Gluconeogenesis Flashcards
What is gluconeogenesis?
The pathway that makes glucose
When does gluconeogenesis take place?
- Occurs when blood glucose is low.
- The hormone glucagon is involved in this process
What is used to make glucose during starvation, low/no carbohydraes, and exercise?
Starvation: primarily amino acids
Low/no carbohydrates: primarily amino acids
Exercise: lactic acid and alanine
What are the main non-carbohydrate precursors for gluconeogenesis?
Lactic acid, alpha-keto acids, and glycerol
How much glucose does the brain need?
100 grams per day (400 kcal)
Gluconeogenesis only occurs in special locations. What are they?
- Liver (90%)
- Kidneys (10%)
What are the enzymes responsible for the irreversible reactions of glycolysis?
- Hexokinase (glucokinase)
- Phosphofructokinase
- Pyruvate kinase
How is gluconeogenesis made favorable?
- Using alternative enzymes
- Couple the reactions to energy liberating reactions
- Use ATP or the equivalent
What is the first obstacle in that gluconeogenesis must overome to proceed?
Converting pyruvate into phosphoenolpyruvate
How is pyruvate converted to phosphoenolpyruvate in gluconeogenesis?
- Pyruvate is converted to oxaloacetate with pyruvate carboxylase and the coenzyme biotin
- Oxaloacetate is converted to phosphoenolpyruvate by PEP carboxykinase
What is the second obstacle in that gluconeogenesis must overcome to proceed?
Converting fructose 1,6-bisphosphate to fructose 6-phosphate
How is fructose 1,6-bisphosphate converted to fructose 6-phosphate in gluconeogenesis?
Fructose 1,6-bisphosphate is converted to fructose 6-phosphate by fructose 1,6- bisphosphatase
What is the third obstacle that gluconeogenesis must overcome to proceed?
Converting glucose 6-phosphate into glucose
How is glucose 6-phosphate converted into glucose in gluconeogenesis?
Glucose 6-phosphate is converted into glucose by glucose 6-phosphatase
This is the backbone of triglycerides. It is not a fat.
Glycerol
This is the “waste” product of glycolysis.
Lactic acid
These are derived from glycogenic amino acids. They can enter into TCA forming OAA, which is the direct precursor to PEP. It is the primary source of glucose from GNG at rest and during fasting.
Alpha-ketoacids
What is the Cori cycle?
It is the process by which muscles use glycogen during exercise for the Kreb’s cycle. It produces lactate, which is then taken up by the liver to make glucose, which is sent back into the bloodstream and then stored again in muscle glycogen.
What alpha ketoacid is alanine associated with?
Pyruvate
What alpha ketoacid is glutamate associated with?
Alpha-ketoglutarate
What alpha ketoacid is aspartate associated with?
Oxaloacetate
What amino acid is pyruvate associated with?
Alanine
What amino acid is alpha-ketoglutarate associated with?
Glutamate
What amino acid is oxaloacetate associated with?
Aspartate
What happens to an alpha keto acid depends on what four things?
- Energy charge
- Hormones (glucagon/insulin)
- Glucose concentration
- Tissue (liver vs muscle)
Describe what happens in the glucose-alanine cycle.
Starts in the muslce: Glycogen–>Glucose 6P–>Pyruvate–> Alanine–>Moves to liver–>Pyruvate and NH3+–>Glucose and Urea–> glucose is transported to muscle
When does the glucose-alanine cycle primarily occur?
During exercise
This hormone is secreted by beta cells of the pancreas, it lowers blood sugar, stimulates glycogen formation, and inhibits gluconeogenesis.
Insulin
This hormone is secreted by alpha cells of the pancreas, elevates blood sugar, stimulates glycogen breakdown, and stimulates gluconeogenesis.
Glucagon
How does fructose 2,6-bisphosphate influence glycolysis and gluconeogenesis?
- Stimulates glycolysis (stimulates PFK in the liver)
- Inhibits gluconeogenesis (inhibits fructose 1,6-bisphosphate)
What are some stimulators of glycolysis?
- Glucose
- Insulin
- AMP, ADP
- NAD+
- Fructose 2,6-bisphosphate
What are some inhibtors of glycolysis?
- ATP
- NADPH
- Glucagon
- Pyruvate
- Lactate
- Alanine
- Citrate
What are some stimulators of gluconeogenesis?
- Glucagon
- Acetyl CoA
- Citrate
What are some inhibitors of gluconeogenesis?
- Glucose
- Insulin
- AMP, ADP
