What can be said about this structure: a. This is the general arrangement for an amino acid. b. The structure is a "zwitterion. c. This molecule would always be present at a very low pH. d. This would easily move in a gel subject to an electrical field. e. Both A & B are correct What happens to NAD during catabolism reactions? a. It is hydrolyzed b. It is reduced c. It is oxidized d. It is excreted via feces e It is fed to chickens The receptors on the surfaces of cell membranes are very likely a. lipids. b carbohydrates. c proteins. d. nucleic acids. e. steroids. Polar (R) side groups on amino acids are said to be ____ because molecules. a. hydrophilic b. hydrophobic c. always ionized d. unreactive e. none of these