TCA Cycle and Encephalopathy Quiz

Questions and Answers

Which enzyme is specifically linked to the irreversible oxidative decarboxylation of isocitrate?

Lipoic acid synthase

Alpha-ketoglutarate dehydrogenase

Isocitrate dehydrogenase (correct)

Citrate synthase

What effect does an accumulation of pyruvate primarily have in the metabolic pathway discussed?

Increases production of ADP

Promotes the synthesis of ATP

Conversion to lactate (correct)

Enhances the function of isocitrate dehydrogenase

Which of the following is an inhibitor of the enzymes involved in the oxidation and decarboxylation of isocitrate?

FADH2

ADP

NADH (correct)

Coenzyme A

Which factor is known to activate the enzymes involved in the process of isocitrate oxidation?

ADP Signup and view all the answers

What is a potential consequence of inhibiting lipoic acid-dependent enzymes in the brain?

Neurologic disturbances and death Signup and view all the answers

Which enzyme is involved in the conversion of succinate to fumarate?

Succinate dehydrogenase Signup and view all the answers

What is the role of FAD in the oxidation of succinate?

It gets converted to FADH2. Signup and view all the answers

What is the significance of succinate dehydrogenase being embedded in the inner mitochondrial membrane?

It enables the enzyme to function as Complex II of the electron transport chain. Signup and view all the answers

Which compound is produced from the oxidative deamination or transamination of glutamate?

α-ketoglutarate Signup and view all the answers

What is the primary product formed when fumarate undergoes hydration?

L-Malate Signup and view all the answers

What is the most common consequence of pyruvate dehydrogenase deficiency?

Congenital Lactic Acidosis Signup and view all the answers

How does Fluoroacetate affect the TCA cycle?

Inhibits the conversion of citrate to isocitrate Signup and view all the answers

What is a potential treatment strategy for symptoms of pyruvate dehydrogenase deficiency?

Dietary restriction of carbohydrates Signup and view all the answers

Leigh syndrome is primarily associated with defects in which biochemical pathway?

Mitochondrial ATP Production Signup and view all the answers

What is the mechanism of arsenic poisoning in relation to the TCA cycle?

Forms a complex with lipoic acid Signup and view all the answers

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

Dehydration Signup and view all the answers

Which enzyme is inhibited by fluoroacetate, resulting in citrate accumulation?

Acotinase Signup and view all the answers

Which of the following conditions is a consequence of a mutation in the PDH complex?

Subacute necrotizing encephalomyelopathy Signup and view all the answers

What is the role of citrate in the TCA cycle?

Inhibits phosphofructokinase Signup and view all the answers

Which enzyme catalyzes the conversion of acetyl CoA and oxaloacetate to citrate?

Citrate synthase Signup and view all the answers

Which molecule is produced in the oxidative decarboxylation of α-ketoglutarate?

Succinyl CoA Signup and view all the answers

What coenzymes are required for the α-ketoglutarate dehydrogenase complex activity?

TPP, Lipoic acid, FAD, and NAD Signup and view all the answers

Which bond is cleaved during the synthesis of citrate?

High-energy thioester bond Signup and view all the answers

Which of the following is NOT a characteristic of citrate synthase?

It is an allosteric enzyme Signup and view all the answers

What is the relationship between GTP and ATP in the TCA cycle?

GTP can be converted to ATP with ADP Signup and view all the answers

What is the final product of the TCA cycle's conversion of carbon skeletons?

Carbon dioxide Signup and view all the answers

From where can succinyl CoA be produced?

From propionyl CoA and several amino acids Signup and view all the answers

Which of the following substances acts as an inhibitor of the pyruvate dehydrogenase complex?

NADH Signup and view all the answers

In which cellular organelle does the TCA cycle occur?

Mitochondria Signup and view all the answers

Which regulatory enzyme phosphorylates and inhibits the E1 component of the pyruvate dehydrogenase complex?

Pyruvate dehydrogenase kinase Signup and view all the answers

What major function does the TCA cycle serve in metabolism?

Final pathway for carbohydrate and fat metabolism Signup and view all the answers

Which compound serves as the final electron acceptor in the TCA cycle pathway?

Oxygen Signup and view all the answers

What biochemical consequence results from alcohol abuse related to TCA cycle function?

Thiamine deficiency and subsequent CNS problems Signup and view all the answers

Which activators indicate that the TCA cycle can proceed by activating the E1 component?

Acetyl CoA and calcium Signup and view all the answers

What condition occurs when brain cells fail to produce enough ATP due to inactive PDH complex?

Encephalopathy-psychosis syndrome Signup and view all the answers

How does the TCA cycle relate to the reactions of the electron transport chain?

They occur in close proximity, facilitating oxidation processes Signup and view all the answers

Study Notes

Overview of the TCA Cycle

Also known as Kreb’s cycle or Citric acid cycle.
Final metabolic pathway merging carbohydrate, amino acids, and fatty acids metabolism.
Converts carbon skeletons to CO2 and produces the majority of ATP.
Occurs in mitochondria, closely linked to electron transport reactions.
Functions as an aerobic pathway utilizing O2 as the final electron acceptor.

Regulation of the TCA Cycle

Pyruvate Dehydrogenase (PDH) complex is crucial for TCA cycle regulation.
PDH complex activation/inhibition occurs through specific enzymes.
Pyruvate dehydrogenase kinase: Phosphorylates/inhibits E1 (PDH complex), deactivating the cycle; activated by ATP, acetyl CoA, NADH; inhibited by pyruvate.
Pyruvate dehydrogenase phosphatase: Dephosphorylates/activates E1, allowing the cycle to proceed; activated by calcium, enhancing energy production during muscle contraction.

TCA Cycle Reactions

Oxidative Decarboxylation of Pyruvate: Pyruvate acts as an end product of aerobic glycolysis, requiring a specific transporter for entry into the cycle.
Isomerization of Citrate: Citrate converts to isocitrate via aconitase, inhibited by fluoroacetate, leading to citrate accumulation.
Pyruvate Dehydrogenase Deficiency: Main cause of Congenital Lactic Acidosis, an X-linked dominant disorder, causing neurodegeneration, muscle spasticity, and neonatal death; dietary interventions may alleviate symptoms.
Leigh Syndrome: Caused by mutations in PDH complex or ATP synthase, leading to subacute necrotizing encephalomyelopathy and progressive neurological deficits.

Specific Steps in TCA Cycle

Synthesis of Citrate: Acetyl CoA + Oxaloacetate forms citrate, catalyzed by citrate synthase; citrate inhibits citrate synthase and phosphofructokinase while activating acetyl CoA carboxylase.
Oxidative Decarboxylation of α-Ketoglutarate: α-Ketoglutarate converted to succinyl CoA, yielding 2 CO2 and NADH with coenzymes TPP, lipoic acid, FAD, NAD, and CoA required.
Oxidation of Succinate: Succinate converts to fumarate via succinate dehydrogenase, which embeds in the inner mitochondrial membrane, functioning also as Complex II of the electron transport chain.
Hydration of Fumarate: Fumarase catalyzes the conversion of fumarate to L-malate, linking to various metabolic pathways including the urea cycle.

Mechanism of Toxicity

Arsenic Poisoning: Binds to thiol groups of lipoic acid, impairing enzymatic activity requiring lipoic acid as a coenzyme, leading to pyruvate accumulation and lactate production, affecting neurological functions.

Encephalopathy-Psychosis Syndrome: Associated with disruptions in TCA cycle function, potentially from vitamin deficiencies or substance abuse.
CNS Problems: Brain cells fail to produce adequate ATP when the PDH complex is inactive, underlying neurodevelopmental issues.

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Description

Test your knowledge on the energy production of the TCA cycle and its regulation. This quiz covers the impact of conditions such as thiamine deficiency and alcohol abuse on the central nervous system. Dive into the complexities of metabolic disorders.