Gluconeogenesis: Key Processes and Enzymes

Importance of gluconeogenesis between meals

To maintain blood glucose levels for the brain and red blood cells.

Organ performing gluconeogenesis

Liver

Energy molecules consumed in gluconeogenesis

6 ATP equivalents

Difficulty in reversing glycolysis

Three irreversible steps in glycolysis

Three irreversible enzymes in glycolysis

Hexokinase, PFK-1, Pyruvate kinase

Enzyme converting pyruvate to oxaloacetate

Pyruvate carboxylase

Function location of pyruvate carboxylase

Mitochondria

Enzyme converting oxaloacetate to PEP

PEP carboxykinase (PEPCK)

Function location of PEPCK

Cytoplasm

Cofactor needed by pyruvate carboxylase

Biotin

Reason fatty acids can't be used to make glucose

Humans lack enzymes to convert acetyl-CoA to pyruvate

Compound derived from fat that can enter gluconeogenesis

Glycerol

Enzyme hydrolyzing F-1,6-bisphosphate

Fructose-1,6-bisphosphatase

Location of glucose-6-phosphatase

Endoplasmic reticulum

Role of glucose-6-phosphatase

Converts G-6-P to glucose for release into blood

Cycle converting muscle lactate to liver glucose

Cori Cycle

Most important glucogenic amino acid

Alanine

Enzyme converting lactate to pyruvate

Lactate dehydrogenase (LDH)

Fate of NH₃ from amino acid catabolism

Converted to urea

Organ performing the urea cycle

Liver

Reason muscle can't export glucose

Lacks glucose-6-phosphatase

Shuttle transporting oxaloacetate to the cytoplasm

Malate or aspartate shuttle

Gluconeogenic entry points

Pyruvate, OAA, PEP, DHAP, Glyceraldehyde-3-phosphate

Other carbohydrates feeding into gluconeogenesis

Fructose, Galactose, Mannose

How alanine enters gluconeogenesis

Transamination to form pyruvate

Overall reaction for pyruvate to PEP

Pyruvate + CO₂ + ATP + GTP → PEP + CO₂

Pathways to distinguish from gluconeogenesis

Glycolysis, Glycogenolysis, Glycogenesis, Glucogenesis