Pellagra results from a deficiency of nicotinamide, which is synthesized from tryptophan. Nicotinamide nucleotides are neither oxidized nor reduced during which step of cellular respiration.

a. glycolysis

b. chemiosmosis

c. citric acid cycle

d. electron transport chain

b. Chemiosmosis

Explanation:

Chemiosmosis refers to the process during which phosphorylation of ADP into ATP is driven by the energy of an electrochemical gradient. This electrochemical gradient was generated during the transfer of electrons down an electron transport chain. The components of the electron transport chain pump the protons across the membrane to produce a proton concentration gradient. During chemiosmosis, protons diffuse through the transmembrane channels of ATP synthase and ATP is synthesized. There is no reduction of NAD + or oxidation of NADH during chemiosmosis.