BiochemistryLesson 2 of 2 in the course Mitochondria and cellular respiration

Citric Acid Cycle: Reactions, Regulation, and Metabolic Roles

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

The citric acid cycle is a central pathway for extracting energy from nutrients and supplying molecules used in other cellular processes. This lesson introduces its purpose, location, names, and discovery.

The citric acid cycle is also called the Krebs cycle or the tricarboxylic acid (TCA) cycle. It oxidizes the two-carbon acetyl group of acetyl-CoA through a sequence of reactions. The energy released is captured in energy-rich molecules, especially NADH and FADH₂, and in one molecule of GTP or ATP per turn. NADH and FADH₂ can then supply electrons to oxidative phosphorylation, which produces most of the ATP associated with cellular respiration.

All flashcards

What is the citric acid cycle?
A series of enzyme-catalyzed reactions that oxidizes acetyl-CoA, captures energy, and regenerates oxaloacetate.
What makes the citric acid cycle amphibolic?
It supports both catabolic energy release and anabolic biosynthesis.
What is an anaplerotic reaction?
A reaction that replenishes intermediates in the citric acid cycle.
What is the role of succinate dehydrogenase?
It oxidizes succinate, transfers electrons to ubiquinone, and links the cycle to electron transport.
Which citric acid cycle intermediate can provide the carbon skeleton for glutamate?
α-Ketoglutarate.

Quiz questions

  1. What are the products of one turn of the citric acid cycle per acetyl-CoA?Answer: 3 NADH, 1 FADH₂, 1 GTP or ATP, and 2 CO₂
  2. During the first turn of the citric acid cycle, the carbon atoms released as CO₂ come from which source?Answer: Oxaloacetate already present in the cycle
  3. In the succinate oxidation step, where are electrons transferred after they reduce FAD?Answer: To ubiquinone, forming ubiquinol
  4. Which enzymes are activated by calcium to increase citric acid cycle flux?Answer: Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase
  5. Why do estimates of ATP yield from glucose oxidation vary?Answer: Shuttle costs, proton leakage, and oxidative phosphorylation inefficiencies vary

Based on the Wikipedia article Citric acid cycle, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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