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Questions and Answers

What is the result of thiamine (vitamin B1) deficiency?

  • Increased activity of pyruvate dehydrogenase
  • Inhibition of enzymes requiring TPP as a coenzyme (correct)
  • Enhanced glucose oxidation
  • Decrease in blood pyruvate levels

    • What is a common symptom of the disease caused by TPP deficiency?

  • Digestive problems
  • Respiratory issues
  • Neurological and cardiovascular disorder (correct)
  • Skin rashes

    • What clever chemistry allows living organisms to oxidize acetate in the TCA cycle?

  • Condensation with oxalacetate followed by b-cleavage (correct)
  • Formation of acetyl-CoA without condensing reactions
  • Direct oxidation of acetate without any cleavage
  • Condensation with pyruvate followed by a-cleavage

    • How can thiamine deficiency be detected in the blood?

    <p>Low enzyme activity, especially transketolase</p> Signup and view all the answers

    Which food could help treat thiamine deficiency?

    <p>Unpolished rice</p> Signup and view all the answers

    What is the role of aconitase in the citric acid cycle?

    <p>It catalyzes the conversion of citrate to isocitrate.</p> Signup and view all the answers

    Why cannot tertiary alcohols be oxidized easily in the citric acid cycle?

    <p>They cannot form a carbon-oxygen bond without breaking a carbon-carbon bond.</p> Signup and view all the answers

    What type of alcohol is isocitrate classified as?

    <p>Secondary alcohol</p> Signup and view all the answers

    What is the intermediate formed during the conversion of citrate to isocitrate?

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

    How does citrate interact with citrate synthase in the citric acid cycle?

    <p>It acts as a substrate.</p> Signup and view all the answers

    What characterizes ATP despite being labeled as a high-energy compound?

    <p>It is kinetically stable.</p> Signup and view all the answers

    Which of the following best describes the nature of ATP breakdown?

    <p>It typically involves synthesis of glucose-6-phosphate.</p> Signup and view all the answers

    What does the hexokinase reaction specifically involve?

    <p>Nucleophilic attack of glucose on the γ-phosphate of ATP.</p> Signup and view all the answers

    What happens to carbon atoms during oxidation in organic compounds?

    <p>They lose shared electrons associated with C-H bonds.</p> Signup and view all the answers

    What illustrates the term 'high phosphoryl group transfer potential' in ATP?

    <p>Strength of phosphate bonds during reactions.</p> Signup and view all the answers

    How do carbon atoms become oxidized during the respiratory chain process?

    <p>By losing both protons and electrons.</p> Signup and view all the answers

    What effect does the nucleophilic attack in hexokinase have?

    <p>It facilitates glucose phosphorylation.</p> Signup and view all the answers

    Which of the following statements is incorrect about high-energy compounds like ATP?

    <p>They are always chemically unstable.</p> Signup and view all the answers

    What inhibits the activity of the pyruvate dehydrogenase complex (PDC)?

    <p>Acetyl-CoA and NADH</p> Signup and view all the answers

    Which enzyme is responsible for the formation of oxaloacetate in the TCA cycle?

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

    Which of the following pathways contributes to replenishing TCA cycle intermediates?

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

    Which amino acids are NOT typically associated with the TCA cycle through anaplerotic reactions?

    <p>Methionine and Arginine</p> Signup and view all the answers

    What is the primary role of the TCA cycle in relation to other metabolic pathways?

    <p>Providing precursors for biosynthetic processes</p> Signup and view all the answers

    Which compound enters the TCA cycle at the level of succinyl-CoA?

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

    What is the $ riangle G^o$ value for the hydrolysis of the thioester bond of Acetyl-CoA?

    <p>-31.5 KJ/mol</p> Signup and view all the answers

    Which functional group is found in the thiazolium ring of thiamine (TPP)?

    <p>Thiazole ring</p> Signup and view all the answers

    What is succinyl-CoA classified as in the TCA cycle?

    <p>A high-energy intermediate</p> Signup and view all the answers

    Which phosphorylation occurs with succinyl-CoA in mammals during the TCA cycle?

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

    Which molecule is coupled with the formation of GTP in mammals when utilizing succinyl-CoA?

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

    What is the role of the enzyme succinyl-CoA synthetase in the TCA cycle?

    <p>Catalyze the transfer of a phosphoryl group</p> Signup and view all the answers

    Which of the following correctly describes the first step in the reaction catalyzed by succinyl-CoA synthetase?

    <p>Formation of succinyl phosphate</p> Signup and view all the answers

    In which type of organisms does succinyl-CoA lead to ADP being converted to ATP?

    <p>Only in plants</p> Signup and view all the answers

    What is produced when GTP exchanges its terminal phosphoryl group with ADP?

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

    Which cofactor is covalently bound to succinate dehydrogenase?

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

    Which of the following steps takes place after the formation of phosphoryl-His in the reaction catalyzed by succinyl-CoA synthetase?

    <p>Transfer of the phosphoryl group to GDP</p> Signup and view all the answers

    What is the final product of the reaction involving succinyl-CoA in mammals?

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

    What is produced during the conversion of succinyl CoA in the TCA cycle?

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

    Which molecule is directly generated from isocitrate in the TCA cycle?

    <p>a-Ketoglutarate</p> Signup and view all the answers

    Which of the following components is oxidized during the conversion of succinate to fumarate?

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

    What molecule enters the TCA cycle combining with oxaloacetate?

    <p>Acetyl CoA</p> Signup and view all the answers

    What is the role of NAD+ in the TCA cycle?

    <p>It serves as an electron transport molecule.</p> Signup and view all the answers

    Which compound is produced from the hydration of fumarate?

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

    What happens to carbon atoms during the TCA cycle?

    <p>They are released in the form of CO2.</p> Signup and view all the answers

    Which process is primarily associated with GTP production in the TCA cycle?

    <p>Conversion of succinyl CoA</p> Signup and view all the answers

    What is the immediate precursor of ATP or GTP in the TCA cycle?

    <p>Succinyl CoA</p> Signup and view all the answers

    Which coenzyme participates in oxidation during the conversion of succinate?

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

    What is the role of magnesium ions in the reaction involving ATP investment?

    <p>They stabilize the negative charges of the ATP molecule.</p> Signup and view all the answers

    Which aspect of ATP is crucial for its function as an energy molecule?

    <p>The high phosphoryl group transfer potential.</p> Signup and view all the answers

    Why is the nucleophilic attack of glucose on ATP considered irreversible?

    <p>It releases a significant amount of energy.</p> Signup and view all the answers

    What is the first step in the reaction involving glucose and ATP?

    <p>Nucleophilic attack of glucose on the γ-phosphate of ATP.</p> Signup and view all the answers

    What aspect of ATP's structure increases its electrophilicity during nucleophilic attack?

    <p>The chelation with magnesium ions.</p> Signup and view all the answers

    What type of reaction occurs during the conversion of glucose 6-phosphate to fructose 6-phosphate?

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

    What must occur to glucose 6-phosphate before isomerization can take place?

    <p>Its cyclic form must be opened.</p> Signup and view all the answers

    What characterizes the new carbonyl position after the isomerization of glucose 6-phosphate?

    <p>It becomes a ketone at C-2.</p> Signup and view all the answers

    What facilitates the subsequent C-C bond cleavage in glycolysis after isomerization?

    <p>Activation of C-3.</p> Signup and view all the answers

    What distinguishes an aldose from a ketose in the context of carbohydrates?

    <p>The position of the carbonyl group.</p> Signup and view all the answers

    Which enzyme catalyzes the isomerization of glucose 6-phosphate to fructose 6-phosphate?

    <p>Phosphoglucose isomerase</p> Signup and view all the answers

    What type of carbon structure is formed from fructose 6-phosphate after the isomerization process?

    <p>Five-membered ring</p> Signup and view all the answers

    Which functional group is highlighted as becoming a new feature at C-1 after the isomerization of glucose 6-phosphate?

    <p>Primary alcohol group</p> Signup and view all the answers

    What role does hexokinase play in glucose metabolism?

    <p>It phosphorylates glucose, initiating glycolysis.</p> Signup and view all the answers

    Which of the following statements is true regarding hexokinases?

    <p>Hexokinases consist of tissue-specific isoenzymes.</p> Signup and view all the answers

    What is the product of the enzymatic reaction catalyzed by aldolase?

    <p>Glyceraldehyde 3-phosphate.</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate?

    <p>Phosphofructokinase.</p> Signup and view all the answers

    What distinguishes different hexokinases from each other?

    <p>Their tissue localization and kinetic properties.</p> Signup and view all the answers

    What intermediate is formed during the phosphorylation of glucose?

    <p>Glucose 6-phosphate.</p> Signup and view all the answers

    What is the main function of phosphoglucoisomerase in glycolysis?

    <p>To convert glucose 6-phosphate into fructose 6-phosphate.</p> Signup and view all the answers

    Which of the following best describes the glycolytic pathway's initial phase?

    <p>It requires the input of ATP.</p> Signup and view all the answers

    What is the net yield of ATP per mole of glucose during glycolysis?

    <p>2 mol</p> Signup and view all the answers

    How many moles of NADH are produced per mole of glucose during glycolysis?

    <p>2 mol</p> Signup and view all the answers

    What indicates that a reaction is thermodynamically favored during glycolysis?

    <p>Negative ΔG</p> Signup and view all the answers

    During the ATP-generating phase of glycolysis, how many moles of triose phosphate are formed?

    <p>2 mol</p> Signup and view all the answers

    What is the change in free energy represented by ΔG in the context of glycolysis?

    <p>ΔG = ΔH - TΔS</p> Signup and view all the answers

    Which substances are produced alongside 2 moles of pyruvate from the glycolysis of one mole of glucose?

    <p>2 NADH and 4 ATP</p> Signup and view all the answers

    What characterizes the three large negative standard free-energy changes in glycolysis?

    <p>They are all irreversible processes.</p> Signup and view all the answers

    Which of the following statements about glycolysis is incorrect?

    <p>Glycolysis occurs in the mitochondrial matrix.</p> Signup and view all the answers

    What two phosphorylated three-carbon compounds are generated from the aldol cleavage of fructose 1,6-bisphosphate?

    <p>Glyceraldehyde 3-phosphate and Dihydroxyacetone phosphate</p> Signup and view all the answers

    Which enzyme catalyzes the cleavage of fructose 1,6-bisphosphate into triose phosphates?

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

    What type of reaction mechanism does aldolase utilize in the forward direction?

    <p>Aldol cleavage</p> Signup and view all the answers

    What role does the lysine ε-amino group play in the aldolase reaction?

    <p>Provides nucleophilic attack on the keto carbon</p> Signup and view all the answers

    Which of the following correctly describes the activity of aldolase in the metabolic pathway?

    <p>Converts DHAP into Glyceraldehyde 3-phosphate</p> Signup and view all the answers

    During which phase of glycolysis does aldol cleavage occur?

    <p>Energy Investment Phase</p> Signup and view all the answers

    Which sugar is isomerized to form Glyceraldehyde 3-phosphate?

    <p>Dihydroxyacetone phosphate</p> Signup and view all the answers

    What is the main function of aldolase in glycolysis?

    <p>To split fructose 1,6-bisphosphate into triose phosphates</p> Signup and view all the answers

    What is the primary product of glycolysis after the oxidation of glucose 6-phosphate?

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

    Which shuttle is involved in transferring reducing equivalents from cytosolic NADH to the electron-transport chain?

    <p>Glycerol 3-phosphate shuttle</p> Signup and view all the answers

    What is the net gain of ATP from one molecule of glucose during glycolysis?

    <p>Two molecules of ATP</p> Signup and view all the answers

    In which cellular location does glycolysis occur?

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

    What is produced as a result of pyruvate oxidation by pyruvate dehydrogenase?

    <p>Acetyl-CoA</p> Signup and view all the answers

    Approximately how many molecules of ATP can be generated from the complete aerobic oxidation of one molecule of glucose?

    <p>30 to 32 mol of ATP</p> Signup and view all the answers

    What is the first step in glycolysis that involves the phosphorylation of glucose?

    <p>Conversion of glucose to glucose 6-phosphate</p> Signup and view all the answers

    How is the reducing equivalent from NADH generated during glycolysis transport across the inner mitochondrial membrane?

    <p>Malate-aspartate shuttle or glycerol 3-phosphate shuttle</p> Signup and view all the answers

    What type of polysaccharide is cellulose?

    <p>Structural polysaccharide</p> Signup and view all the answers

    Which form of starch is more branched and preferred for storage in plants?

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

    What structural linkages characterize glycogen?

    <p>1-4 linkages and 1-6 linkages</p> Signup and view all the answers

    Why is cellulose indigestible for most animals?

    <p>Animals do not have the enzyme to break it down</p> Signup and view all the answers

    What is the primary function of starch in plants?

    <p>Energy storage</p> Signup and view all the answers

    Which form of glucose is primarily found in cellulose?

    <p>β-glucose</p> Signup and view all the answers

    What distinguishes amylose from amylopectin?

    <p>Amylose is linear, while amylopectin is branched</p> Signup and view all the answers

    What type of molecules does glycogen primarily serve as in animals?

    <p>Energy storage molecules</p> Signup and view all the answers

    What does the Km of an enzyme indicate?

    <p>The concentration of substrate required to reach half of Vmax</p> Signup and view all the answers

    Which type of allosteric interaction occurs when effectors are different from substrate molecules?

    <p>Heterotropic interaction</p> Signup and view all the answers

    What shape does the plot of an allosteric interaction typically exhibit?

    <p>Sigmoid plot</p> Signup and view all the answers

    What is the main function of the urea cycle?

    <p>Prevent NH4+ toxicity by converting NH4+ to urea</p> Signup and view all the answers

    When is Vmax of an enzyme typically achieved?

    <p>At an infinite concentration of substrate</p> Signup and view all the answers

    Which regulatory mechanism allows for changes in enzyme activity through specific chemical modifications?

    <p>Covalent modification</p> Signup and view all the answers

    What does a rectangular hyperbola graph represent in enzyme kinetics?

    <p>The enzyme's saturation behavior at varying substrate levels</p> Signup and view all the answers

    Which of the following best describes the role of isoenzymes?

    <p>They catalyze the same reaction but differ in properties and regulation</p> Signup and view all the answers

    What happens to the Φ and Ψ angles as the carbonyl or amide nitrogens rotate clockwise?

    <p>They increase.</p> Signup and view all the answers

    What factors can influence the rotational hindrance of bonds in the backbone?

    <p>Size and charge of R groups.</p> Signup and view all the answers

    What do aromatic amino acids potentially generate when arranged in a specific way?

    <p>Forces leading to stabilization of protein architecture.</p> Signup and view all the answers

    In what state can R groups be depending on their environment?

    <p>Either protonated or deprotonated based on pH.</p> Signup and view all the answers

    What angle is observed when the Φ and Ψ angles are at their maximum in the given conformation?

    <p>180°.</p> Signup and view all the answers

    What defines the primary roles of metabolism in biological systems?

    <p>Generation of energy and synthesis of biological molecules</p> Signup and view all the answers

    How do catabolic pathways differ from anabolic pathways?

    <p>Catabolic pathways release energy while anabolic pathways consume energy.</p> Signup and view all the answers

    What role do the sizes and charges of R groups play in conjunction with single bonds in the backbone?

    <p>They influence rotational hindrance.</p> Signup and view all the answers

    Which organ primarily provides quick fuel needs for the body?

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

    Which statement correctly describes the function of aromatic amino acids?

    <p>They can be arranged to generate stacking forces.</p> Signup and view all the answers

    What role do hormones play in metabolism?

    <p>They are used to coordinate and regulate biochemical pathways.</p> Signup and view all the answers

    What effect do the properties of R groups have on peptide/protein stability?

    <p>They influence the rotational freedom of single bonds.</p> Signup and view all the answers

    In which manner do insulin and glucagon interact with metabolic pathways?

    <p>They differentially stimulate and inhibit specific pathways.</p> Signup and view all the answers

    What is the effect of hormonal signals on metabolic needs across various organs?

    <p>They ensure a steady supply of energy while allowing for energy storage.</p> Signup and view all the answers

    Which of these hormones is NOT typically involved in regulating metabolism?

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

    What are the main signals used in the integration of metabolism among organs?

    <p>Catecholamines, gluco-corticoids, and growth hormone</p> Signup and view all the answers

    What is one advantage of multienzyme complexes in metabolic pathways?

    <p>They prevent the loss or dilution of intermediates.</p> Signup and view all the answers

    How are enzymes for glycolysis and the citric acid cycle segregated in the cell?

    <p>Glycolysis takes place in the cytosol, while the citric acid cycle occurs in the mitochondria.</p> Signup and view all the answers

    What is a feature of membrane-bound enzyme systems?

    <p>Enzymes must diffuse only in two dimensions.</p> Signup and view all the answers

    Which compounds are classified as being in a more reduced state relative to others?

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

    What primarily drives biosynthetic reactions in living systems?

    <p>Oxidation of organic substrates.</p> Signup and view all the answers

    Why is the compartmentalization of metabolic pathways beneficial?

    <p>It facilitates the efficiency of biochemical reactions.</p> Signup and view all the answers

    Which statement best describes soluble multienzyme systems?

    <p>They function independently with diffusing intermediates.</p> Signup and view all the answers

    Where are most glycolytic enzymes located in the cell?

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

    Which of the following substances are classified as common nucleophiles in biochemical reactions?

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

    What is the primary consequence of atoms sharing or transferring valence electrons?

    <p>Chemical bonds are formed</p> Signup and view all the answers

    What is a key advantage of compartmentalizing metabolic pathways within specific organelles?

    <p>It prevents uncontrolled behavior of metabolic processes</p> Signup and view all the answers

    Which type of chemical bond is characterized by one atom stripping electrons from another?

    <p>Ionic bond</p> Signup and view all the answers

    Which statement accurately describes nucleophiles?

    <p>They are electron-rich and can form bonds with electrophiles.</p> Signup and view all the answers

    What is the role of chemical bonds in the formation of molecules?

    <p>They enable atoms to share or transfer electrons.</p> Signup and view all the answers

    Which of the following correctly describes a condition following the transfer of an electron between bonding partners?

    <p>Ions are formed with complete valence shells.</p> Signup and view all the answers

    What is one consequence of selective permeability of membranes in metabolic pathways?

    <p>Movement of metabolites can be efficiently controlled.</p> Signup and view all the answers

    Study Notes

    Tricarboxylic Acid (TCA) Cycle

    • The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a crucial part of cellular respiration.
    • It's a cyclical series of biochemical reactions that oxidizes the acetyl group from acetyl-CoA to carbon dioxide (CO2).
    • The cycle regenerates oxaloacetate, starting the cycle again.
    • It generates high-energy electron carriers (NADH and FADH2) and a small amount of ATP (GTP).
    • The TCA cycle is an amphibolic pathway, meaning it plays a role in both catabolic (breakdown) and anabolic (synthesis) processes.
    • Key enzymes in the cycle are: citrate synthase, aconitase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, and malate dehydrogenase.
    • The cycle takes place in the mitochondrial matrix.
    • Pyruvate dehydrogenase complex connects glycolysis and the TCA cycle by converting pyruvate to acetyl-CoA.
    • Anaplerotic reactions replenish TCA cycle intermediates like oxaloacetate.

    Energy Transformations in Fuel Metabolism

    • Phase 1 of respiration involves the oxidation of fuels (glucose, fatty acids, amino acids), transferring electrons.
    • Coenzymes NAD+ and FAD accept the transferred electrons, forming NADH and FAD(2H) respectively.
    • Phase 2 of respiration generates ATP through oxidative phosphorylation using the energy from the high-energy electron carriers (NADH and FAD(2H)).

    Overview of Glycolysis and Important Reactions

    • Glycolysis is an anaerobic process that converts glucose into pyruvate.
    • Important reactions like hexokinase, phosphofructokinase, and pyruvate kinase are involved in these conversions.
    • ATP is required in glycolysis, but a net gain of 2 ATP is yielded.
    • These reactions take place in the cytosol.

    Oxidative Fates of Pyruvate and Nicotinamide Adenine Dinucleotide

    • Aerobic glycolysis utilizes pyruvate to make Acetyl CoA to enter the TCA cycle.
    • Anaerobic glycolysis converts pyruvate into lactate.
    • Oxidation of organic compounds either involves loss of hydride ions (H−) or combining with oxygen.
    • Enzymes called dehydrogenases are responsible for these oxidation reactions.

    Anaerobic Conversion of Pyruvate to Ethanol

    • Yeast cells convert pyruvate to ethanol and CO2 in the absence of oxygen.
    • Two reactions are necessary. One being decarboxylation to pyruvate then to acetaldehyde, and the other being alcohol dehydrogenase reducing acetaldehyde to ethanol.
    • This process regenerates NAD+ from NADH allowing glycolysis to continue.

    The Citric Acid Cycle and What We Will Learn Today

    • The citric acid cycle (TCA cycle) is a cyclical process.
    • The cycle interconnects glycolysis and pyruvate dehydrogenase complex.
    • The cycle's reactions and the enzymes involved in the reactions.
    • Regulation of TCA cycle activity.
    • Anaplerotic reaction that replenishes TCA cycle intermediates.

    The Loci of Substrate-Level Phosphorylation

    • Substrate-level phosphorylation occurs in the cytosol during glycolysis and in the mitochondrion during the TCA cycle.
    • Electrons are transferred via NADH and FAD(2H) in these processes.

    Conversion of Pyruvate to Acetyl-CoA by Oxidative Decarboxylation

    • The conversion is carried out by the pyruvate dehydrogenase complex (PDC), a multi-enzyme complex.
    • The PDC requires five cofactors: TPP, lipoic acid, CoA, FAD, and NAD+.
    • The reaction takes place in the mitochondrial matrix.

    Acetyl-Coenzyme A (Acetyl-CoA)

    • Acetyl-CoA carries acetyl groups for metabolic processes.
    • It's a high-energy molecule that releases free energy for cellular reactions.
    • The common product of breakdown of carbohydrate, fatty acids, and amino acids.

    Comparison of Free Energies of Hydrolysis of Thioesters and Oxygen Esters

    • Thioesters are more favorable for hydrolysis than oxygen esters.
    • Lack of resonance stabilization in thioesters is why their hydrolysis is more favorable compared to oxygen esters.

    Conversion of Pyruvate to Acetyl-CoA by Oxidative Decarboxylation (Alternative)

    • Pyruvate Dehydrogenase Multienzyme Complex (PDC) catalyzes the conversion.
    • The PDC has three enzymes: E1 (pyruvate dehydrogenase), E2 (dihydrolipoyl transacetylase), and E3 (dihydrolipoyl dehydrogenase).
    • Five cofactors are needed: TPP, lipoic acid, CoASH, FAD, NAD+.
    • Occurs in the mitochondrial matrix.

    Structural Organization of the E. coli PDC

    • PDC is a multi-enzyme complex with a structure (E1, E2, E3) core. The structure is important to understand the mechanism in which they work together.

    The Coenzymes and Prosthetic Groups of PDC

    • Different coenzymes within the PDC facilitate different reaction steps, with TPP, lipoic acid, CoA (respectively E1, E2), and FAD & NAD+ (in E3) involved in specific parts and steps.
    • The roles of TPP and lipoic acid.
    • The role of CoA and FAD
    • The role of NAD+ within the complex.

    Interconversion of Lipoamide and Dihydrolipoamide

    • Lipoamide is a cofactor involved in the conversion of lipoic acid in the PDC complex, and crucial to the process.

    Thiamine Pyrophosphate (TPP)

    • TPP is a cofactor of pyruvate dehydrogenase complex.
    • It's involved in decarboxylation of pyruvate and transfer of a two-carbon unit.

    TPP in the Pyruvate Dehydrogenase Reaction

    • TPP plays a key role in the pyruvate dehydrogenase reaction, accepting the activated two-carbon unit of pyruvate, then transferring to an intermediate then to the next cofactor, CoA, which then becomes acetyl CoA.
    • The pyruvate dehydrogenase reaction, and each step is essential in order for the entire process to happen.

    Malfunction of Pyruvate Dehydrogenase Complex: TPP Deficiency

    • TPP deficiency inhibits pyruvate dehydrogenase complex activity.
    • Symptoms of TPP deficiency include neurological and cardiovascular disorders.
    • Deficiency can be diagnosed by testing the levels of pyruvate in the blood.

    TCA Cycle Provides a Way of Cleaving a Two-Carbon Compound

    • The TCA cycle provides a means to oxidize the acetyl group of acetate and convert to CO2, which requires C-C cleavage.
    • There is a chemical basis for the complexity of apparent oxidation of acetate units to carbon dioxide (CO2).

    The Concept of the TCA (Krebs) Cycle

    • The TCA cycle involves eight steps, each catalyzed by a specific enzyme.
    • The acetyl group from acetyl-CoA joins the cycle by combining with oxaloacetate to make citrate.
    • The cycle then regenerates oxaloacetate through the subsequent steps.
    • The NADH and FADH2 produced the cycle carry electron energy for electron transport chain.

    Formation of Succinyl-CoA (Alternative)

    • The process involves a series of redox reactions and decarboxylations ultimately creating Succinyl-CoA.

    Mechanism of the NAD+-Dependent Isocitrate Dehydrogenase

    • The reaction involves a series of redox steps leading to release of CO2 and the oxidation of an alcohol to form a keto-group.
    • The isocitrate dehydrogenase reaction uses Mn2+ (or Mg2+) to coordinate and facilitate the catalytic process.

    Mechanism of the NAD+-Dependent α-Ketoglutarate Dehydrogenase

    • This reaction catalyzes the oxidative decarboxylation of α-ketoglutarate to form succinyl-CoA using 5 cofactors: TPP, lipoic acid, CoASH, FAD&NAD+.

    Mechanism of the Succinyl-CoA Synthetase

    • The enzyme catalyzes substrate-level phosphorylation.
    • Succinyl-CoA is phosphorylated converting GTP to GDP, or ADP to ATP.
    • This is an essential process producing high-energy compounds.

    Reactions Catalyzed by Succinyl-CoA Synthetase

    • This enzyme catalyzes the formation and conversion of succinyl-phosphate, then a phosphoryl-His intermediate and finally product GTP through a series of intermediate steps, using GDP.

    Standard Free Energy Changes (ΔG') and Physiological Free Energy Changes (ΔG) of Citric Acid Cycle Reactions

    • The enzyme and reactions involved in each cycle step and their corresponding standard free energy changes values.
    • Standard and physiological free-energy changes for individual TCA cycle reactions.

    Major Regulatory Interactions in the TCA Cycle

    • The rate of ATP hydrolysis regulates the rate of NADH oxidation.
    • ADP and NADH provide feedback to control the TCA cycle.
    • Isocitrate dehydrogenase, α-ketoglutarate DH, and malate DH are affected by changes in NADH concentration.
    • Citrate inhibits citrate synthase.
    • ADP and Ca2+ concentration activates isocitrate and α-ketoglutarate DH.

    Factors Controlling the Activity of the PDC

    • Feedback of NADH and acetyl-CoA.
    • Production inhibition of a key reactant, pyruvate.

    Anaplerotic Pathways to Replenish TCA Cycle Intermediates

    • Anaplerotic reactions replenish TCA cycle intermediates.
    • Key reactions like pyruvate carboxylase and transamination.
    • The importance of these pathways.

    The TCA Cycle Provides Intermediates for Biosynthetic Processes

    • The TCA cycle provides building blocks for other metabolic processes and produces intermediates for biosynthesis.

    Quiz Questions (Information, not study notes)

    • Question 1: What is the ΔG°' value for hydrolysis of the thioester bond of Acetyl-CoA?
    • Question 2: What is the functional group in the thiazolium ring of TPP?
    • Question 3: How can the reduction of NAD+ spectroscopically be observed?
    • Question 4: Why is the Krebs cycle called Tricarboxyl Acid cycle (TCA)?
    • Question 5: Which enzyme/cofactor in the TCA cycle has a membrane connection? What cofactor does it use in catalysis?
    • Question 6: Which enzymes from the TCA cycle are likely to function far from equilibrium under physiological conditions?

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    Related Documents

    Metabolism Lecture 1 PDF
    Lecture 2- Glycolysis - Metabolic Fates of Pyruvate - PDF
    Lecture 3- TCA Cycle PDF

    Description

    Test your knowledge on the Tricarboxylic Acid (TCA) cycle, also known as the Krebs cycle. This quiz covers key components, processes, and enzymes involved in cellular respiration, including the regeneration of oxaloacetate and the role of electron carriers. Challenge your understanding of this essential metabolic pathway in biochemistry!

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