6. Glycolysis and Gluconeogenesis Flashcards
Where does NAD regeneration take place when conditions are anaerobic?
Mitochondria
NAD cannot pass the MM usually; how has it evolved to move between the MM and cytosol?
Glycerinophosphate shuttle
Malate-Aspartate shuttle
Explain the GP shuttle
NAD maintains glycolysis in cytosol
Dihydroxyacetonphosphate forms glycerin-3-phosphate
G-3-P enters mitochondria
G-3P reforms Dihydroxyacetonphosphate
Coenzyme FAD is reduced in this reaction
Dihydroxyacetonphosphate returns to cytosol
Explain the M-A shuttle
OAA -> Malate Malate into mitochondria Malat -> OAA NAD reduced OAA -> Aspartate Aspartate back into cytosol Aspartate -> OAA
Explain NAD regeneration in anaerobic conditions
Reduced NAD during glycolysis formed when glyceraldehyde-3-phosphate -> 1,3-biphosphoglycerate
NAD reformed when pyruvate -> lactate
What is the fate of lactate?
Reforms pyruvate when oxygen becomes plentiful again
Forms glucose via gluconeogenesis in muscles
How long can the body survive without food?
30-40 days
Why is gluconeogensis important for erythrocytes and the brain?
Both have absolute glucose requirements
What level must BG be maintained at?
4-8mM
What is gluconeogenesis?
Formation of glucose from non-carbohydrates
Occurs in the liver, mainly
What is glycolysis?
Energy capture in the form of ATP and NADH from conversion of glucose into pyruvate
Substrates for gluconeogenesis
Pyruvate Lactate Amino Acids (only leucine and lysine are non-gluconeogenic) Glycerol OAA
Explain gluconeogenesis from fatty acids
Cannot occur from FFA
Explain gluconeogenesis from triglycerides
TG -> 3FFA + Glycerol
Glycerol -> Glyceraldehyde-3-phosphate -> fructose-1,6-bisphosphate
Explain the relationship between glycolysis and gluconeogenesis
Gluconeogensis is glycolysis in reverse apart from the three irreversible steps
How much ATP does gluconeogenesis require?
6
Where are the ATP for gluconeogenesis obtained from?
Pyruvate carboxylase
PEP carboxykinase
Phosphoglycerate kinase
How many NADH molecules does glyceraldehyde DH consume?
2
Relationship between AMP and ATP
At high energy levels: ATP high, AMP low
When does AMP stimulate glycolysis produce ATP?
Low energy levels
What does AMP inhibit and why?
Gluconeogenesis; to prevent futile cycles and conserve energy
How is glycolysis inhibited?
ATP at high energy levels
What intermediates stimulate gluconeogenesis?
Citrate and Acetyl CoA
Fructose-2,6-Bisphosphate is a regulatory molecule. How is it synthesised and subsequently broken down?
Synthesised by PFK2 from F-6-P
Broken down by FBPase2
