The Biological Importance of Weak Interactions

Basic Chemistry Recap

• Atom Structure: Atoms have electrons in orbits; the outermost shell is called the valence shell with valence electrons.
• Octet Rule: Atoms prefer to have 8 electrons in the valence shell for stability.
  • Atoms not fulfilling the octet rule are reactive.
  • Example: Sodium (Na) and Chlorine (Cl) interaction.
• Stability and Reactivity: Unstable atoms react to become stable through the transfer of electrons, like in ionic bonds.

Weak Interactions in Biology

• Non-covalent Interactions: Weak but significant in large numbers due to their cumulative effect.
• Types of Weak Interactions
  1. Ionic Interactions
  2. Hydrogen Bonds
  3. Van der Waals Interactions
  4. Hydrophobic Interactions

Ionic Interactions

• Definition: Electrostatic interactions between charged particles.
  • Example: Interaction between Na and Cl.
• Behavior in Environments: Strongest in a vacuum, weaker in aqueous environments.
• Biological Example: Occurrence in amino acids like lysine (positive) and glutamate (negative).

Hydrogen Bonds

• Definition: Occur when hydrogen is covalently bound to an electronegative atom (FON).
• Electronegativity: Atoms that attract electrons strongly, e.g., O, N, S.
• Dipole Interaction: Partial charges due to electronegativity differences leading to hydrogen bonds.
• Biological Example: DNA base pairing (A-T with 2 H-bonds, C-G with 3 H-bonds).

Van der Waals Interactions

• Definition: Occur between two uncharged atoms within Van der Waals radius.
• Types of Dipoles:
  1. Dipole-Dipole Interactions
  2. Dipole-Induced Dipole Interactions
  3. Induced Dipole-Induced Dipole Interactions
• Biological Relevance: Important for protein folding and stability.

Hydrophobic Interactions

• Definition: Occur between nonpolar molecules in aqueous environments to minimize water interaction.
• Behavior: Nonpolar molecules aggregate to exclude water, minimizing surface area exposure.
• Biological Example: Protein 3D structure formation relies on hydrophobic interactions.

Next Topic

• Upcoming Video: Discussion on organic molecules in organisms and their functions.