Kreb's Cycle Flashcards by Mind Med

What does a high NADH/NAD+ ratio indicate?

A. Increased oxidation capacity
B. Increased need for ATP production
C. High energy status, slowing TCA cycle
D. Activation of dehydrogenases

C. High energy status, slowing TCA cycle

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What is the net ATP yield in the complete oxidation of 1mole of glucose to CO2 and water in the liver?
A. 10
B. 20
C. 30
D. 32

D. 32

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How many ATPs are synthesized in the muscles via glycolysis, PDH and TCA cycle?

Only 30 because glycolysis lacks 2 ATP dt usage of FADH not NADH

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Which step of the TCA cycle produces GTP by substrate-level phosphorylation?

A. Isocitrate → α-ketoglutarate
B. α-Ketoglutarate → Succinyl-CoA
C. Succinyl-CoA → Succinate
D. Malate → Oxaloacetate

C. Succinyl-CoA → Succinate

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If you were to design a drug to slow down the TCA cycle for cancer therapy, which enzyme would be the best target?

A. Succinate thiokinase
B. Malate dehydrogenase
C. Isocitrate dehydrogenase
D. Fumarase

C. Isocitrate dehydrogenase

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Which enzyme of the TCA cycle is also part of the electron transport chain (Complex II)?

A. Citrate synthase
B. Succinate dehydrogenase
C. Aconitase
D. Malate dehydrogenase

B. Succinate dehydrogenase

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Why does inhibition of aconitase by fluorocitrate cause citrate to accumulate?

A. Citrate synthase activity increases
B. Citrate cannot be isomerized to isocitrate
C. Succinate dehydrogenase is inhibited
D. NADH levels rise, blocking citrate breakdown

B. Citrate cannot be isomerized to isocitrate

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Which cofactor is NOT required by the α-ketoglutarate dehydrogenase complex?

A. Thiamine pyrophosphate (TPP)
B. Lipoic acid
C. FAD
D. Biotin

D. Biotin

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A patient with thiamine deficiency will have impaired activity of which TCA enzyme?

A. Succinate dehydrogenase
B. Isocitrate dehydrogenase
C. α-Ketoglutarate dehydrogenase
D. Malate dehydrogenase

C. α-Ketoglutarate dehydrogenase

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Why is the Citric Acid Cycle considered amphibolic?

A. produces only energy
B. helps synthesize ATP only during fasting
C. functions in both breakdown & synthesis of molecules
D. requires only acetyl-CoA as input

C. functions in both breakdown & synthesis of molecules

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Why does high NADH/NAD⁺ ratio inhibit PDH activity?

A. It increases CoA availability
B. It signals high energy status, activating PDH kinase
C. It enhances Ca²⁺ binding to PDH phosphatase
D. It promotes thiamine pyrophosphate formation

B. It signals high energy status, activating PDH kinase

Increase in energy stops production

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Which of the following best explains why arsenic poisoning inhibits PDC activity?

A. Arsenic binds irreversibly to the FAD-binding site in E3
B. Arsenic binds to sulfhydryl groups in lipoic acid, preventing acetyl transfer
C. Arsenic competes with NAD⁺ for binding to E3
D. Arsenic directly decarboxylates pyruvate, bypassing PDC

B. Arsenic binds to sulfhydryl groups in lipoic acid, preventing acetyl transfer

Arsenide has a high affinity to sulfhydryl groups

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A patient presents with neurological symptoms due to a thiamine deficiency. Which step of the PDC function will be directly impaired?

A. Acetyl group transfer from lipoic acid to CoA
B. Oxidation of dihydrolipoamide by FAD
C. Decarboxylation of pyruvate
D. Electron transfer from NADH to the ETC

C. Decarboxylation of pyruvate

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Which cofactor is bound to the E1 subunit of the pyruvate dehydrogenase complex?

A. Lipoic acid
B. FAD
C. Thiamine pyrophosphate (TPP)
D. Coenzyme A

C. Thiamine pyrophosphate (TPP)

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Which of the following statements is TRUE of PDH reaction?

A. It produces glucose from pyruvate
B. It converts acetyl-CoA into pyruvate
C. It converts pyruvate into acetyl-CoA
D. It regenerates NAD⁺ for glycolysis

C. It converts pyruvate into acetyl-CoA

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Which enzyme in the PDH complex is responsible for the decarboxylation of pyruvate?
a) Dihydrolipoyl transacetylase (E2)
b) Pyruvate dehydrogenase (E1)
c) Dihydrolipoyl dehydrogenase (E3)
d) Citrate synthase

b) Pyruvate dehydrogenase (E1)

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What is the coenzyme required by the Pyruvate dehydrogenase (E1) enzyme for decarboxylation?
a) Lipoic acid
b) Coenzyme A
c) Thiamine pyrophosphate (TPP)
d) NAD+

c) Thiamine pyrophosphate (TPP)

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In the PDH complex, what is the direct carrier of the two-carbon acetyl group before it is transferred to Coenzyme A?
a) Oxidized lipoamide
b) Acetyl lipoamide
c) Hydroxyethyl TPP
d) NADH

b) Acetyl lipoamide

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What cofactor is required for the regeneration of oxidized lipoamide by dihydrolipoyl dehydrogenase (E3)?
a) NAD+ and FAD
b) TPP and CoA
c) ATP and ADP
d) NADH and FADH2

a) NAD+ and FAD

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Which molecule is the final product of the PDH complex that enters the TCA cycle?
a) Pyruvate
b) Acetyl-CoA
c) Citrate
d) Succinyl-CoA

b) Acetyl-CoA

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What are the five cofactors of the PDH complex?
a) ATP, NADH, FAD, CoA, Biotin
b) TPP, Lipoic acid, CoA, FAD, NAD+
c) NAD+, FAD, Biotin, ATP, CoA
d) TPP, CoA, ATP, NADH, Lipoic acid

b) TPP, Lipoic acid, CoA, FAD, NAD+

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Which step of the PDH complex reaction produces CO2?
a) Transfer of acetyl group to CoA
b) Reoxidation of lipoamide
c) Decarboxylation of pyruvate to hydroxyethyl TPP
d) Conversion of NAD+ to NADH

c) Decarboxylation of pyruvate to hydroxyethyl TPP

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How is the PDH complex regulated by phosphorylation?
a) Phosphorylation activates PDH complex
b) Phosphorylation inhibits PDH complex by PDH kinase
c) Dephosphorylation inhibits PDH complex
d) It is not regulated by phosphorylation

b) Phosphorylation inhibits PDH complex by PDH kinase

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What allosteric effectors activate PDH kinase leading to PDH complex inhibition?
a) ADP and pyruvate
b) Acetyl-CoA, NADH, and ATP
c) Calcium ions
d) Insulin and catecholamines

b) Acetyl-CoA, NADH, and ATP

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Which enzyme in PDH complex uses NAD+ as an oxidizing agent to regenerate its prosthetic group? a) Pyruvate dehydrogenase (E1) b) Dihydrolipoyl transacetylase (E2) c) Dihydrolipoyl dehydrogenase (E3) d) Citrate synthase

c) Dihydrolipoyl dehydrogenase (E3)

What is the first substrate that condenses with acetyl-CoA to start the TCA cycle? a) Malate b) Citrate c) Oxaloacetate d) Succinyl-CoA

c) Oxaloacetate

Which enzyme catalyzes the conversion of citrate to isocitrate? a) Aconitase b) Citrate synthase c) Isocitrate dehydrogenase d) Succinate dehydrogenase

a) Aconitase

Which reaction in the TCA cycle is considered the rate-limiting step? a) Citrate to isocitrate b) Isocitrate to α-ketoglutarate c) α-Ketoglutarate to succinyl-CoA d) Succinyl-CoA to succinate

b) Isocitrate to α-ketoglutarate

How many NADH molecules are produced in one turn of the TCA cycle? a) 1 b) 2 c) 3 d) 4

c) 3

Which TCA cycle enzyme also participates directly in the electron transport chain? a) Succinate dehydrogenase b) Malate dehydrogenase c) Aconitase d) Citrate synthase

a) Succinate dehydrogenase

Which reaction in the TCA cycle produces GTP (or ATP) via substrate-level phosphorylation? a) Isocitrate to α-ketoglutarate b) Succinyl-CoA to succinate c) Malate to oxaloacetate d) Citrate to isocitrate

b) Succinyl-CoA to succinate

Which TCA cycle reactions release CO2? a) Citrate to isocitrate & Malate to oxaloacetate b) Isocitrate to α-ketoglutarate & α-ketoglutarate to succinyl-CoA c) Succinate to fumarate & Fumarate to malate d) Succinyl-CoA to succinate & Malate to oxaloacetate

b) Isocitrate to α-ketoglutarate & α-ketoglutarate to succinyl-CoA

Which coenzyme is required for the oxidative decarboxylation reactions catalyzed by the α-ketoglutarate dehydrogenase complex? a) NADP+ b) FAD c) TPP d) Biotin

c) TPP

What is the net ATP yield (approximately) from one turn of the TCA cycle including NADH and FADH2 oxidation? a) 5 ATP b) 10 ATP c) 15 ATP d) 20 ATP

b) 10 ATP

Which enzymes catalyze irreversible reactions in the TCA cycle? a) Citrate synthase, malate dehydrogenase, fumarase b) Aconitase, succinate dehydrogenase, isocitrate dehydrogenase c) Citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase d) Succinyl-CoA synthetase, malate dehydrogenase, aconitase

c) Citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase

Which TCA cycle enzyme is inhibited by fluoroacetate poisoning? a) Succinate dehydrogenase b) Aconitase c) Citrate synthase d) Isocitrate dehydrogenase

b) Aconitase

In one turn of the TCA cycle, how many molecules of CO2 are released? a) 1 b) 2 c) 3 d) 4

b) 2

What are the products of the oxidation of succinate to fumarate? a) NADH + H+ b) FADH2 c) ATP d) CO2

b) FADH2

Which cofactor associated with the TCA cycle is part of Coenzyme A? a) Pantothenic acid (Vitamin B5) b) Thiamine (Vitamin B1) c) Niacin (Vitamin B3) d) Riboflavin (Vitamin B2)

a) Pantothenic acid (Vitamin B5)

What type of reaction is catalyzed by succinyl-CoA synthetase? a) Oxidative decarboxylation b) Substrate-level phosphorylation c) Hydration d) Isomerization

b) Substrate-level phosphorylation

What is a major consequence of inherited pyruvate dehydrogenase deficiency? a) Increased acetyl-CoA production b) Lactic acidosis and neurological symptoms c) Excessive ATP production d) Hyperglycemia

b) Lactic acidosis and neurological symptoms

Wernicke encephalopathy results from a deficiency of which vitamin essential for PDH complex activity? a) Vitamin B2 (Riboflavin) b) Vitamin B3 (Niacin) c) Vitamin B1 (Thiamine) d) Vitamin B5 (Pantothenic acid)

c) Vitamin B1 (Thiamine)

What effect does thiamine deficiency have on glucose metabolism? a) Increased glycolysis b) Blockade of PDH causing impaired ATP production c) Increased gluconeogenesis d) Enhanced TCA cycle activity

b) Blockade of PDH causing impaired ATP production

In arsenic poisoning, which TCA cycle enzyme complex is inhibited, causing accumulation of the substrate? a) Citrate synthase b) α-Ketoglutarate dehydrogenase complex c) Succinate dehydrogenase d) Malate dehydrogenase

b) α-Ketoglutarate dehydrogenase complex

How does excess NADH affect the regulation of the PDH complex? a) Activates PDH phosphatase b) Activates PDH kinase leading to inhibition of PDH c) Inhibits PDH kinase d) No effect on PDH complex

b) Activates PDH kinase leading to inhibition of PDH

Which condition is characterized by decreased activity of PDH and results in neurological symptoms due to poor ATP production in the brain? a) Diabetes mellitus b) Wernicke encephalopathy c) Inherited PDH deficiency d) Ethanol-induced hypoglycemia

c) Inherited PDH deficiency

Increased levels of which metabolite stimulate the PDH kinase to phosphorylate and inhibit the PDH complex? a) Pyruvate b) ADP c) Acetyl-CoA d) Calcium ions

c) Acetyl-CoA

During intense muscular contraction, which ion increases and activates PDH phosphatase? a) Sodium b) Calcium c) Potassium d) Chloride

b) Calcium

In cases of lactic acidosis resulting from PDH deficiency, which metabolic pathway is upregulated due to pyruvate accumulation? a) Glycolysis b) Gluconeogenesis c) Lactate production via lactate dehydrogenase d) Fatty acid oxidation

c) Lactate production via lactate dehydrogenase

Korsakoff syndrome is caused by a combination of thiamine deficiency and excessive intake of what substance? a) Nicotinic acid b) Alcohol c) Glucose d) Acetyl-CoA

b) Alcohol

Which cofactor associated with the TCA cycle is part of Complex 3? a) Pantothenic acid (Vitamin B5) b) Thiamine (Vitamin B1) c) Niacin (Vitamin B3) d) Riboflavin (Vitamin B2) Tip! You may select more than 1 answer

C & D

Which cofactor associated with the TCA cycle is part of Complex 1? a) Pantothenic acid (Vitamin B5) b) Thiamine (Vitamin B1) c) Niacin (Vitamin B3) d) Riboflavin (Vitamin B2) Tip! You may select more than 1 answer

b) Thiamine (Vitamin B1)

Which enzyme in PDH complex uses is used in Complex II of the PDH Complex? a) Pyruvate dehydrogenase b) Dihydrolipoyl transacetylase c) Dihydrolipoyl dehydrogenase d) Citrate synthase

b) Dihydrolipoyl transacetylase

How many ATP is produced with 1 FADH molecule?

1.5

How many ATP is produced with 1 NADH molecule?

2.5

How many ATP is produced by the PDH complex with 1 glucose?

5 ATP 1 glucose = 2 pyruvates 1 pyruvate = 1 NADH = 2.5 ATP

This pathway is responsible to convert pyruvate to OAA

PDH Complex

PDH Complex A. Anabolic B. Catabolic

A. Anabolic

activated by phosphorylation A. Anabolic enzyme B. Catabolic enzyme

B. Catabolic enzyme

activated by dephosphorylation A. Anabolic enzyme B. Catabolic enzyme

A. Anabolic enzyme

This type of regulation depends on number of enzymes produced in fed or fasting conditions A. Transcriptional modification B. Allosteric modification C. Covalent modification

A. Transcriptional modification

This pathway acts as a bridge between CHO pathways and TCA cycle

PDH Complex

TRUE OR FALSE: PDH Complex is an irreversible pathway

True

Pyruvate is transported to the mitochondria via?

Proton symporter

Which pathway accounts for 2/3 or more than half of the ATP produced in the body? A. ETC B. Kreb's Cycle C. Gluconeogenesis D. Glycolysis

B. Kreb's Cycle

TRUE OR FALSE: Kreb's Cycle is an aerobic pathway

True it requires oxygen as the final acceptor

Which substrate in the TCA cycle is regenerated?

OAA

What is the second oxidative decarboxylation? A. alpha-ketoglutarate > succinyl-CoA B. succinyl CoA > succinate C. fumarate > malate

A. alpha-ketoglutarate > succinyl-CoA

Enumerate the TCA Substrates and Intermediates

OAA > Citrate > Isocitrate > alpha-Ketoglutarate > Succinyl CoA > Succinate > Fumarate > Malate Mnemonic: Our City Is Kept Safe & Sound From Monsters

Which 2 substates form Citrate?

Acetyl-CoA and OAA

Fluroacetate inhibits what enzyme?

Aconitase This leads to build up of citrate

What is the first oxidative decarboxylation? A. isocitrate > alpha-ketoglutarate B. succinyl CoA > succinate > C. fumarate > malate

A. isocitrate > alpha-ketoglutarate this is also its RATE LIMITNG STEP

this is the only enzyme to participate in both ETC and TCA

succinate dehydrogenase also known as succinate coenzyme Q reductase or enzyme complex II

this is the only enzymes seen in the intramitochondrial space

succinate dehydrogenase and aconitase all other are found in the matrix

which reaction in the TCA leads to FADH production?

succinate to fumarate

which reaction in the TCA is related to the ETC enzymes?

succinate to fumarate uses succinate DH

On a complete TCA cycle, how many total ATP is produced from 2 Acetly-CoA?

20 ATP

In 1 TCA cycle, how many ATP is produced from 2 pyruvates?

10 ATP 7.5 from NADH 1.5 from FADH 1 from substrate level phosphorylation

On a complete TCA cycle, how many total NADH & FADH is produced from 1 Acetyl-CoA?

3 NADH 1 FADH

This refers to metabolic process that fill up or replenish intermediates of a metabolic pathways, most seen in TCA

Anaplerotic

Glutamate and glutamine yields what intermediate in the TCA

Alpha-ketoglutarate

What happens to acetyl coa to be able to move from the mitochondria to the cytosol

Becomes citrate to cross then uses citrate lyase to split into oaa and acetyl coa Acetyl-CoA is the used for fatty acid synthesis

Kreb's Cycle Flashcards

(82 cards)