Gluconeogenesis Flashcards
What is the synthesis of glucose de novo from non carbohydrate precursors?
Gluconeogenesis
Where does gluconeogenesis occur?
Liver and kidney
When is gluconeogenesis particularly important?
During times of fasting
What is the bypass reaction 1a (1) of GNG?
Pyruvate to oxaloacetate
Enzyme- pyruvate carboxylase
Coenzyme-biotin (helps add CO2)
ATP—>ADP
What is bypass reaction 1b (2) in GNG?
Oxaloacetate to phosphoenolpyruvate
Enzyme: phosphoenolpyruvate carboxykinase
GTP—>GDP
Removed CO2 from oxaloacetate
What happens in reactions 3 to 8 of GNG?
Phosphoenolpyruvate is a glycolytic intermediate and can continue through the reversible reactions of glycolysis.
What do we reach at step 9 GNG?
Another irreversible reaction is reached. We reach fructose 1,6-bisphosphate
What is the GNG bypass reaction 3?
Fructose 1,6-bisphosphate to fructose 6-phosphate
Enzyme: Fructose 1,6-bisphosphatase hydrolyzes
No ATP generated,
What is bypass reaction 4 of GNG?
Glucose 6-phosphate to glucose
Enzyme: glucose-6 phosphatase hydrolyzes
No ATP generated
What are the GNG precursors?
Lactate, glycerol, glucogenic AA (alanine)
_____________,produced as a byproduct of anaerobic metabolism in muscles, can be converted into pyruvate and then used for gluconeogenesis
Lactate (Cori cycle)
Certain ____________can be converted into pyruvate or intermediates in the citric acid cycle and enter gluconeogenesis.
Amino acids, such as alanine and glutamine
____________released from triglycerides during fat breakdown (lipolysis), can be converted into dihydroxyacetone phosphate (DHAP), an intermediate in glycolysis and gluconeogenesis.
Glycerol
_________________is
a glycolytic intermediate and can continue through the
reversible reactions of glycolysis
Phosphoenolpyruvate (PEP)
In the absence of sufficient oxygen (as in intense exercise), pyruvate is converted into lactate in what cells? What is the cycle involving lactate?
Muscle cells, then the lactate continues to the liver. The Cori cycle
What does pyruvate being converted into lactate in muscle cells help produce?
NAD+, which allows glycolysis to continue anaerobically, and produce more ATP.
Where does glycerol from triacylglycerol catabolism enter GNG?
Step 7 after its conversion into dihydroxyacetone phosphate (DHAP)
Where do both glycolysis and gluconeogenesis take place?
In the cytoplasm of the liver cell
Which enzyme catalyzes the conversion of glycerol to DHAP?
glycerol kinase
Amino acids that can serve as a substrate for
gluconeogenesis are called _______________.
glucogenic amino acids
All amino acids except what 2 can be glucogenic?
Leucine and lysine
What are the 2 fates of these glucogenic AAs?
Either be converted directly into pyruvate or into a citric acid cycle
intermediate
Glucogenic amino acids that are particularly important are _____________ and ________________.
Alanine and glutamine
Alanine can be converted to _____________, using what enzyme? And what coenzyme is required?
Pyruvate
Enzyme: Alanine transaminase (ALT)
Co-enzyme: pyridoxal phosphate (PLP) (derived from B6)
Transamination reaction (transfer of an amino group)
Transamination involves transferring an _______
group from an amino acid to an alpha __________
amine, ketoacid
Where does gluconeogenesis begin?
The mitochondria
Alanine is converted to pyruvate inside the _____________
Mitochondria
Lactate is converted to pyruvate in the _______________. Pyruvate is immediately shuttled into the _______________
cytosol/mitochondra
__________________cannot cross the inner
mitochondrial membrane to get back into the cytosol
to feed into gluconeogenesis
oxaloacetate
The malate shuttle is used when the starting substrate is ______________.
Alanine (or any other glucogenic AA)
What is converted into malate in the malate shuttle?
Oxaloacetate
Once oxaloacetate is converted to malate, malate crosses the inner ____________ _____________. Then once in the ______________ malate is converted back into oxaloacetate. Oxaloacetate is then converted to ________________ and continues on to what pathway?
mitochondrial membrane/ cytosol / phosophoenolpyruvate (PEP)
gluconeogenesis
Lactate is converted to pyruvate in the ______________. Pyruvate enters the ______________ & is converted to ________________.
Oxaloacetate is converted to _________________ and is then shuttled out to continue with gluconeogenesis.
cytosol / mitochondria / oxaloacetate / phosphoenolpyruvate (PEP)
