# Suggested Homework Set 4

J.P. Allen, BioPhysical Chemistry, Wiley-Blackwell, 2008. (free PDF version for ASU students)

Chapter 6: problems 2, 8, 12, 15 & 16.

4-1: Nicotine adenine dinucleotide (NAD) is a cellular redox molecule that is involved in redox biochemistry throughout the respiratory system.  The reduced form of NAD is designated NADH and the oxidized form is designated NAD+.  An electrochemical cell is constructed using the half-cell for which the reduction reaction is given by

which is combined with the half-cells:

(A)

(B)

Write the overall reaction for the cells in the direction of spontaneous change.  Is the NAD reduced or oxidized in the spontaneous reactions (for A and B)?

4-2A: For the oxidation of acetaldehyde to acetate by Fe3+ present in the heme group of cytochrome-c, the cell potential is 0.835 Volts at pH = 7.  Calculate the equilibrium constant.

4-3: Calculate the (A) standard Gibbs free energy change and the (B) equilibrium constant for the oxidation of the formate ion to carbon dioxide at room temperature and pH = 7.

4-4A: The molal (m) concentrations of the principal ions in a sample of intracellular fluid are 0.15 m for potassium ions, 0.01 m for sodium ions, 0.04 m for magnesium ions, and 0.12 m for hydrogen phosphate ions.  Calculate the ionic strength of the intracellular fluid.

4-5A: The ‘phosphate transfer potential’ is simply the negative of the Gibbs free energy of hydrolysis in units of kilojoules. The phosphate transfer potential of the phosphorylated amino acid phosphoarginine is 33.2.  Calculate the Gibbs free energy change for the phosphorylation of arginine by ATP:

arginine + ATP  →   phosphoarginine + ADP