Unit 1: Biochemistry - #1 Water Reactions, Properties of Water

Dehydration Synthesis Reaction (Condensation)

• Assembly of macromolecules 

• Removal of an -OH from one reactant and -H from another reactant 

• The -OH and -H form H2O, while the two reactants join together forming a covalent bond 

• Type of Anabolic Reaction: Used to assemble small molecules together into larger ones 

Hydrolysis Reaction

• Reverse of dehydration reactions 

• Disassembly of macromolecules 

• Water is a reactant to split a large molecule into smaller subunits 

• A covalent bond in the reactant molecule is broken and the -H and -OH from the water are attached, forming two products 

Catabolic Reaction

Macromolecules broken down into subunits (eg. digestion)

Properties of Water

• Universal solvent

• Hydrogen bonds form between water molecules, forming a water lattice.

• This gives water the ability to float

Liquid Water

• Hydrogen bonds that hold the lattice together, constantly breaking and reforming in new configurations. 

• This gives liquid water its ability to float.

Ice

• Water lattice is a rigid crystalline structure 

• Each water molecule in ice forms four hydrogen bonds with neighboring water molecules 

• This spaces water molecules farther apart that in liquid, so ice is less dense

Specific Heat Capacity

• Specific heat: Amount of thermal energy required to increase the temperature of a given quantity of water by a degree. 

• As heat is added to water, most is absorbed by the process of breaking the H-bonds in the water lattice, which increases water temperature slowly 

• Water stays liquid until 100 degree C

Cohesion (Water Sticks to Water)

• A property of water where H-bond lattice results in water molecules staying close together 

• This creates surface tension: how difficult it is to stretch or break the surface of a liquid 

• This allows small insects to walk on water

Adhesion (Water Sticks to Other Stuff) 

• Property where water molecules can form H-bonds with other polar molecules

• Eg. Water sticking to your skin when you get out of the shower

Aqueous Solutions

• Water molecules are small and very polar 

• They surround other polar and charged molecules and ions 

• This hydration shell, reduces attraction between these other molecules and promote their separation (breaks the ion apart) 

• This separation allow the substance to dissolve in the solution

Hydrophilic Molecules

Polar molecules or ions that are strongly attracted to and very soluble in water

Hydrophobic Molecules

Non-polar molecules that are not strongly attracted to and soluble in water