Which of the following is a characteristic of chemical bonds? Shorter bonds are generally stronger than longer bonds. Covalent bonds often fall apart at physiological temperatures. The number of van der Waals bonds an atom can form is limited by the valence of that atom. Ordered groups of weak bonds are easily broken.

Which of the following is a characteristic of a hydrogen bond? Hydrogen bond donor atoms are usually nitrogen or oxygen. Like van der Waals bonds, hydrogen bonds are non-directional. The biologically most important hydrogen bonds involve hydrogen atoms covalently bonded to oxygen or nitrogen atoms. Hydrogen bonds are weaker than van der Waals bonds. 2

Weak bonds generally have energies between 1-7 kcal/mol. Which of the following statements does NOT accurately describe a characteristic or function of weak chemical bonds? Weak bonds generally have energies between 1-7 kcal/mol. Weak bonds do not require complementary molecular surfaces to be maximally effective. Weak bonds attach enzymes to substrates. Weak bonds mediate most protein-DNA and protein-protein interactions. 3

Water molecules are unable to form hydrogen bonds with each other. Which of the following concerning the chemical characteristic of water is true? Water molecules are unable to form hydrogen bonds with each other. Water molecules have a strong tendency to exclude polar groups. A frozen water molecule hydrogen bonded to three nearest neighbors represents the most favorable arrangement of molecules. Organic molecules that form hydrogen bonds tend to be soluble in water. 4

Which of the following statements concerning the energetics of covalent bonds is FALSE? Low activation energies are barriers that prevent spontaneous rearrangements of covalent bonds in cellular systems. A molecule linked together by weak covalent bonds has a larger amount of free energy than a molecule linked together by strong covalent bonds. A chemical reaction in which molecules are transformed into other molecules with less free energy generally proceeds slowly at physiological temperatures in the absence of a catalyst. Enzymes speed up chemical reactions by lowering the activation energies needed to break old covalent bonds during molecular rearrangements. 5

Coupled chemical reactions are required to activate various biological “precursor” molecules. (Activated precursors store free energy that can be used later in biosynthetic reactions such as DNA or protein synthesis.) Which of the following terms describes this class of coupled chemical reactions? oxidation hydrolysis group-transfer reduction 6

Which of the following supplies the necessary free energy to help drive DNA synthesis? release of a triphosphate group from a deoxynucleoside triphosphate molecule release of a single phosphate group from a deoxynucleoside triphosphate molecule release and subsequent splitting of two phosphate groups from a deoxynucleoside triphosphate molecule release of a single phosphate group from a deoxynucleoside diphosphate molecule 7