Biochem Intermolecular Forces

• Hydrogen Bonding can occur between:

  1. hydroxyl group of an alcohol and water
  2. carbonyl group of a ketone and water
  3. peptide groups in polypeptides
  4. complementary bases of DNA
• Hydrophobic means that a substance cannot dissolve in water.
• Hydrophilic means a substance can dissolve in water.
• Proteins are constructed from 20 amino acids linked by peptides to form long, unbranched polymers.
• Functions of Proteins:

  1. signal molecules: polymers fold and facilitate biochemical functions
  2. receptors: convey to a cell that a signal has been received and initiates the cellular response
  3. structure: allows mobility and provides defense against danger
  4. catalysts: enhance the rate of a chemical reaction without being permanently affected themselves
• Polysaccharides and carbs are fuels and informational molecules. They are linked together in chains to help the cells recognize one another.
• Lipids form barriers that delineate the cell and cellular compartments.
• Lipids are an important storage form of energy because the hydrophobic components can undergo combustion to provide large amounts of cellular energy.
• Nucleic acids are information molecules of the cell because they contain instructions for cellular functions and interactions.
• The function of nucleic acids is to store and transfer information.
• Nucleic acids are constructed of 4 nucleotides, which are 5 carbon sugars attached to a base and at least one phosphoryl group.
• Hydrogen Bonding is an electrostatic force of attraction between a hydrogen atom covalently bonded to a more electronegative donor atom or group and another electronegative acceptor atom or group.
• Attraction is the force attracting atoms to one another and binding them together in a molecule.
• Repulsion is when two poles or charges push each other away.
• Hydrophobic interactions are a property of molecules that do not mix with water.
• van der Waals interactions are a weak attractive force between atoms or non polar molecules caused by a temporary change in dipole moment.
• cation + anion = ionic bonds
• London forces are a temporary attractive force that results when the electrons in two adjacent atoms occur positions that make the atoms form temporary dipoles.
• Dispersion of lipids in H20: each lipid molecule forces surrounding water molecules to spontaneously form ordered molecular aggregates where the hydrophilic ends are in contact with water, and the hydrophobic ends are shielded from the water.
• In clusters of lipid molecules, only lipid portions at the edge of the cluster force the ordering of water. Fewer water molecules are ordered, and entropy is increased.
• The Hydrophobic Effect is the energetic preference of non polar molecular surfaces to interact with other non polar molecular surfaces, displacing water molecules from the interacting surfaces.