Bioenergetics Overview and TCA Cycle
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Questions and Answers

What role does acetyl-CoA play in metabolism?

  • It acts as a key metabolite at the crossroads of intermediate metabolism. (correct)
  • It is involved exclusively in anaerobic respiration.
  • It is the primary energy source for cellular respiration.
  • It serves as a carrier for fatty acids in the mitochondria.
  • Which mechanism is described as involving chemiosmotic coupling in the context of bioenergetics?

  • Photophosphorylation
  • Oxidative phosphorylation (correct)
  • Substrate level phosphorylation
  • Glycolytic pathway interactions
  • What is a potential consequence of cyanide poisoning related to the mitochondrial respiratory chain?

  • It enhances the overall efficiency of ATP production.
  • It disrupts electron transfer within the respiratory chain. (correct)
  • It activates uncoupling proteins to enhance metabolism.
  • It increases the production of acetyl-CoA.
  • Why are transport systems necessary for the exchange of metabolites between mitochondria and cytosol?

    <p>Some metabolites cannot diffuse across the mitochondrial membrane.</p> Signup and view all the answers

    How does the regulation of the pyruvate dehydrogenase complex (PDH) affect metabolic pathways?

    <p>It controls the entry of pyruvate into the tricarboxylic acid cycle.</p> Signup and view all the answers

    What is the primary metabolic fate of acetyl-CoA in the tricarboxylic acid cycle?

    <p>Complete oxidation to CO2</p> Signup and view all the answers

    Which reducing equivalents are produced as a result of the reactions in the tricarboxylic acid cycle?

    <p>NADH and FADH2</p> Signup and view all the answers

    What is generated from the energy-rich thioester linkage in succinyl-CoA during the TCA cycle?

    <p>GTP</p> Signup and view all the answers

    How many carbon atoms enter the tricarboxylic acid cycle from acetyl-CoA?

    <p>Two</p> Signup and view all the answers

    Which compound is formed as citrate is converted into isocitrate in the TCA cycle?

    <p>Cis-aconitate</p> Signup and view all the answers

    What is the primary consequence of pyruvate dehydrogenase deficiency in children?

    <p>Chronic lactic acidosis</p> Signup and view all the answers

    Which of the following is NOT a symptom associated with pyruvate dehydrogenase deficiency?

    <p>Heart enlargement</p> Signup and view all the answers

    What dietary management is recommended for patients with pyruvate dehydrogenase deficiency?

    <p>Ketogenic diet</p> Signup and view all the answers

    How is pyruvate dehydrogenase deficiency diagnosed?

    <p>PDH activity in cultured skin fibroblasts</p> Signup and view all the answers

    Which treatment option helps to prevent the inactivation of the pyruvate dehydrogenase complex?

    <p>Dichloroacetate</p> Signup and view all the answers

    What condition is directly caused by thiamine deficiency?

    <p>Beri-beri</p> Signup and view all the answers

    What metabolic consequence is primarily associated with the functioning of pyruvate dehydrogenase?

    <p>Production of acetyl-CoA</p> Signup and view all the answers

    Which of the following is a key neurological symptom of pyruvate dehydrogenase deficiency?

    <p>Seizures</p> Signup and view all the answers

    Which clinical trial treatment is currently being investigated for PDH deficiency?

    <p>Dichloroacetate</p> Signup and view all the answers

    What are the elevated metabolites found in children with pyruvate dehydrogenase deficiency?

    <p>Pyruvate and alanine</p> Signup and view all the answers

    Study Notes

    Bioenergetics Overview

    • Bioenergetics involves three stages of metabolism: glycosis, the TCA cycle, and oxidative phosphorylation.
    • The pyruvate dehydrogenase (PDH) complex catalyzes the conversion of pyruvate to acetyl-CoA, crucial for energy metabolism.
    • The TCA cycle, also known as the Krebs cycle, oxidizes acetyl-CoA to CO2, producing NADH and FADH2 for ATP generation through oxidative phosphorylation.

    Oxidative Phosphorylation

    • Chemiosmotic coupling is the mechanism for ATP synthesis in oxidative phosphorylation.
    • Inhibitors and uncouplers can impair ATP production by disrupting electron flow and H+ gradient.
    • Sites of oxidative phosphorylation include the mitochondrial respiratory chain complexes where electron transfer occurs.

    The Tricarboxylic Acid Cycle (TCA)

    • The TCA cycle generates reducing equivalents (NADH, FADH2) and one GTP per cycle.
    • Completion of the cycle results in the release of two CO2 molecules and the generation of energy-rich compounds.
    • Regulation of the TCA cycle is vital due to its involvement in cellular energy production and macromolecule synthesis.

    Clinical Correlations

    • PDH Deficiency: Genetic defects can lead to elevated lactate, pyruvate, and alanine levels, resulting in lactic acidosis and neurological issues.
    • Beri-Beri: Caused by thiamine (vitamin B1) deficiency, resulting in neurological and cardiovascular symptoms, such as edema and heart enlargement.
    • Therapeutics for PDH deficiency include ketogenic diets and agents like dichloroacetate to maintain PDH activity.

    Mitochondrial Respiratory Chain

    • Contains complexes and mobile carriers that facilitate electron transfer, leading to ATP production.
    • Direction of electron transfer is crucial for the efficient functioning of the respiratory chain.
    • Cyanide poisoning inhibits the respiratory chain, blocking ATP synthesis and causing cellular dysfunction.

    Mitochondrial Transport Systems

    • The outer mitochondrial membrane is permeable to smaller solutes, while the inner membrane is highly selective and impermeable to NAD+, NADH, and other nucleotides.
    • Specific transport proteins allow metabolites to cross the inner membrane, ensuring efficient metabolic exchange between mitochondria and cytosol.
    • Distinct carrier systems prevent the transport of closely related molecules, ensuring specificity in mitochondrial function.

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    Description

    This quiz covers key concepts in bioenergetics, focusing on the three stages of metabolism: glycolysis, the TCA cycle, and oxidative phosphorylation. It examines the mechanisms of ATP synthesis and the role of the pyruvate dehydrogenase complex, along with the importance of electron transfer in generating energy-rich compounds.

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