Gluconeogenesis Quiz

Gluconeogenesis Overview

• Primarily occurs in the liver and kidneys.
• Main purpose is to synthesize glucose from non-carbohydrate precursors during periods of fasting or low carbohydrate intake.
• Particularly important during prolonged fasting, intense exercise, or when carbohydrate intake is insufficient.

Key Enzymatic Reactions

• Coenzyme involved in Reaction 1a is Biotin.
• Reaction 1b is catalyzed by Pyruvate carboxylase.
• Glycolytic intermediate that continues through reversible reactions is Dihydroxyacetone phosphate (DHAP).
• Reaction 9 is catalyzed by Fructose-1,6-bisphosphatase.
• Reaction 10 is catalyzed by Glucose-6-phosphatase.

Bypass Reactions

• Bypass reaction 3 serves to circumvent the irreversible phosphofructokinase step of glycolysis, allowing gluconeogenesis to proceed efficiently.

Lactate and the Cori Cycle

• A product of anaerobic glycolysis is lactate.
• In the liver, lactate is converted back into glucose through gluconeogenesis.
• The Cori cycle outlines the production and recycling of glucose and lactate between muscle and liver.
• The Cori cycle can occur in red blood cells, where lactate is produced and shipped to the liver.

Glucogenic Amino Acids

• Glucogenic amino acids can be converted into glucose precursors; examples include alanine, glutamine, and serine.
• Alanine is converted to pyruvate via transamination using the enzyme alanine transaminase (ALT).
• Coenzyme required for the transamination reaction is pyridoxal phosphate (PLP).

Shuttle Systems

• The alanine shuttle system utilizes the conversion of alanine to pyruvate and vice versa for transport of nitrogen.
• In the malate shuttle, oxaloacetate is converted to malate to facilitate its transport across the inner mitochondrial membrane, as oxaloacetate cannot cross it directly.
• In the lactate shuttle, lactate in the cytosol can also be converted back to pyruvate when needed.

Additional Conversion Reactions

• Lactate is converted to pyruvate by the enzyme lactate dehydrogenase.
• Glycerol can enter the gluconeogenesis pathway by being converted to dihydroxyacetone phosphate (DHAP).
• Elevated levels of pyruvate activate pyruvate carboxylase, converting pyruvate to oxaloacetate, while phosphoenolpyruvate carboxykinase (PEPCK) converts oxaloacetate to phosphoenolpyruvate (PEP).
• Oxaloacetate is converted to malate by malate dehydrogenase.