Gluconeogenesis Flashcards
muscle gluconeogenesis
used ONLY to replenish muscle glycogen for contraction when needed
gluconeogenesis is most active in _
hepatocytes
gluconeogenesis uses _ as starting substrates
glycolysis and TCA intermediates from degradation of glucose and other sugars, amino acids, and fats
Cori cycle
lactate is transported to liver and made into glucose through gluconeogenesis and then exported back to peripheral tissues
Glc-Ala cycle
muscle shunts pyruvate (in the form of alanine) into the liver for gluconeogenesis and then the liver will transport the glucose back to the muscle
triacylglycerol degradation
degradation of TAGs produces glycerol which can enter gluconeogenesis after conversion to DHAP in the liver (glycerol kinase in the liver for conversion)
Why can’t even chain fatty acids be used to make glucose?
because when even chain fatty acids are degraded, they will form acetyl-CoA, which can not go through a reverse reaction to form pyruvate
odd chain fatty acids
degradation will form propionyl-CoA, which can be converted to succinyl-CoA for gluconeogenesis (succinyl-CoA can form oxaloacetate, a substrate in the process)
Which amino acids can not be used as substrates for gluconeogenesis?
leucine and lysine because they produce acetyl-CoA
irreversible gluconeogenesis steps
- pyruvate –> PEP
- fructose-1,6-bisphosphate –> fructose-6-phosphate
- glucose-6-phosphate –> glucose
pyruvate –> PEP
pyruvate –> oxalaoacetate (by pyruvate carboxylase) –> PEP (by PEP carboxy kinase)
pyruvate carboxylase requires _
ATP –> ADP
PEPCK requires _
GTP –> GDP
What is added to pyruvate to make OAA?
a CO2 from biotin
What happens to OAA to make PEP?
decarboxylation (removing previous CO2) and phosphorylation
pyruvate carboxylase reaction takes place in _
mitochondria; rest of reactions are in cytosol like glycolysis
How can OAA or PEP cross mitochondrial membrane after carboxy kinase reaction?
malate shuttle; will also now generate cytosolic NADH for bis-PG –> DHAP/GAP
How is OAA transferred into cytosol if lactate is used as substrate?
aspartate aminotransferase
alcohol consumption
can result in hypoglycemia because ethanol is oxidized by NAD+, producing NADH –> this excess NADH will then drive pyruvate –> lactate and OAA –> malate; no substrates available for gluconeogenesis
fructose-1,6-bp –> fructose-6-P
catalyzed by fructose bisphosphatase
glucose-6-P –> glucose
glucose-6-phosphatase
gluconeogenesis energy requirement
comes from fatty acid oxidation
allosteric regulation
needs of the cell
hormonal regulation
needs of the body
acetyl-CoA inhibits _
pyruvate dehydrogenase to prevent oxidation of pyruvate
acetyl-CoA activates _
pyruvate carboxylase for conversion of pyruvate to OAA for gluconeogenesis
gluconeogenesis is inhibited by _
AMP, ADP, F-2,6-BP
F-2,6-BP in gluconeogenesis
activity will be decreased by phosphorylation of the Bifunctional Enzyme and activity of FBPase-2
glucagon
promotes cAMP activity (will phosphorylate Bifunc E) which inhibits glycolysis and promotes gluconeogenesis
glucagon also activates _
lipases in adipose tissue for increased fatty acid oxidation to provide energy for gluconeogenesis and acetyl-CoA
insulin
stimulates F-2,6-BP synthesis to activate PFK-1 and promote glycolysis; suppresses gluconeogenesis
Metformin
decreases gluconeogenesis activity by decreasing ATP/AMP ratio to decrease expression of irreversible enzymes
