9.7 The Pentose Phosphate Pathway

Question 1

Pentose phosphate pathway (PPP) [hexose monophosphate (HMP) shunt]

Answer 1

• occurs in the cytoplasm of all cells, where it serves two major functions: production of NADPH and serving as a source of ribose 5-phosphate for nucleotide synthesis.
• inhibited by its product, NADPH (used in biosynthesis, in the immune system, and to help prevent oxidative damage)
• activated by one of its
  reactants, NADP+

Question 2

What is the first part of the PPP and the final product?

Answer 2

• The first part of the PPP begins with glucose 6 phosphate, ends with ribulose 5-phosphate, and is irreversible
• This part produces NADPH and involves the important rate-limiting enzyme glucose-6-phosphate dehydrogenase
  (G6PD)

Question 3

Why is G6PD induced by insulin?

Answer 3

• because the abundance of sugar entering the cell under insulin stimulation will be shunted into both fuel utilization pathways (glycolysis and aerobic respiration),

Question 4

Functions of NADPH

Answer 4

• primarily acts as an electron donor in a number of biochemical reactions. It thus can be thought of as a potent reducing agent
  because it helps other molecules be reduced
• NAD+ acts as a high-energy electron acceptor from a
  number of biochemical reactions. It thus can be thought of as a potent oxidizing agent because it helps another molecule be oxidized (and thus is reduced itself during the process). The NADH produced from this reduction of NAD+ can then feed into the electron transport chain to indirectly produce ATP
• Biosynthesis, mainly of fatty acids and cholesterol
• Assisting in cellular bleach production in certain white blood cells, thereby contributing to bactericidal activity
• Maintenance of a supply of reduced glutathione to protect against reactive oxygen species (acting as the body’s natural antioxidant)

Question 5

Glutathione

Answer 5

• a reducing agent that can help reverse radical formation before damage is done to the cell.