LEHNINGER PRINCIPLES OF BIOCHEMISTRY David L. Nelson and Michael M. Cox LEHNINGER PRINCIPLES OF BIOCHEMISTRY Sixth Edition CHAPTER 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway © 2013 W. H. Freeman and Company

The two phases of glycolysis

Breakdown of intracellular glycogen by glycogen phosphorylase

Metabolism of fructose for entry into glycolysis

Metabolism of galactose for entry into glycolysis Galactose is phosphorylated at carbon-1 by galactokinase to produce galactose 1-phosphate. Galactose is a C-4 epimer of glucose. Galactose 1-phosphate is converted to glucose 1-phosphate through a UDP nucleotide derivative and the enzyme UDP-glucose 4-epimerase.

Metabolism of mannose for entry into glycolysis

Under aerobic conditions NADH transfers its electrons eventually to oxygen, regenerating NAD+. Under anaerobic conditions pyruvate is reduced to lactate to regenerate NAD+ for glycolysis to continue.

Yeast contain the enzyme pyruvate decarboxylase that decarboxylates pyruvate to form acetaldehyde. Acetaldehyde is then reduced to ethanol under anaerobic conditions.

The human brain consumes over 120 grams of glucose each day Gluconeogenesis Glucose is made in the liver and transported to the brain in the blood stream. The human brain consumes over 120 grams of glucose each day

Alternative paths from pyruvate to phosphoenolpyruvate

General scheme of the pentose phosphate pathway

NADPH in high concentrations feedback inhibits the pentose phosphate pathway