1.1 Structure of Water and Hydrogen Bonding

Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function. The subcomponents of biological molecules and their sequence determine the properties of that molecule. Living systems depend on properties of water that result from its polarity and hydrogen bonding. The hydrogen bonds between water molecules result in cohesion, adhesion, and surface tension.

water as a highly polar molecule

oxygen is overall negative, hydrogen is overall positive, results in unevenly distributed charge

hydrogen bonds

weak attraction between water molecules due to water’s polar nature

cohesion

molecules of water are attracted to each other due to hydrogen bonds

surface tension

the cohesive force at the surface of a liquid that allows it to resist external forces

adhesion

attraction between water and other polar molecules, allowing them to stick to other surfaces

capillary action

upward motion against gravity dependent on the attraction of water molecules to themselves (cohesion) and the surface (adhesion)

high specific heat

larger amount of energy (heat) needed to raise the temperature of 1 gram of a substance by 1 degree Celsius

• moderation of nearby climate and stabilization of marine ecosystems

• high heat of vaporization and evaporative cooling

evaporative cooling

process where the surface of an object becomes cooler during evaporation

effect of freezing on hydrogen bonds

hydrogen bonds expand when frozen, in solid form molecules stay in a crystalline structure

• ice floats

• insulation of liquid water below ice

universal solvent

water dissolves all polar and ionic substances (hydrophilic), like dissolves like

pH scale

• measures acidity/alkalinity, 0 as most acidic, 14 as most basic

• logarithmic, not linear, pH = -log[H+], pH difference of 1 implies a tenfold change in H+ concentration

• regulated in biological systems by buffers

buffer

solutions that resist changes in pH by absorbing or donating ions when needed, key to maintaining stable H+ concentrations in biological systems (homeostasis)

carbonic acid-bicarbonate buffer as the most important buffer in human blood

H⁺ + HCO₃⁻ ↔ H₂CO₃

• carbonic acid (H₂CO₃) donates H+ ions

• bicarbonate ion (HCO₃⁻) accepts H+ ions

• neutrality is crucial for life (homeostasis)