Biochemistry: Water and Reactions

Study Notes

Water is highly polar due to the unequal sharing of electrons between oxygen and hydrogen atoms.
The difference in electronegativity creates partial negative and positive charges, making water a polar molecule.
This polarity influences water's solvent properties, allowing it to dissolve polar compounds and interact strongly with itself.
Hydrogen bonds form between polar groups and water molecules.
A hydrogen bond donor (partially positive hydrogen atom) interacts with a lone pair of electrons on a hydrogen bond acceptor (electronegative atom).
Hydrogen bonds are crucial for many biological molecules, such as nucleotides.

Reduction involves the gain of electrons.
Oxidation involves the loss of electrons.
An example of an oxidation-reduction reaction is the reaction of H3CHC=O with NADH + H+ to form H3CH2COH + NAD+.

Biochemical processes occur spontaneously based on the Gibbs free energy change (∆G).
∆G = ∆H - T∆S, where ∆H is the enthalpy change, T is the temperature, and ∆S is the entropy change.
If ∆G < 0, the reaction will occur spontaneously in the forward direction.
If ∆G > 0, the reaction will not occur spontaneously.
If ∆G = 0, the reaction is at equilibrium.

Hydrophilic (water-loving) compounds dissolve readily in water.
Hydrophobic (water-fearing) compounds separate from water.
Examples of hydrophilic compounds include ionic compounds, polar organic compounds, weak acids, and sugars.
Examples of hydrophobic compounds include nonpolar hydrocarbons and lipids.
Hydrophobic effects are crucial for life, contributing to the formation of folded proteins, nucleic acids, and membranes.

Amphipathic (both feeling) or amphiphilic (both loving) compounds have distinct polar (water-soluble) and non-polar portions.
An example is a fatty acid.

Soap molecules, being amphipathic, form micelles when in water.
Micelles are spherical clusters of amphipathic molecules where the hydrophobic parts cluster away from water and the hydrophilic parts face outward.
Soap micelles trap non-water-soluble oils and grime within their core.

Liposomes are artificial vesicles.
Water-soluble drugs can be enclosed in the core of a liposome, while fat-soluble drugs can be incorporated into the lipid bilayer.
Surface sugars on liposomes can prevent destruction by the immune system.
Liposomes can be engineered with targeting proteins to deliver drugs to specific cells.

Covalent bonds are strong and involve the sharing of electrons.
Examples include:
- C-H (413 kJ/mol)
- O-H (460 kJ/mol)
Noncovalent bonds are weaker and involve interactions between molecules.
Examples include:
- Hydrophobic interaction (4-12 kJ/mol)
- Hydrogen bond (20 kJ/mol)
- Ion-dipole interaction (20 kJ/mol)