Biochemistry: Role of Water

Study Notes

Water is crucial for biological processes, comprising 70-85% of cell weight.
It's present in bodily fluids like blood, urine, and saliva.
Water acts as the solvent for biochemical reactions, facilitating transportation, temperature maintenance, waste removal, and digestive fluid production.

A water molecule consists of two hydrogen atoms bound to an oxygen atom via polar covalent bonds.
Polar covalent bonds occur when electron sharing is unequal due to differences in electronegativity between atoms.
This uneven distribution makes water a polar molecule.

Water's polarity enables it to readily dissolve ionic and polar compounds through:
- Ion-dipole interaction: Attraction between charged ions and the polar water molecules.
- Dipole-dipole interaction: Attraction between polar molecules.
Water cannot dissolve nonpolar molecules (like oils) due to the lack of dipoles.
- Hydrophobic: Nonpolar molecules that don't dissolve in water.
- Hydrophilic: Molecules that readily dissolve in water.
Amphipathic molecules: Possess both polar (hydrophilic) and nonpolar (hydrophobic) regions. Examples include long-chain fatty acids.

Micelle: A spherical arrangement of organic molecules in water solutions where hydrophobic tails cluster inward, and hydrophilic heads face the water.

A special case of dipole-dipole interaction where hydrogen, covalently bound to a highly electronegative atom (oxygen or nitrogen), interacts with the electron pair of another electronegative atom (usually oxygen or nitrogen).
Essential for stabilizing the 3D structures of biological molecules like DNA, RNA, and proteins.

Ionization of water: Water molecules transfer protons (H+) to form hydronium ions (H3O+) and hydroxide ions (OH-).
This process is reversible.
The equilibrium constant (Keq) describes the extent of ionization.