Ch 17 Krebs Cycle 1

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  1. ·         Most of the ATP generated in metabolism is provided by the __, which starts with __ of glucose derivatives to __. This oxidation takes place in a series of reactions called the__, aka the__.
    o   It is the final common pathway for the __; and, most fuel molecules enter the cycle as __
    • aerobic processing of glucose
    • complete oxidation
    • carbon dioxide
    •  citric acid cycle
    •  TCA or Krebs Cycle
    • oxidation of fuel molecules
    • acetyl CoA
  2. ·         The __is the central metabolic hub of the cell, being the gateway to the __ of any molecule that can be transformed into an __ or a component of the __
    o   It is also an important source of __. __is important
    • CAC 
    • aerobic metabolism
    • acetyl group
    • CAC
    • precursors for the building blocks of mayn other molecules
    • Oxaloacetate
  3. ·         The function of the CAC is to include a __ that result in the __ to two molecules of __.
    o   This oxidation generates __ that will be used to power the __. The function of the CAC is the __
    • series of redox reactions
    • oxidation of an acetyl group
    • carbon dioxide
    • high-energy electrons
    • synthesis of ATP
    • harvesting of high-energy electrons from carbon fuels
  4. ·         Summary: a __ combines with a __ to yield a __, which releases CO2 twice in two successive oxidative decarboxylations that yield high-energy electrons
    o   A __ compound remains, which is further processed to regenerate __, which can initiate another round of the cycle
    §  Two carbon atoms enter the cycle as an acetyl unit and two carbons leave the cycle in the form of CO2
    • four carbon compound
    • two carbon acetyl unit
    • six-carbon tricarboxylc acid
    • four-carbon
    • oxaloacetate
  5. ·         The CAC removes electrons from __ and uses these electrons to form __ and __
    o   __ are transferred to three molecules of __ and __is transferred to one molecule of __.
    §  These electron carriers yield __ when they are oxidized by O2 in __, where electrons flow through proteins to generate a__ and __
    • acetyl CoA
    • NADH and FADH2
    • Three hydride ions (6 electrons)
    • NAD+
    • one pair of hydrogen atoms 
    • FAD
    • nine molecules of ATP
    • oxidative phosphorylation
    •  proton gradient and generate ATP
  6. ·         __initiates the first step in the citric acid cycle and is regenerated at the end of one passage through the cycle. Thus, one molecule of __is capable of participating in the oxidation of many acetyl molecules
    • Oxaloacetate 
    • oxaloacetate
  7. ·         Carbohydrates are processed by __ into __. Under anaerobic conditions, the __is converted into __ or __, depending on the organism
    o   Under aerobic conditions, the __is transported into __by a specific __ embedded in the __. In the matrix, __is __ by the __ to form __
    • glycolysis into pyruvate
    • pyruvate 
    • lactate or ethanol
    • pyruvate 
    • mitochondria 
    • carrier protein
    • mitochondrial membrane
    • pyruvate 
    • oxidatively decarboxylated
    • pyruvate dehydrogenase complex
    • acetyl CoA
  8. ·         This irreversible reaction is the link between __ and the __
    o   __ produces __and captures __ in the form of __
    §  Thus, the __ reaction has many of the key features of the reactions of the CAC itself
    • glycolysis and the CAC
    • Pyruvate dehydrogenase complex
    • CO2 
    • high-transfer-potential electrons
    • NADH
    • pyruvate dehydrogenase
  9. ·         The __ is a alrge, highly integrated complex of __; they are larger than __with molecular masses from 4 million to 10 million daltons. Their structures allow __, connected by __to the core of the structure
    ·         Conversion of __ to __ requires the participation of the __ of the __and __
    o   The coenzymes __, __, and __serve as catalytic cofactors, and __ and __ function as __
  10. pyruvate dehydrogenase complex
    • three distinct enzymes
    • ribosomes 
    • groups to travel from one active site to another
    • tethers
    • pyruvate to acetyl coA
    • three enzymes
    • pyruvate dehydrogenase complex 
    • five coenzymes
    • thiamine pyrophosphate (TPP)
    • lipoid acid
    • FAD 
    • CoA and NAD+
    • substrates
  11. ·         The conversion of pyruvate into acetyl CoA has three steps: __, __, and __, which must all be coupled to do what? 

    decarboxylation, oxidation, and transfer of the resultant acetyl group to CoA

    preserve the free energy derived from the decarboxylation step to drive the formation of NADH and acetyl CoA
  12. o Decarboxylation: __
    § This is catalyzed by __; __is the prosthetic group of the __
    pyruvate combines with TPP and is then decarboxylated to yield hydroxyethyl-TPP

    pyruvate dehydrogenase component of the multienzyme complex (E1)

    • TPP 
    • pyruvate dehydrogenase component
  13. o   Oxidation: __
    §  The oxidant in this reaction is the __, which is reduced to its __. This reaction, also catalyzed by the __, yields __
    The hydroxyethyl group attached to TPP is oxidized to form an acetyl group while being simultaneously transferred to lipoamide, a derivative of lipoic acid that is linked to the side chain of a lysine residue by an amide linkage. This transfer results in the formation of an energy-rich thioester bond

    • disulfide group of lipoamide
    • disulfyhydryl form
    • pyruvate dehydrogenase component E1
    • acetyllipoamide
  14. o   Formation of acetyl CoA. __

    · __catalyzes this reaction. The __ is preserved as the __ is transferred to __, which serves as a __of many activated acyl groups, of which acetyl is the simplest
    o __, the fuel for the CAC, is generated form pyruvate
    • The acetyl group is transferred from acetyllipamide to CoA to form acetyl CoA
    • Dihydrolipoyl transacetylase (E2) 
    • energy-rich thioester bond
    • acetyl group
    • CoA
    • carrier 
    • Acetyl CoA
  15. ·         The __ cannot complete another catalytic cycle unti what?
    ·         In a fourth step, the oxidized form of __is regenerated by __. Two electrons are transferred to an __prosthetic group of the enzyme and then to __
    o   This electron transfer from__ to __ is unusual because __. But, the __ of FAD is increased by its __, enabling it to __
    §  Proteins tightly associated with __ or __ are __
    • pyruvate dehydrogeanase complex
    • the dihydrolipamide is oxidized to lipoamide
    • lipoamide 
    • dihydrolipoyl dehydrogenase (E3)
    • FAD 
    • NAD+
    •  FAD to NAD+
    • FAD usually receives electrons
    • electron-transfer potential
    • chemical environment within the enzyme
    • transfer electrons to NAD+
    • FAD or FMN
    • flavoproteins
  16. ·         The core of the compelx is formed by the __
    o   __consists of __ assemble to form a hollow cube. Each of the three subunits forming a trimer has __major domains
    • transacetylase component E2
    • Transacetlyase 
    • 8 catalytic trimers
    • three
  17. §  At the amino terminus is a small domain that contains a __
    ·         It is homologous to __ like that of pyruvate carboxylase
    §  The __domain is followed by a small domain that interacts with __
    §  A  larger __ completes an E2 subunit
    • bound flexible lipoamide cofactor attached to a lysine residue
    • biotin-binding domains
    • lipoamide 
    • E3 within the complex
    • transacetylase domain
  18. o   E1 is an __, and E3 is an__. Multiple copies of E2 and E3 surround the E2 core
    §  The key to working together of all subunits is the__, which __
    alpha2beta2 tetramer

    alphabeta dimer

     flexible lipoamide arm of the E2 subunit

    carries substrate from active site to active site
  19. ·         Pyruvate is __at the active site of __, forming the __, and __leaves as the__
    o   This active site lies deep within the __, connected to the enzyme surface by a __
    o   __inserts the __ of the __ into the __leading to the active site
    • decarboxylated 
    • E1

    hydroxyethyl-TPP intermediate


    •  first product
    • E1 complex

    20-angstrom long hydrophobic channel


    • lipoamide arm
    • lipoamide domain

    deep channel I E1
  20. o   E1 catalyzes the __. The __then leaves E1 and enters the __ to visit the  __, located deep in the cube at the subunit interface
    o   The __ is then transferred to __, and the second product, __, leaves the cube. The reduced __ then swings to __
    • transfer of the acetyl group to the lipoamide
    • acetylated arm 
    • E2 cube
    • active site of E2
    • acetyl moiety
    • CoA
    • acetyl CoA
    • lipoamide arm
    • the active site of the E3 flavoprotein
  21. o   At the E3 active site, the __ is oxidized by__. The __ is ready to begin another reaction cycle
    o   The final product, __, is produced with the reoxidatoin of __to __
    • lipoamide is oxidized by coenzyme FAD
    • reactivated lipoamide
    • NADH
    • FADH2 to FAD
  22. ·         The structural integration of three kidns of enzymes and the long, flexible lipoamide arm make the __ possible.
    o   The __ increase the overall reaction rate and minimizes side reactions. All the intermediates in the oxidative decarboxylation of pyruvate remain __ throughout the reaction sequence and are readily transferred as the __ calls on each active site in turm
    • coordinated catalysis of a complex reaction
    • proximity of one enzyme to another
    • bound to the complex
    • flexible arm of E2
Card Set
Ch 17 Krebs Cycle 1
Test Four
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