0415 - Lipid and carbohydrate anabolic pathways - EG Flashcards
What molecules are the major promotors of lipid synthesis?
Increased concentration of citrate, NADH and ATP, as represent high energy, therefore acetyl CoA is not required to enter the TCA cycle.
What is the first, committed step of fatty acid synthesis and how is it regulated?
The conversion of acetyl Co-A to malonyl Co-A by acetyl-CoA carboxylase, which effectively adds CO2. acetyl-CoA carboxylase is stimulated by citrate and insulin, inhibited by palmitoyl Co-A and glucagon and adrenalin.
Where does fatty acid synthesis occur and what are the major steps?
Cytosol. (1) transfer step to malonyl Co-A. (2) condensation (3) reduction (4) dehydration (5) reduction (6) re-setting
Where does the pentose phosphate pathway occur?
Cytosol
What is the purpose of the pentose-phosphate pathway?
To restore glutathione (GSH)levels, which are used as antioxidants. To provide energy for other anabolic reactions. To provide nucleotides. Can also shunt back into the glycolysis pathway.
What is the first step in the pentose phosphate pathway?
Glucose-6-P is converted to 6-phosphonogluconate by the enzyme G-6-P-DH. This step is linked to the conversion of NADP to NADPH which is able convert GSSG (oxidised) back into GSH (reduced) which is able to act as an antioxidant.
How much glucose does the brain use per day?
~120g/day
Where does glucose synthesis (gluconeogenesis) occur? Why in only these organs?
In the liver majorly and to some extent in the renal cortex, only these organs have G-6-Phosphatase to convert G-6-P back to glucose.
What is the overall equation in glucose synthesis?
2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 4 H20 => Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ + 2 H+
What is the three steps that overcome the committed steps of glycolysis to enable gluconeogenesis?
(1) The conversion of pyruvate back to oxaloacetate by PC and the conversion of OAA to PEP by phosphoenolpyruvatecarboxykinase (PEPCK).(2) F-1,6-BP converts F-1,6-PH to F-6-P. (3) G-6-Phosphatase converts G-6-P to glucose.
Which hormones inhibit and which stimulate gluconeogenesis?
Glucagon and adrenalin stimulate gluconeogenesis, insulin inhibits.
How does fructose 2,6-bisphosphate regulate glycolysis?
when F-2,6,BP concentration is high it activates PFK-1 to stimulate glycolysis, and inhibits FBPase-1 to inhibit gluconeogenesis (and reverse when concentration is low).
How is the cellular concentration of fructose 2,6-bisphosphate determined?
by a bifunctional protein, which when dephosphorylated (by insulin) becomes PFK-2 to convert G-6-P to F-2,6-BP (stimulate glycolysis/inhibit gluconeogenesis), and when phosphorylated (by glucagon) becomes FBPase-2 to convert F-2,6-BP back to F-6-P (stimulate gluconeogenesis/inhibit glycolysis).
