Water/Intro

Proteins functions

Enzymes, signal transduction, structural

Lipid functions

Structural, energy storage, hormones

Carb functions

Energy storage, cell signaling, structural

Nucleic acid function

Storage of genetic info, structural, energy storage, energy metabolism

Functional group polar bond examples (5)

• C-O, carboxyl/carbonyl

• H-O, alcohol

• H-N, amino

• H-S, Thiol/sulfhydryl

• P-O, phosphate/phosphoryl

Water overview

• 4 Hbonds/molecule in Ice

• 3.4 Hbonds/molecule in water

• Hydrogen bonds are weak interactions (not bonds), but there are so many of them that they are stronger together (1 velcro vs 500 velcro)

• Hydrogen bonds are strongest when linear (optimal electrostatic attraction is attained)

Why does water melt so easily?

Although enthalpy must be positive- (energy is needed) to melt ice, melting promotes an increase in entropy which is favoured in this reaction (resulting in negative gibbs energy, thus it is spontaneous)

• Melting is an entropy driven process

Electrostatic attraction

Attraction between oppositely charged ions (why ions easily dissolve in water)

1. Break NaCl bond (endothermic)

2. Break hydrogen water bond (endothermic)

3. Form water-ion interactions (exothermic)

4. The net enthalpy change is therefore small, and as solid NaCl is highly ordered, NaCl in solution is disordered, increasing entropy. (Entropy increases with solvation)

Van der waals interactions

A short range, very weak attraction (dispersion) due to induced temporary dipoles.

• Nonpolar hydrocarbons interact with these typically

Hydrophobic effect

The tendency of nonpolar molecules (or part of molecules) to cluster together in water. Entropy increases when nonpolar molecules come together.

1. Water forms a cage around nonpolar molecule, decreasing entropy

2. Water forms a larger cage around two nonpolar molecules as they come together into a larger mass, increasing entropy

(at dissolvement, entropy decreases, but as nonpolar molecules aggregate, entropy increases)

• The cage formed by water molecules favours van der waal interactions between H2O and nonpolar molecule, as well as H2O-H2O hydrogen bonding

• Non-polar molecules interfere with the hydrogen bonding in water (why dissolvement is unfavourable)

Ranking solubility

• Zwitterions are less soluble than charged molecules, as zwitterions are neutral and can’t form electrostatic interactions

• The larger the size of the molecule, the less soluble it is

What is the most stable macromolecule confirmation

Those in which hydrogen bonding is maximized within the molecule and between the molecule and the solvent, and in which hydrophobic components cluster in the interior of the molecule away from the aqueous solvent (micelle is formed)

• Weak, non-covalent interactions, in large numbers influence the folding of macromolecules