MODULE 11: Chapter 10.5 Flashcards
What is the primary function of the citrate cycle?
The citrate cycle generates redox power by oxidizing acetyl-CoA to NADH and FADH2 and provides biosynthetic precursors for other pathways.
What defines the citrate cycle as an amphibolic pathway?
It functions in both catabolic (oxidation of acetyl-CoA) and anabolic (production of precursors for fatty acid, amino acid, and heme synthesis) pathways.
What are the five citrate cycle intermediates that serve as biosynthetic precursors?
- Citrate
- α-ketoglutarate
- Succinyl-CoA
- Malate
- Oxaloacetate
What happens to citrate when the citrate cycle is feedback inhibited by ATP and NADH?
Citrate is exported from the mitochondria to the cytosol.
What enzyme cleaves citrate in the cytosol and what are the products?
Citrate lyase cleaves citrate to release acetyl-CoA and oxaloacetate.
What is the role of acetyl-CoA in the cytosol?
Acetyl-CoA is used for fatty acid and cholesterol biosynthesis.
What metabolic pathway can oxaloacetate be converted into in the cytosol?
Oxaloacetate can be converted to phosphoenolpyruvate for gluconeogenesis.
Which amino acids are derived from oxaloacetate and α-ketoglutarate?
- Aspartate (from oxaloacetate)
- Glutamate (from α-ketoglutarate)
What essential component for heme biosynthesis does the citrate cycle provide?
δ-aminolevulinic acid, synthesized from succinyl-CoA and glycine.
What is the primary anaplerotic reaction in the citrate cycle?
The pyruvate carboxylase reaction converts pyruvate into oxaloacetate.
What two active sites does pyruvate carboxylase contain?
- Active site for carboxylating biotin
- Active site for carboxylating pyruvate to form oxaloacetate.
What is anaplerotic reaction?
A reaction that replenishes key intermediates that have been shunted to other metabolic pathways.
What conditions lead to the allosteric activation of pyruvate carboxylase?
Accumulation of acetyl-CoA in the mitochondrial matrix.
Which other two anaplerotic reactions are mentioned for the citrate cycle?
- Phosphoenolpyruvate carboxylase
- Malic enzyme
What substrate does phosphoenolpyruvate carboxylase use to generate oxaloacetate?
Phosphoenolpyruvate and bicarbonate.
What is the role of malic enzyme in both prokaryotic and eukaryotic cells?
It catalyzes the carboxylation of pyruvate to form malate.
Why is the pyruvate carboxylase reaction considered the primary anaplerotic reaction in humans?
It supplies oxaloacetate to the citrate cycle.
What is the significance of diffusion of citrate cycle intermediates across the inner mitochondrial membrane?
Diffusion is negligible.
Fill in the blank: The citrate cycle is considered an _______ pathway.
[amphibolic]
True or False: Phosphoenolpyruvate carboxylase is a primary anaplerotic reaction in humans.
False
What vitamin is a coenzyme for pyruvate carboxylase?
Biotin
How is biotin deficiency in humans typically characterized?
Rarely observed due to adequate levels in most foods.
