Chemical Properties of Biological Molecules

Facts

• W & C did not suggested the structure of DNA molecule, but they did not prove that double helices would form spontaneously outside the biological system. However, if you keep a set of two single helices at 1mM concentration, 25 degree C, 99% would form a double helix
• Resonance structure: A same molecule can be written in two different ways based on the bonding possibilities (alternative arrangements)
• Covalent Bonds : Sharing of more than 1 electron between the atoms - Stronger
• Types of Non-covalent bonds
  • Electrostatic interactions
  • Hydrogen bonds
  • Van der Waals interactions:
  • Hydrophobic interactions
• Laws of thermodynamics
  • Zeroth law of thermodynamics: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law helps define the notion of temperature.
  • First law of thermodynamics: When energy passes, as Work (thermodynamics)|work, as heat, or with matter, into or out from a system, the system's internal energy changes in accord with the law of conservation of energy. Equivalently, perpetual motion machines of the first kind are impossible.
  • Second law of thermodynamics: In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind are impossible.
  • Third law of thermodynamics: The entropy of a system approaches a constant value as the temperature approaches absolute zero. With the exception of non-crystalline solids (glasses) the entropy of a system at absolute zero is typically close to zero, and is equal to the natural logarithm of the product of the quantum ground states.