Kreb's cycle (1)
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Kreb's cycle (1)

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BIOCHEM WK 3

BIOCHEM WK 3

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Kreb's cycle (1) Kreb's cycle (1) Presentation Transcript

  • KREB’S CYCLE (TRICARBOXYLIC ACID (TCA)CYCLE/CITRIC ACID CYCLE) BIOCHEMISTRY LEC WEEK 3
  • METABOLIC PATHWAYS
    • A series of consecutive biochemical reactions catalyzed by enzymes that produce a specific end product.
    • Catabolism- the breakdown of food stuffs to simple organic chemicals.
    • Anabolism- the synthesis of biomolecules from simple organic chemicals.
  • METABOLIC PATHWAYS
    • Very Few metabolites are used to synthesize a large variety of biomolecules :
    • Acetyl-Coenzyme A (acetyl-CoA)
    • Pyruvate
    • Citrate acid cycle intermediates
  • METABOLIC PATHWAYS
    • Three main pathways for energy production:
    • Glycolysis
    • Citric acid cycle
    • Oxidative-Phosphorylation
  • METABOLIC PATHWAYS
    • Certain pathways are involved in both breakdown and buildup of molecules these pathways are called amphibolic . The citric acid cycle is an example of this.
  • OVERALL GOAL/IMPORTANCE
    • Makes ATP
    • Makes NADH
    • Makes FADH 2
    • A cyclical series of biochemical reactions that is fundamental to the metabolism of aerobic organisms, i.e. animals, plants, and many microorganisms
  • Geography
    • Krebs in mitochondrial matrix
    • Mitochondrion
      • Outer membrane very permeable
        • Space between membranes called intermembrane space
      • Inner membrane (cristae)
        • Permeable to pyruvate,
        • Impermeable to fatty acids, NAD, etc
      • Matrix is inside inner membrane
  • The citric acid cycle enzymes are found in the matrix of the mitochondria
  • OVERVIEW
    • Described by Hans Adolf Krebs in 1937
    • A feature of cell chemistry shared by all types of life.
    • A complex series of reactions beginning and ending with the compound oxaloacetate.
    • The cycle produces carbon dioxide and the energy-rich compound ATP.
  • OVERVIEW
    • Eight successive reaction steps.
    • The six carbon citrate is formed from two carbon acetyl-CoA and four carbon oxaloacetate.
    • Oxidation of citrate yields CO2 and regenerates oxaloacetate.
    • The energy released is captured in the reduced coenzymes NADH and FADH2.
  • Conversion of pyruvate to Acetyl CoA
    • 2 per glucose (all of Kreb’s)
    • Oxidative decarboxylation
    • Makes NADH
  • Fates of Acetyl CoA
    • In the presence of CHO
      • Metabolized to CO 2 , NADH, FADH 2 ,GTP and, ultimately, ATP
    • If energy not being used (Lots of ATP present)
      • Made into fat
    • If energy being used, but no CHO present
      • Starvation
      • Forms ketone bodies (see fat metabolism slides)
      • Danger!
  • Kreb’s Cycle
  • 1. Citrate Synthase Reaction
  • 2. Aconitase Reaction
    • Forms isocitrate
  • 3. Isocitrate Dehydrogenase
    • All dehydrogenase reactions make NADH or FADH 2
  • 4. α -ketoglutarate dehydrogenase
    • Same as pyruvate dehydrogenase reaction
  • 5. Succinyl CoA synthetase
    • Coupled to synthesis of GTP
      • GTP very similar to ATP and interconverted later
  • 6. Succinate dehydrogenase
    • Dehydrogenation
    • Uses FAD
  • 7. Fumarase
    • Addition of water to a double bond
  • 8. Malate Dehydrogenase
    • Makes NADH
    • Regenerates oxaloacetate for another round
  • Net From Kreb’s
    • Oxidative process
      • 3 NADH
      • FADH 2
      • GTP
    • X 2 per glucose
      • 6 NADH
      • 2 FADH 2
      • 2 GTP
    • All ultimately turned into ATP (oxidative phosphorylation)