L24 - Krebs Cycle

• What is another name for the Krebs cycle?

  The citric acid cycle
• Who were the researchers that first described the metabolism of ketonic acids?

  Krebs and Johnson
• What does the term "amphibolic cycle" refer to in the context of the Krebs cycle?

  It involves both anabolic and catabolic processes
• What is produced when acetyl-CoA is catabolized in the Krebs cycle?

  2CO₂, ATP/GTP, and [H]
• What did the Miller-Urey experiment demonstrate?

  Biological building blocks form spontaneously
• What is the significance of the Arnon-Buchanan cycle?

  It operates in the reverse direction of the Krebs cycle
• Who proposed the iron-sulfur world hypothesis?

  1. Günter Wächtershäuser
• What is the role of coenzyme A in the Krebs cycle?

  It attaches acetyl-groups for metabolism
• How does the Krebs cycle differ in Eukaryia compared to most Bacteria?

  Eukaryia produces GTP, while Bacteria produce ATP
• What is the first step of the Krebs cycle?

  Acetyl-CoA combines with oxaloacetate
• What are the main products of the Krebs cycle in Eukaryia?

  • 2CO₂
  • GTP
  • 3NADH
  • QH₂
• What are the main steps of the Krebs cycle summarized?

  1. Acetyl-CoA + oxaloacetate → citrate
  2. Citrate → cis-aconitate
  3. Cis-aconitate → isocitrate
  4. Isocitrate → 2-oxoglutarate + CO₂ + NADH
  5. 2-oxoglutarate + CoA → succinyl-CoA + CO₂ + NADH
  6. Succinyl-CoA + GDP + Pᵢ → succinate + GTP + CoA
  7. Succinate → fumarate + QH₂
  8. Fumarate → malate
  9. Malate → oxaloacetate + NADH
• What is the role of citrate synthase in the Krebs cycle?

  It catalyzes the formation of citrate
• Why is aconitase significant in the Krebs cycle?

  It converts cis-aconitate to isocitrate
• What is the effect of fluoroacetate and fluorocitrate in the Krebs cycle?

  They are key inhibitors used for study
• What is the molecular weight of the pyruvate dehydrogenase complex in Homo sapiens?

  12.7 MDa
• What is the significance of the Warburg effect in cancer cells?

  It leads to an Arnon-Buchanan cycle
• How do the intermediates of the Arnon-Buchanan cycle compare to the Krebs cycle?

  They share most of the same intermediates
• What is the role of malate dehydrogenase in the Krebs cycle?

  It converts malate to oxaloacetate
• What is the function of succinyl-CoA synthetase?

  It converts succinyl-CoA to succinate
• How does the Krebs cycle contribute to cellular metabolism?

  It provides energy and building blocks
• What is the chemical formula for citrate?

  2-hydroxypropane-1,2,3-tricarboxylate
• What is the significance of substrate-channeling in the Krebs cycle?

  It enhances the efficiency of the cycle
• How do variations in the Krebs cycle affect energy production?

  They can alter ATP or GTP yield
• What are the cofactors involved in the Krebs cycle?

  Lipoate and thiamine pyrophosphate
• What is the significance of the size of the pyruvate dehydrogenase complex?

  It is five times the size of a ribosome
• How does Smith's horseshoe relate to the Krebs cycle?

  It is an evolutionary precursor to the cycle
• How do variations in the Krebs cycle manifest in different organisms?

  They affect energy currency production
• What are the substrates for the reaction involving cinyl-CoA?

  cinyl-CoA, CO₂, NADH
• What is the enzyme classification for the 2-oxoglutarate dehydrogenase complex?

  EC 1.2.1.105
• What is produced when succinyl-CoA reacts with GDP and Pᵢ?

  succinate, GTP, CoA
• What are the enzyme classifications for succinyl-CoA ligase?

  ATP = EC 6.2.1.4; GTP = EC 6.2.1.5
• What does succinate dehydrogenase convert succinate into?

  fumarate and QH₂
• What is the enzyme classification for fumarate hydratase?

  EC 4.2.1.2
• What is the product of malate when it is converted by malate dehydrogenase?

  oxaloacetate and NADH
• What are the key functions of citrate synthase in the Krebs cycle?

  • Rate-limiting step of the cycle
  • Adds 2C from acetyl-CoA to 4C oxaloacetate
  • Produces 6C citrate
  • Citrate is a tricarboxylic acid
• What is the significance of cis-aconitate in the aconitase reaction?

  It is transient and does not leave the active site
• What is fluoroacetate converted into in the Krebs cycle?

  fluoroacetyl-CoA and then fluorocitrate
• How does fluorocitrate affect aconitate hydratase?

  It permanently inhibits the enzyme
• What is the lethal dose of fluoroacetate for most Eukaryia?

  About 0.75 g to kill an adult male