Pentose phosphate pathway
Pentose phosphate pathway (PPP) is a secondary pathway of glucose metabolism, primary being glycolysis. Glucose enters PPP as glucose 6-phosphate. It occurs in the cytosol of tissues active in fatty acid biosynthesis. Those tissues are liver, mammary and adrenal glands and adipose tissue. There are two phases in the pathway: oxidative and non-oxidative. There are four steps involved in oxidative phase, during which glucose-6 phosphate gets converted to ribose 5-phosphate. In the non-oxidative phase, transaldolase and transketolase enzymes catalyze the reversible reactions for the regeneration of glucose 6-phosphate.

Glyoxylate cycle
Glyoxylate cycle is a variant of TCA cycle and occurs in bacteria and glyoxysomes of plants. It bypasses decarboxylations of citric acid cycle and allows net synthesis of glucose from acetyl CoA.

Gluconeogenesis
Gluconeogenesis is a process of biosynthesis of glucose from simpler non carbohydrate precursors such as oxaloacetate or pyruvate. It is a universal pathway in animals, plants, microbes and fungi. It converts pyruvate to glucose (reverse of glycolysis). The irreversible steps of glycolysis are circumvented by four key enzymes of gluconeogenesis. They are pyruvate carboxylase, phosphoenol pyruvate carboxy kinase, fructose-1, 6-bisphosphatase and glucose-6-phosphatase.

Glycogen synthesis
Glycogen synthesis takes place in the liver and muscle. All the enzymes of glycogen synthesis are located in the cytosol. Activation of glucose takes place followed by the sequential addition of activated glucose units by glycogen synthase. A brancher enzyme creates alpha 1-6 linkage.

Starch synthesis
Starch is synthesized in the chloroplasts of plants with the help of enzymes ADP-glucose phosphorylase and starch synthase.

Disaccharide synthesis
Lactose is synthesized in lactating mammary glands of animals with the help of enzyme lactose synthase. Lactose is made up of galactose and glucose. Sucrose is synthesized in plants.

Pentose phosphate pathway (PPP) is a secondary pathway of glucose metabolism, primary being glycolysis. Glucose enters PPP as glucose 6-phosphate. It occurs in the cytosol of tissues active in fatty acid biosynthesis. Those tissues are liver, mammary and adrenal glands and adipose tissue. There are two phases in the pathway: oxidative and non-oxidative. Glyoxylate cycle is a variant of TCA cycle and occurs in bacteria and plants. Gluconeogenesis is a process of biosynthesis of glucose from simpler non carbohydrate precursors such as oxaloacetate or pyruvate. Glucose is stored in the body in the form of glycogen. Glycogen synthesis takes place in the liver and muscle. Starch and sucrose are synthesized in plants. Lactose is synthesized in lactating mammary glands of animals.

• Concept maps showing general metabolisms and carbohydrate metabolism with PPP and gluconeogenesis.
• Concept map for PPP.
• Individual reactions are explained.
• Concepts maps for oxidative and non oxidative phase overview.
• Glyoxylate cycle and precursors for gluconeogenesis are explained through concept maps.

Pentose phosphate pathway

• Place of occurrence
• Oxidative phase – Steps I to IV
• Action of transketolase
• Action of transaldolase
• Non oxidative phase overview

Glyoxylate cycle

• Facts
• Pathway

Gluconeogenesis

• Introduction
• Physiological need for glucose synthesis
• Relationship to glycolysis
• Summary of gluconeogenesis
• Precursors
• Cori’s cycle
• Regulation of glycolysis and gluconeogenesis

Glycogen synthesis

• Introduction
• Synthesis of glycogen
• Branch formation
• Regulation of glycogen metabolism
• Reciprocal regulation

Starch synthesis

• Introduction
• Synthesis of starch

Disaccharide synthesis

• Lactose synthesis
• Sucrose synthesis