SUMMARY

• 2.1 Thermal Motions Power Biological Interactions

  Brownian motion, the random movement of fluids and gases, is powered by the background thermal noise. Brownian motion inside the cell supplies the energy for many of the interactions required for a functioning biochemical system.

• 2.2 Biochemical Interactions Take Place in an Aqueous Solution

  Most biochemical interactions take place in aqueous solutions. Water is a polar molecule, with the oxygen atom bearing a partial negative charge and the hydrogen atoms a partial positive charge. The charges on water molecules interact with opposite charges on other water molecules to form hydrogen bonds.

• 2.3 Weak Interactions Are Important Biochemical Properties

  There are three common types of weak interactions found in biochemical systems. Electrostatic interactions take place between ions having opposite charges. The strength of electrostatic interactions depends on the nature of the medium. The basis of the hydrogen bond is the unequal distribution of charge that results whenever a hydrogen atom is covalently bonded to an electronegative atom, such as oxygen or nitrogen. Hydrogen bonds in biomolecules are weakened in the presence of water because water readily forms hydrogen bonds. Fleeting electrostatic interactions, termed van der Waals interactions, take place when the transient asymmetry of charges on one nonpolar molecule induce complementary asymmetry in nearby nonpolar molecules.

• 2.4 Hydrophobic Molecules Cluster Together

  The Second Law of Thermodynamics states that the entropy of the universe is always increasing. This law is the basis of the hydrophobic effect: nonpolar molecules in aqueous solutions are driven together because of the resulting increase in entropy of water molecules. The hydrophobic effect is one of the most important energy considerations in biological systems, accounting for much of the structure of life, including membrane formation and the specific folding of proteins. Functional groups are groups of atoms found in many different biomolecules that confer specific chemical properties.

• 2.5 pH Is an Important Parameter of Biochemical Systems

  The pH of a solution is a measure of hydrogen ion concentration and is an important parameter in biochemical systems, both in vivo and in vitro. Buffers are acid–base conjugate pairs that resist changes in pH. Buffers are crucial in biological systems because changes in pH can have drastic effects on the structure of biomolecules and can even result in death.