Question

This question is about the pentose phosphate pathway and interconnected metabolic pathways (glycolysis, gluconeogenesis.)

a) What reactions would occur if the cell needed lots of NADPH and only NADPH?

b) What reactions would occur if both NADPH and ATP were both needed?

c) What reactions would occur if nucleotides were needed for DNA synthesis and that was the primary need?

Answer 1

a) The pentose phosphate pathway meets the need of all organisms for a source of NADPH to use in reductive biosynthesis. This pathway consists of two phases: the oxidative generation of NADPH and the nonoxidative interconversion of sugars. In the oxidative phase, NADPH is generated when glucose 6-phosphate is oxidized to ribose 5-phosphate. Glucose 6-phosphate is oxidized to 6-phosphoglucono-?-lactone to generate one molecule of NADPH. The lactone product is hydrolyzed to 6-phosphogluconate, which is oxidatively decarboxylated to ribulose 5-phosphate with the generation of a second molecule of NADPH.

b) Glycolysis is the anerobic breakdown of the glucose into 2 pyruvate molecules. In the process, it produces 2 ATP molecules and 2 NADH molecules for the utilization by cell. The first phase of glycolysis requires energy, while the second phase completes the conversion to pyruvate and produces ATP and NADH for the cell to use for energy. Overall, the process of glycolysis produces a net gain of two pyruvate molecules, two ATP molecules, and two NADH molecules for the cell to use for energy.

c) Pentose phosphate pathway is utilized for the generation of ribose 5-phosphate. This five-carbon sugar and its derivatives are components of RNA and DNA, as well as ATP, NADH, FAD, and coenzyme A. In the nonoxidative phase, the pentose phosphate pathway catalyzes the interconversion of three-, four-, five-, six-, and seven-carbon sugars in a series of nonoxidative reactions that can result in the synthesis of five-carbon sugars for nucleotide biosynthesis.