ion) has negative charges on the oxygen atoms
-NaCl (a salt) exists as Na+ and Cl- ions in aqueous solution
Hydrophobic compounds
Hydrophobic compounds tend to have few polar groups, and are water-insoluble
– c18h34o2 (oleic acid, a fatty acid) has a long carbohydrate chain, with a COO- group at one end; this long hydrocarbon make the molecule insoluble overall
-CH4 (methane) is uncharges and has no electronegative atoms
– Vitamin D (C27H44O) is a steroid-derived fat-soluble vitamin. It has a large hydrophobic portion with only one polar OH group
Lipid Bylayer
There are approximately 5 × 106 lipid molecules in a 1 ?m × 1 ?m area of lipid bilayer, or about 109 lipid molecules in the plasma membrane of a small animal cell. All of the lipid molecules in cell membranes are amphipathic (or amphiphilic)—that is, they have a hydrophilic (“water-loving”) or polar end and a hydrophobic (“water-fearing”) or nonpolar end.

The most abundant membrane lipids are the phospholipids. These have a polar head group and two hydrophobic hydrocarbon tails.

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