Lecture 7 Flashcards
Where does gluconeogenesis take place?
In the cytosol, mitochondrial matrix, and ER lumen
Where is pyruvate carboxylase found? In what reaction does it partake?
Only the matrix. Converts pyruvate into oxaloacetate (OAA).
What is the non-net reaction of glycolysis?
(2NAD+) + 4ADP + 4Pi + glucose -> 4ATP + 2pyruvate + 2NADH + 2ADP + 2Pi (I feel like there should be 2ATP in the reactants too?)
What is the net reaction of glycolysis?
Glucose + 2ADP +(2NAD+) + 2Pi -> 2pyruvate + 2ATP + 2NADH
Why does the non-net reaction of glycolysis use 4ADP, 4Pi, and produce 4ATP but the net reaction produces 2 of each?
In the non-net reaction, you need to input 2 ATP (1 to phosphorylate glucose and 1 so that PFK-1 can phosphorylate fructose 6-P). However, you also make 4ATP so need an input of 4ADP + 4Pi. The net reaction cancels out to 2ADP + 2Pi for inputs and 2ATP for output.
List the reactants/products for each step in glycolysis!
Glucose -> glucose 6-P -> fructose 6-P -> fructose 1,6-BP -> glyceraldehyde 3-P/DHAP -> 1,3-BPG -> 2,3-PG -> 2,2-PG -> PEP -> 2pyruvate
Where is PEPCK found?
Matrix and cytosol
Where is G6Pase found?
In the ER lumen
What is the reaction for the first bypass in gluconeogenesis? What step of glycolysis does it bypass?
2pyruvate + 2ATP -> OAA + 2GTP -> 2PEP
It bypasses step 10, where PEP gets converted to pyruvate. This time, pyruvate gets converted into PEP! Normally, PEP to pyruvate is very energetically favorable because pyruvate has a stable keto tautomer and PEP is unstable.
What are the two paths that convert pyruvate to PEP? Which enzymes are involved?
- PEP pathway (uses pyruvate carboxylase and PEP carboxykinase)
- Malate pathway (uses pyruvate carboxylase, mitochondrial/cytosolic malate DH, cytosolic PEP carboxykinase)
Explain the biotinyl-lysine tether involved in OAA formation
CO2 comes in the form of carbonate (HCO3-) and an input of ATP transfers a CO2 molecule over to the biotinyl tether’s site 1, forming a covalent bond. The tether is flexible such that it moves over to site 2 to drop off CO2 to pyruvate such that it becomes OAA.
Explain how pyruvate is converted to PEP in the malate pathway
Pyruvate is converted to OAA in matrix-> converts into aspartate -> transported from matrix to cytosol through glutamate-aspartate transporters -> converts again into OAA -> cytosolic PEPCK converts OAA to PEP.
Cycle continues where OAA in cytosol converts to malate through NADH oxidation -> malate transporter into matrix -> regenerate NADH -> make OAA -> repeat cycle
What is the second bypass in gluconeogenesis? Which step of glycolysis does it bypass? What is the key enzyme here?
ATP + H2O -> Pi + ADP + heat
It bypasses step 3 of glycolysis (PFK-1). Fructose 1,6-BP converts back to fructose 6-P. FBP-1 is key.
What is the third bypass of gluconeogenesis? Which step of glycolysis does it bypass? Which enzyme is key here?
2pyruvate + 2GTP + 4ATP +2NADH + (2H+) + 4H2O -> 1glucose + 2GDP + 4ADP + 6Pi + 2NAD+
Bypasses step 1 of glycolysis. Glucose 6-phosphatase dephosphorylates glucose 6-P to glucose, which moves back out into the blood when blood glucose is low
Why aren’t gluconeogenesis and glycolysis simply the reverse of each other?
Gluconeogenesis uses GTP and glycolysis does not.
The ATP numbers are not balanced: 2 for glycolysis and 4 for gluconeogenesis.
