Lecture 3: Gluconeogenesis Flashcards
How long do glycogen stores last in a fasting state?
About a day
Where does gluconeogenesis occur?
In the liver
Discuss the energetics of gluconeogenesis.
Gluconeogenesis is a very energetically costly process: it uses up a lot of ATP (6 ATP equivalents for every glucose molecule synthesised: 4 ATP and 2 GTP)
When and why is gluconeogenesis essential?
Gluconeogenesis is essential when food intake is low, for producing glucose for the brain and red blood cells.
Give the overall equation for gluconeogenesis, indicating the number of each molecule.
2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 2H+ + 4H2O
—>
Glucose + 4 ADP + 2 GDP + 2 NAD+ + 6 Pi
Where does the pyruvate used in gluconeogenesis come from?
- Lactate
- Some amino acids (during starvation - from diet or breakdown of muscle)
- Glycerol (released form fats (triglycerides))
What is gluconeogenesis the opposite of substrate-wise? Name the substrates in order.
Glycolysis Substrates: Pyruvate Oxaloacetate Phosphoenolpyruvate (PEP) 2-Phosphoglycerate 3-Phosphoglycerate 1,3-Bisphosphoglycerate Glyceraldehyde-3-phosphate Dihydroxyacteone phosphate Fructose-1,6-bisphosphate Fructose-6-phosphate Glucose-6-phosphate Glucose
Which of the reactions in glycolysis are irreversible?
Glucose —> Glucose-6-phosphate
Fructose-6-phosphate –> Fructose-1,6-bisphosphate
Phosphoenolpruvate —> Pyruvate
Give the enzymes which catalyse gluconeogenesis, in order.
pyruvate carboxylase Phosphoenolpyruvate (PEP) carboxykinase enolase phosphoglycerate mutase phosphoglycerate kinase glyceraldehyde phosphate dehydrogenase triose phosphate isomerase (x2) aldolase fructose-1,-6-bisphosphatase phosphohexose isomerase glucose-6-phosphatase
Give the enzyme which catalyse glycolysis, in order.
hexokinase phosphohexose isomerase phosphofructokinase 1 aldolase triose phosphate isomerase glyceraldehyde phosphate dehydrogenase phosphoglycerate kinase phosphoglycerate mutase enolase pyruvate kinase
Which two reactions in gluconeogenesis are exergonic?
Pyruvate (+ bicarbonate) —> Oxaloacetate (uses GTP)
Oxaloacetate —> Phosphoenolpyruvate (uses ATP)
What is an anaplerotic reaction?
A ‘filling up’ reaction, which supplies a substrate to ‘fill up’ /keep going a metabolic pathway, usually the TCA cycle.
Give an example of an anaplerotic reaction in gluceoneogenesis.
Pyruvate + bicarbonate (+ATP) —> Oxaloacetate (+ADP +Pi)
Requires cofactor biotin (form vitamin b7) and enzyme pyruvate carboxylate
This is a carboxylation reaction too.
In the reaction converting Oxaloacetate to Phosphoenolpyruvate, what else is used/produced?
Used: GTP
Produced: GDP and CO2
Why is biotin required in the first step of gluconeogenesis?
Biotin can carry CO2. Pyruvate carboxylase, the enzyme which catalyses the first step of gluconeogenesis, is biotin-dependent. Biotin moves the CO2 from site 1 to site 2.