Citric Acid Cycle

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pebbles135
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46328
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Citric Acid Cycle
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2010-10-31 18:33:48
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Biochemblock3
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Biochem block3 Lecture 30 Chapter 9
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  1. What is aerobic metabolism?
    Aerobic organisms use an oxygen-requiring process to produce ATP
  2. Where is the location of the citric acid cycle?
    The citric acid cycle, the ETC, and oxidative phosphorylation all take place in the mitochondria
  3. Describe the structure of mitochondria:
    Mitochondria has an outer membrane, inner membrane, and matrix within the inner membrane
  4. What are the general rxns involved in the citric acid cycle?
    • Oxidation and Reduction
    • Redox
  5. What are the starting molecules of the citric acid cycle?
    • Acetyl-CoA (after formed from pyruvate)
    • The acetyl group enters the cycle by reacting with oxaloacetate
  6. Which rxns of the citric acid cycle involve the reduction of coenzymes?
    • Step 3: Isocitrate dehydrogenase converts Isocitrate to alpha-ketoglutarate which reduces NAD+ to NADH
    • Step 4: alpha-Ketoglutarate dehydrogenase complex converts alpha-ketoglutarate to succinyl-CoA which reduces NAD+ to NADH and makes co2
    • Step 6: Succinate dehydrogenase converts succinate to fumarate which reduces FAD to FADH2
    • Step 8: Malate dehydrogenase converts malate to oxaloacetate (OAA) which reduces NAD+ to NADH
  7. Which rxn in the citric acid cycle releases CO2?
    • Step 3: Isocitrate dehydrogenase converts Isocitrate to alpha-ketoglutarate which reduces NAD+ to NADH and makes CO2
    • Step 4: alpha-Ketoglutarate dehydrogenase complex converts alpha-ketoglutarate to succinyl-CoA which reduces NAD+ to NADH and makes co2
  8. Which process produce energy (substrate level phosphorylation) during the citric acid cycle?
    Step 5: Succinate thiokinase converts succinyl-CoA to succinate and mainly makes one molecule of GTP which can be used to make ATP.
  9. What happens to electrons produced during the Citric Acid Cycle?
    • Electrons are captured during a number of metabolic reactions and shuttled via coenzymes to the electron transport chain (ETC)
    • The CAC produces lrg # of electrons for the ETC.
  10. What does oxidative phosphorylation involve?
    O2 as an electron acceptor
  11. Electrons go from a___to an ___
    Electrons go from a donor (reducing agent) to an acceptor (oxidizing agent)
  12. When a molecule loses electrons, it is
    Oxidized
  13. When a molecule gains electrons, it is
    Reduced
  14. What does NAD stand for?
    • Nicotinamide adenine dinucleotide (Aerobic respiration)
    • Can donate or accept 1 Hydride ion
  15. What does NADP stand for?
    • Nicotinamide adenine dinucleotide phosphate (Photosynthesis)
    • Can donate or accept 1 Hydride ion
  16. What is riboflavin part of?
    • Vitamin B2 is part of both:
    • Flavin mononucleotide (FMN)
    • Flavin adenine dinucleotide (FAD)
  17. Which coezymes can accept and donate (maybe 1 at a time) 2 Hydride ions?
    FADH2 and FMNH2
  18. How are reduced molecules used during aerobic respiration?
    Reduced molecules (like NADH) can be used to drive the production of ATP in aerobic respiration
  19. Why is the CAC considered a cycle?
    It is a cycle because the starting material (oxaloacetate) is regenerated each round
  20. Generally define the CAC?
    • Series of reactions in mitochondria used to release energy in acetyl-CoA
    • The overall process involves the reduction of several coenzymes and the release of CO2
  21. What is the Net rxn of CAC?
    • Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 2H2O -->
    • 2CO2 + 3 NADH + FADH2 + CoASH + GTP + 2H
  22. What are the coenzymes of CAC?
    • Thiamine pyrophosphate (TPP) – part of pyruvate decarboxylase
    • Lipoic acid – part of dihydrolipoyl transacetylase
    • NADH– electron carrier
    • FADH2 –electron carrier
    • Coenzyme A (CoASH) – acetyl group carrier
  23. What is the main function of Coenzyme A?
    • Acetyl group carrier by means of attachment to its sulfur
    • Abbreviated CoASH when not attached to anything
    • The acetyl group transferred to CoASH by means of the pyruvate dehydrogenase complex
  24. How is pyruvate transferred to Acetyl-CoA?
    Using the Pyruvate dehydrogenase complex
  25. What is the Pyruvate dehydrogenase complex?
    A large multi-enzyme complex that catalyzes the process of converting pyruvate into an acetyl group on CoA; functions inside mitochondrial matrix
  26. What is the Pyruvate dehydrogenase complex made of?
    • Made of three separate enzymes:
    • Pyruvate dehydrogenase (E1) – decarboxylates pyruvate (which is bound to TPP)
    • Dihydrolipoyl transacetylase (E2) – transfer of acetyl group to CoASH
    • Dihydrolipoyl dehydrogenase (E3) – reoxidizes dihydrolipoamide (lipoic acid bound to lysine; involves reduction of NAD+)
  27. Describe the 5 steps involved with pyruvate dehydrogenase?
    • First, pyruvate becomes bonded to TPP
    • Second, pyruvate is decarboxylated
    • Third, the acetyl group is transferred to lipoic acid
    • Fourth, the acetyl group is transferred to CoASH
    • Fifth, lipoic acid is reoxidized
  28. Describe the CAC into 2 stages:
    • The acetyl group enters the cycle by reacting with oxaloacetate, and two molecules of CO2 are released (reactions 1-4)
    • Oxaloacetate is regenerated in order to react again with acetyl-CoA (reactions 5-8)

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