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    The Citric Acid Cycle

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    Mohammed AlMujaini
    The document summarizes key topics about the citric acid cycle (CAC), also known as the Krebs cycle or tricarboxylic acid cycle. It discusses: 1) The CAC converts pyruvate to acetyl-CoA and provides precursors for biosynthesis through a series of reactions in the mitochondrion. 2) Key enzymes in the CAC include pyruvate dehydrogenase, citrate synthase, aconitase, isocitrate dehydrogenase, and malate dehydrogenase. 3) The CAC is regulated by oxygen, NADH, and substrate availability to balance energy production with biosynthesis.

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    The Citric Acid Cycle

    Uploaded by

    Mohammed AlMujaini
    124 views43 pages
    The document summarizes key topics about the citric acid cycle (CAC), also known as the Krebs cycle or tricarboxylic acid cycle. It discusses: 1) The CAC converts pyruvate to acetyl-CoA and provides precursors for biosynthesis through a series of reactions in the mitochondrion. 2) Key enzymes in the CAC include pyruvate dehydrogenase, citrate synthase, aconitase, isocitrate dehydrogenase, and malate dehydrogenase. 3) The CAC is regulated by oxygen, NADH, and substrate availability to balance energy production with biosynthesis.

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    The Citric Acid Cycle

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    The document summarizes key topics about the citric acid cycle (CAC), also known as the Krebs cycle or tricarboxylic acid cycle. It discusses: 1) The CAC converts pyruvate to acetyl-CoA and provides precursors for biosynthesis through a series of reactions in the mitochondrion. 2) Key enzymes in the CAC include pyruvate dehydrogenase, citrate synthase, aconitase, isocitrate dehydrogenase, and malate dehydrogenase. 3) The CAC is regulated by oxygen, NADH, and substrate availability to balance energy production with biosynthesis.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    124 views43 pages

    The Citric Acid Cycle

    Uploaded by

    Mohammed AlMujaini
    The document summarizes key topics about the citric acid cycle (CAC), also known as the Krebs cycle or tricarboxylic acid cycle. It discusses: 1) The CAC converts pyruvate to acetyl-CoA and provides precursors for biosynthesis through a series of reactions in the mitochondrion. 2) Key enzymes in the CAC include pyruvate dehydrogenase, citrate synthase, aconitase, isocitrate dehydrogenase, and malate dehydrogenase. 3) The CAC is regulated by oxygen, NADH, and substrate availability to balance energy production with biosynthesis.

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    Chapter 16

    The Citric Acid Cycle: CAC Krebs Cycle Tricarboxylic Acid Cycle: TCA

    The Citric Acid Cycle

    Key topics: To Know


    Also called Tricarboxylic Acid Cycle (TCA) or Krebs Cycle. Three names for the same thing. Cellular respiration and intermediates for biosynthesis. Conversion of pyruvate to activated acetate Reactions of the citric acid cycle Anaplerotic reactions to regenerate the acceptor Regulation of the citric acid cycle Conversion of acetate to carbohydrate precursors in the glyoxylate cycle

    Discovered CAC in Pigeon Flight Muscle

    Cellular Respiration Process in which cells consume O2 and produce CO2 Provides more energy (ATP) from glucose than Glycolysis Also captures energy stored in lipids and amino acids Evolutionary origin: developed about 2.5 billion years ago Used by animals, plants, and many microorganisms Occurs in three major stages: - acetyl CoA production (This chapter) - acetyl CoA oxidation (This chapter) - electron transfer and oxidative phosphorylation (Chapter 19)

    Overall Picture

    Overall Picture

    The area blocked off all takes place in the Mitochondrion. So, first pyruvate has to get transported from the cytoplasm into the mitochondrion. In this Figure, only Glycolysis is in the Cytoplasm.

    Acetyl-CoA production occurs in the mitochondria. Acetyl-CoA enters the CAC.

    Pyr DH is a Complex Enzyme

    Pyruvate Dehydrogenase

    Model

    TEM

    Lipoic Acid is linked to a Lys (K)

    Remember HSCoA ? from Chapter 1

    It is down here

    One Unit of Pyr DH

    EOC Problem 6: Tests your knowledge of PyrDH. EOC Problem 7: Thiamin deficiency and blood pyruvate.

    Pyr DH is a Cool Enzyme

    EOC Problem 5: NAD+ in oxidation and reduction reactions (a through f should be easy).

    Citrate Synthase
    Convention to write incoming Acetyl on Top

    EOC Problem 32, further on the thermodynamics of Citrate Synthase.

    Aconitase, the Ferris Wheel

    The Aconitase Iron Sulfur Complex

    Aconitase has More than One Role


    Mitochondrial aconitase: Citric Acid Cycle Cytosolic aconitase: 2 roles: 1. citrate isocitrate 2. iron response regulator

    Aconitase binding iron/RNA

    To become an iron response regulator, aconitase changes it shape (due to lack of iron) so it can bind RNA.

    Isocitrate DH

    Go = -21 kJ/mole Mn++ cofactor EOC Problem 8 is all about IsocitDH.

    KG DH is Just Like Pyr DH

    TPP, lipoate FAD

    Succinyl CoA Synthetase : Substrate Level Phosphorylation

    One GTP = One ATP

    Nucleoside diphosphate kinase:


    G o = 0

    GTP + ADP GDP + ATP

    Succinate DH = Old Yellow

    Malonate was One of the First Competitive Inhibitors Known

    Fumarase: the addition of water in two parts

    Dont Confuse Malate and Maleate

    Malate DH is Endothermic

    CAC Energetics

    Watch Where the Label Goes

    EOC Problem 18: Labeled glucose carbons and where they go in CAC.

    Citrate is Prochiral

    The Acetyl Portion does not get oxidized to CO2 Until the Second Round

    And it gets randomized at Succinate

    Energetics of Glycolysis and CAC in ATPs

    EOC Problems 1 and 2: Balanced equations for Glycolysis and CAC.

    CAC in Anaerobic Not-Respiratory Organisms

    Its a 2 input FORK

    This is Why

    OAA D, N, I, K, T, M

    Anaplerotic Reactions

    Regulation of CAC

    EOC Problem 30 and 31 on oxygen and NAD regulation of CAC.

    Pathway Proteins Form Functional Units but Its Concentration Dependent

    Pathways are Protein Modules


    Flagella LPS Outer Membrane Peptidoglycan

    Cytoplasmic Membrane
    Glycolysis

    ATPase

    RNA

    In Animals CAC can not be used for Gluconeogensis from Ac-SCoA

    D, N, L, K, M, T, I

    Porphrins: heme (cytochromes, hemoglobin), chlorophyll

    E, Q, P, R

    In Bacteria and Plants, Not Vertebrates


    Overall: 2 Ac-SCoA Succinate

    Succinate OAA

    NADH and FADH2

    Oxaloacetate

    CAC

    Glyoxylate Cycle in Plants in a Membrane Body

    Linkage to Gluconeogenesis in Plants

    Regulation Linkage

    Things to Know and Do Before Class


    1. Pyruvate DHall three parts and cofactors. 2. Chemistry of each step in Citric Acid Cycle. 3. Overall CAC thermodynamics (which steps are at Eq and which are drivers. 4. Prochiral nature of citrate. 5. Amphibolic nature of CAC and why fermenters need almost all of CAC. 6. Importance of anaplerotic reactions and how they work. 7. Glyoxylate Cycle (mammals lack) but plants, some invertebrates and bacteria have it. What does it do? 8. EOC Problems 1-9, 16, 18, 19, 30-32.

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