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Questions and Answers
What is the main product of the reaction catalyzed by the pyruvate dehydrogenase complex?
What is the main product of the reaction catalyzed by the pyruvate dehydrogenase complex?
- Hydroxyethyl-TPP
- Acetyl-CoA (correct)
- Lipoamide
- NADH
Which enzyme in the PDH complex is responsible for regenerating the oxidized form of lipoamide?
Which enzyme in the PDH complex is responsible for regenerating the oxidized form of lipoamide?
- Acetyl-CoA synthase
- Dihydrolipoyl transacetylase (E2)
- Dihydrolipoyl dehydrogenase (E3) (correct)
- Pyruvate dehydrogenase (E1)
Which of the following molecules would act as an allosteric inhibitor of the PDH complex?
Which of the following molecules would act as an allosteric inhibitor of the PDH complex?
- NAD+
- Pyruvate
- Acetyl-CoA (correct)
- ADP
What regulatory mechanism is employed by the PDH complex to inhibit its activity?
What regulatory mechanism is employed by the PDH complex to inhibit its activity?
Why is the PDH complex critical for energy production in cells?
Why is the PDH complex critical for energy production in cells?
Which component of the PDH complex directly transfers the acetyl group to lipoamide?
Which component of the PDH complex directly transfers the acetyl group to lipoamide?
Which of the following statements is true regarding the role of acetyl-CoA in metabolism?
Which of the following statements is true regarding the role of acetyl-CoA in metabolism?
What is the role of PDH phosphatase in the regulation of the PDH complex?
What is the role of PDH phosphatase in the regulation of the PDH complex?
Which enzyme in the PDH complex is responsible for the formation of a hydroxyethyl-TPP intermediate?
Which enzyme in the PDH complex is responsible for the formation of a hydroxyethyl-TPP intermediate?
Which factor acts as an allosteric activator of PDH activity?
Which factor acts as an allosteric activator of PDH activity?
Which enzyme of the PDH complex is responsible for converting pyruvate into a hydroxyethyl-TPP intermediate?
Which enzyme of the PDH complex is responsible for converting pyruvate into a hydroxyethyl-TPP intermediate?
What is the main product of the reaction catalyzed by the PDH complex?
What is the main product of the reaction catalyzed by the PDH complex?
Which of the following does NOT inhibit PDH activity?
Which of the following does NOT inhibit PDH activity?
What is the effect of acetyl-CoA on the activity of the PDH complex?
What is the effect of acetyl-CoA on the activity of the PDH complex?
Which of the following statements about the TCA cycle is correct?
Which of the following statements about the TCA cycle is correct?
What is the function of dihydrolipoyl dehydrogenase (E3) in the PDH complex?
What is the function of dihydrolipoyl dehydrogenase (E3) in the PDH complex?
What is produced when the PDH complex regenerates the oxidized form of lipoamide?
What is produced when the PDH complex regenerates the oxidized form of lipoamide?
How does PDH regulation help balance cellular energy production?
How does PDH regulation help balance cellular energy production?
Which of the following factors does not lead to the activation of the PDH complex?
Which of the following factors does not lead to the activation of the PDH complex?
Acetyl-CoA is a key precursor in which of the following metabolic processes?
Acetyl-CoA is a key precursor in which of the following metabolic processes?
What role does the PDH complex play in metabolic regulation?
What role does the PDH complex play in metabolic regulation?
What is the significance of the PDH complex in relation to the citric acid cycle?
What is the significance of the PDH complex in relation to the citric acid cycle?
Which statement about the components of the PDH complex is incorrect?
Which statement about the components of the PDH complex is incorrect?
What is the main function of acetyl-CoA in metabolism?
What is the main function of acetyl-CoA in metabolism?
What is the primary molecule that acetyl-CoA combines with to enter the TCA cycle?
What is the primary molecule that acetyl-CoA combines with to enter the TCA cycle?
Which molecule is produced alongside CO2 during the conversion of isocitrate to α-ketoglutarate?
Which molecule is produced alongside CO2 during the conversion of isocitrate to α-ketoglutarate?
What type of phosphorylation occurs during the conversion of succinyl-CoA to succinate?
What type of phosphorylation occurs during the conversion of succinyl-CoA to succinate?
Which intermediates of the TCA cycle serve as precursors for amino acid biosynthesis?
Which intermediates of the TCA cycle serve as precursors for amino acid biosynthesis?
Which energy molecules are produced during one turn of the TCA cycle?
Which energy molecules are produced during one turn of the TCA cycle?
How is the activity of the TCA cycle regulated?
How is the activity of the TCA cycle regulated?
What role does the TCA cycle play in catabolism?
What role does the TCA cycle play in catabolism?
What molecule is generated from fumarate during its conversion to malate?
What molecule is generated from fumarate during its conversion to malate?
Which molecule combines with acetyl-CoA to initiate the TCA cycle?
Which molecule combines with acetyl-CoA to initiate the TCA cycle?
Which step in the TCA cycle produces both NADH and CO2?
Which step in the TCA cycle produces both NADH and CO2?
What type of phosphorylation occurs during the conversion of succinyl-CoA to succinate?
What type of phosphorylation occurs during the conversion of succinyl-CoA to succinate?
How many molecules of NADH are produced in one turn of the TCA cycle?
How many molecules of NADH are produced in one turn of the TCA cycle?
Which of the following statements accurately describes the role of intermediates in the TCA cycle?
Which of the following statements accurately describes the role of intermediates in the TCA cycle?
What is the final product of the TCA cycle that regenerates to complete the cycle?
What is the final product of the TCA cycle that regenerates to complete the cycle?
Which factor does NOT directly regulate the activity of the TCA cycle?
Which factor does NOT directly regulate the activity of the TCA cycle?
Which cellular location is associated with the TCA cycle in eukaryotic cells?
Which cellular location is associated with the TCA cycle in eukaryotic cells?
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Study Notes
Pyruvate Dehydrogenase (PDH) Overview
- Pyruvate dehydrogenase (PDH) converts pyruvate from glycolysis into acetyl-CoA, linking glycolysis with the citric acid cycle.
- This reaction is essential for ATP production via aerobic respiration.
Components of PDH Complex
- E1: Pyruvate Dehydrogenase
- Catalyzes decarboxylation of pyruvate, forming a hydroxyethyl-TPP intermediate.
- E2: Dihydrolipoyl Transacetylase
- Transfers the acetyl group from hydroxyethyl-TPP to lipoamide, producing acetyl-CoA.
- E3: Dihydrolipoyl Dehydrogenase
- Regenerates oxidized lipoamide, producing NADH.
Regulation of PDH Activity
- Phosphorylation
- PDH kinase inhibits PDH by adding phosphate groups.
- PDH phosphatase activates PDH by removing phosphate groups.
- Allosteric Regulation
- Inhibitors: Acetyl-CoA, NADH, and ATP.
- Activators: Pyruvate and ADP.
Significance of PDH in Metabolism
- Energy Production
- Converts pyruvate to acetyl-CoA, fueling the citric acid cycle and ATP generation via oxidative phosphorylation.
- Metabolic Regulation
- Balances energy production with cellular energy demands.
- Anabolism
- Acetyl-CoA serves as a precursor for fatty acid synthesis and other anabolic pathways.
Citric Acid Cycle (TCA Cycle) Overview
- The TCA cycle, also known as the Krebs cycle, is crucial for energy production through aerobic respiration.
- Occurs in the mitochondrial matrix of eukaryotes and the cytoplasm of prokaryotes.
Key Steps of the TCA Cycle
- Entry of Acetyl-CoA
- Acetyl-CoA combines with oxaloacetate to form citrate.
- Citrate to Isocitrate
- Isomerization of citrate produces isocitrate.
- Isocitrate to α-Ketoglutarate
- Oxidation and decarboxylation of isocitrate yield α-ketoglutarate, CO2, and NADH.
- α-Ketoglutarate to Succinyl-CoA
- Oxidative decarboxylation yields succinyl-CoA, CO2, and NADH.
- Succinyl-CoA to Succinate
- Conversion coupled with substrate-level phosphorylation, producing GTP.
- Succinate to Fumarate
- Succinate oxidation forms fumarate and FADH2.
- Fumarate to Malate
- Fumarate undergoes hydration to yield malate.
- Malate to Oxaloacetate
- Malate oxidation regenerates oxaloacetate and produces NADH, completing the cycle.
Energy Production from the TCA Cycle
- Each turn produces:
- 1 ATP (or GTP) through substrate-level phosphorylation.
- 3 NADH.
- 1 FADH2.
- These energy carriers feed into the electron transport chain for ATP generation through oxidative phosphorylation.
Importance of the TCA Cycle
- Energy Production
- Vital for generating ATP, the main energy currency in cells.
- Anabolism
- Intermediates are precursors for amino acid and fatty acid synthesis.
- Catabolism
- Involved in the breakdown of amino acids and fatty acids.
- Regulation
- Activity is influenced by substrate availability, cellular energy needs, and allosteric factors like ATP and NADH.
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