Biochemistry: Water and Reactions

Water and Hydrogen Bonds

• 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.

Oxidation/Reduction Reactions

• 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+.

Spontaneity of Life Processes and Free Energy

• 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 & Hydrophobic Substances

• 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 Substances

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

Soap's Amphipathic Molecules

• 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.

Phospholipid Bilayers

• Phospholipid bilayers are the basis of cell membranes.
• Phosphoglycerides are the main component of phospholipids.
• The tails of phospholipids are typically 16-18 carbons long.
• Phospholipid compositions vary, and bilayers are asymmetric.
• Phospholipid bilayers are self-sealing.

Liposomes

• 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.

Protein Folding Based On Hydrophobicity

• Protein folding is influenced by hydrophobicity.
• Hydrophobic amino acids tend to cluster together in the interior of proteins.
• This clustering helps reduce the contact of hydrophobic groups with water.
• Folding is a complex process driven by multiple interactions.

Bond Energies and Strength

• 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)