Module 11 - Regulation of Citrate Cycle and Chemiosmotic Theory Flashcards
How did the relative concentrations of sucrose and citrate change over days of aspergillus fermentation?
started at 100% sucrose, shift to 100% citrate
What is an amphibolic pathway?
the citrate cycle is amphibolic because it functions in catabolic (oxidation of acetyl coA) and anabolic (production of precursors for fatty acid, amino acid, and heme biosynthesis) pathways
How is the flux of pyruvate entering the citrate cycle controlled?
pyruvate dehydrogenase is activated by CoA and stimulates acetyl CoA production
pyruvate carboxylase is stimulated by acetyl CoA to maintain oxaloacetate for citrate synthesis
This means that pyruvate carboxylase balances the input of oxaloacetate with acetyl CoA when stored fat is metabolized. If there is a lot of acetyl CoA, that means that there isn’t enough oxaloacetate to convert it, so PC is stimulated to make more.
When Aspergillus niger fermentation creates citrate, why does the natural citrate cycle NOT occur instead?
the culture condition inhibit part of the citrate cycle, and instead the citrate formed is exported out of the mitochondria
citrate lyase is inhibited (so it is not turned into acetyl CoA and oxaloacetate) and it continues to be exported out of the cell
What is an anaplerotic reaction?
reactions that replenish citrate cycle intermediates that have been shunted to other metabolic pathways
What metabolites of the citrate cycle are shared, and to what other processes?
acetyl coA: fatty acids and cholesterol
oxaloacetate: amino acids and glucose
a-ketoglutarate: amino acids
succinyl coA: heme
How does pyruvate carboxylate form oxaloacetate?
uses biotin to catalyze an ATP dependent reaction
PC binds carboxybiotin which is decarboxylated to release a CO2, a pyruvate enolate forms with the carboxybiotin, then the CO2 reacts with the pyruvate enolate to form oxaloacetate
How does pyruvate carboxylase function as an anaplerotic reaction?
phosphoenolpyruvate is…
- turned into oxloaetate by phosphoenolpyruvate carboxylase
OR - turned into malate by pyruvate kinase and malic enzyme
What is the chemiosmotic theory statement?
energy from redox reactions is translated into vectorial energy in the form of a proton gradient by coupling the electron transfer to membrane bound proton pumps
What are the two types of gradients in a proton circuit?
chemical gradient (delta pH)
membrane potential gradient (delta psi)
What is required for the chemiosmotic theory to work?
an enclosed mitochondrial membrane
In one sentence, how does the chemiosmotic theory work?
H+ are pumped. out of the matrix by the electron transport system and then flow back down the chemical and electrical gradients through an ATP-synthase complex
What do uncoupler proteins and inhibitors do to the proton circuits?
Uncoupler proteins direct energy away from ATP-synthesis and produce heat, while inhibitors stop proton flow and lead to cell death
The inner mitochondrial membrane is composed of…
80% protein, mostly ETC complexes and ATP synthase enzyme
Oxidative phosphorylation couples…
NADH oxidation with ATP synthesis