Pentose Phosphate Pathway Overview

Pentose Phosphate Pathway

• The pentose phosphate pathway, also called the hexose monophosphate pathway or 6-phosphogluconate pathway, occurs in the cytosol of cells.
• The pathway involves two, irreversible oxidative reactions, followed by reversible sugar-phosphate interconversions.
• The pathway does not directly consume or produce ATP.

Specific Objectives

• Understand the function of the pentose shunt.
• Explain the effect of glucose 6-P dehydrogenase deficiency.

Overview of Pentose Phosphate Pathway

• The pathway provides the body with NADPH, a crucial biochemical reductant.
• It produces ribose-5-phosphate needed for nucleotide biosynthesis.
• It helps metabolize five-carbon sugars from the diet or carbohydrates in the body.

Irreversible Oxidative Reactions

• The production of ribulose 5-phosphate, CO2, and two molecules of NADPH occur for each molecule of glucose 6-phosphate oxidized.
• One glucose 6-phosphate oxidized results in two NADPH molecules.

Oxidative Stages of Pentose Phosphate Pathway

• Glucose-6-phosphate undergoes dehydrogenase to 6-phosphogluconolactone. This is followed by gluconolactonase that produces 6-phosphogluconate. 6-phosphogluconate undergoes dehydrogenase to produce ribulose-5-P.
• The reactions generate NADPH and CO2, and are crucial for reducing oxidative stress and providing NADPH for biosynthesis.

Site of Action

• The pentose pathway is vital in the liver, lactating mammary glands, and adipose tissue, which produce fatty acids, especially those dependent on NADPH.
• It's also key in the testes, ovaries, placenta, and adrenal cortex for steroid hormone synthesis, again dependent on NADPH.
• Red blood cells (RBCs) require NADPH to keep glutathione reduced.

Reversible Nonoxidative Reactions

• These reactions occur in all cells that synthesize nucleotides and nucleic acids.
• They allow ribulose-5-phosphate to yield ribose-5-phosphate, a component of nucleotide synthesis.
• They also generate intermediates of glycolysis (fructose 6-phosphate and glyceraldehyde 3-phosphate).

Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD)

• G6PD deficiency is an inherited condition causing hemolytic anemia.
• Erythrocytes are unable to detoxify oxidative agents due to inadequate NADPH production, leading to hemolysis.
• G6PD deficiency is X-linked, stemming from various gene mutations.

Clinical Manifestations of G6PD Deficiency

• Neonatal jaundice, potentially severe, frequently arises 1 to 4 days after birth due to increased production of unconjugated bilirubin.
• Chronic hemolysis can shorten the lifespan of individuals with severe G6PD deficiency.
• Female carriers of the deficient gene show increased resistance to malaria.

Explore the key functions and processes of the pentose phosphate pathway. This quiz delves into its role in NADPH production, nucleotide biosynthesis, and the implications of glucose 6-P dehydrogenase deficiency. Test your understanding of this essential metabolic pathway.