Citric acid cycle Flashcards
What is the purpose of aerobic catabolism?
To capture energy in biological fuel molecules and use it to make ATP.
What is the function of the citric acid cycle?
To oxidize acetyl-CoA to CO2, generate high-energy products like NADH, FADH2/QH2, and GTP (NTP)
NTP= Nucleoside triphosphates
QH2=ubiquinol
Where does the citric acid cycle occur?
In the mitochondrial matrix (eukaryotes).
Is the citric acid cycle aerobic or anaerobic?
Aerobic. Oxygen is needed to reoxidize NADH and FADH2.
What is the term for a metabolic pathway that can be used for both catabolic and anabolic processes?
Amphibolic. The citric acid cycle is an example of an amphibolic pathway
What are some examples of molecules that can be metabolized to generate acetyl-CoA for the citric acid cycle?
Carbohydrates, fats, and proteins.
What is the first step in the citric acid cycle?
Acetyl-CoA (2C) combines with oxaloacetate (4C) to make citrate (6C).
What enzyme catalyzes the first step of the citric acid cycle and is it regulated?
Citrate synthase. This reaction is not regulated.
What happens to the citrate molecule in the citric acid cycle?
It undergoes a series of reactions, including two oxidative decarboxylations, ultimately leading to the regeneration of oxaloacetate.
How many NADH molecules are generated per acetyl-CoA in the citric acid cycle?
3 NADH molecules.
How many FADH2/QH2 molecules are generated per acetyl-CoA in the citric acid cycle?
1 FADH2/QH2 molecule
How many GTP molecules are generated per acetyl-CoA in the citric acid
1 GTP molecule.
Which steps in the citric acid cycle are oxidative decarboxylations?
The steps catalyzed by isocitrate dehydrogenase (step 3) and α-ketoglutarate dehydrogenase (step 4)
What is significant about the enzyme α-ketoglutarate dehydrogenase?
It catalyzes an oxidative decarboxylation step in the citric acid cycle that is similar to the pyruvate dehydrogenase (PDH) reaction. It is also regulated.
Which step in the citric acid cycle involves substrate-level phosphorylation?
The step catalyzed by succinyl-CoA synthetase (step 7) where GTP is generated.
Which enzyme in the citric acid cycle is FAD-dependent?
Succinate dehydrogenase, which is also an integral membrane protein and part of Complex II in the electron transport chain.
What happens to the FADH2 generated by succinate dehydrogenase?
It is reoxidized by donating electrons to coenzyme Q (ubiquinone), which is then reduced to ubiquinol (QH2).
How is the citric acid cycle regulated?
By the NAD+/NADH ratio and the concentrations of intermediates. Regulated enzymes include isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.
What molecules inhibit isocitrate dehydrogenase and α-ketoglutarate dehydrogenase?
NADH and ATP
What molecules activate isocitrate dehydrogenase and α-ketoglutarate dehydrogenase?
ADP and Ca++
Why is the citric acid cycle considered amphibolic?
Because its intermediates can be used in the synthesis of other molecules like amino acids, carbohydrates, fats, and nucleotides.
What are anaplerotic reactions?
Reactions that replenish citric acid cycle intermediates that may be consumed in other processes.
What is an important anaplerotic reaction and what enzyme catalyzes it?
he formation of oxaloacetate from pyruvate, catalyzed by pyruvate carboxylase
What molecules activate and inhibit pyruvate carboxylase?
Acetyl-CoA activates it, while ADP inhibits it.
What is the approximate ATP yield from the complete oxidation of one glucose molecule under aerobic conditions?
~ 32 ATP
How much ATP does anaerobic glycolysis generate?
2 ATP (net)
Why does the addition of oxygen to an anaerobic culture of yeast decrease glucose consumption?
Yeast cells can produce more ATP from glucose under aerobic conditions via the citric acid cycle and oxidative phosphorylation than through anaerobic fermentation.
Can lactate be used as a metabolic fuel in aerobic metabolism?
Yes, lactate can be oxidized to pyruvate, which then enters the citric acid cycle.
What are the energy capture steps in the citric acid cycle?
Steps 3, 4, 5, 6, and 8 generate NADH, FADH2, or GTP.
What are the oxidation reactions in the citric acid cycle?
Steps 3, 4, 6, and 8 involve oxidation.
Which reaction links glycolysis to the citric acid cycle?
The reaction catalyzed by the pyruvate dehydrogenase complex (Step 9).
What are the regulated steps in the citric acid cycle?
Steps 1, 3, 4, and 9 are regulated.
What is the substrate level phosphorylation step in the citric acid cycle?
Step 5, where GTP is generated.
