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Questions and Answers
What is the primary role of the citric acid cycle in cellular metabolism?
What is the primary role of the citric acid cycle in cellular metabolism?
- Facilitating energy production and biosynthesis (correct)
- Breaking down fatty acids for energy
- Producing glucose from fatty acids
- Regulating blood sugar levels
Which molecule is formed by the reaction of oxaloacetate and Acetyl-CoA?
Which molecule is formed by the reaction of oxaloacetate and Acetyl-CoA?
- Isocitrate
- Succinate
- Cis-aconitate
- Citrate (correct)
Where do the enzymatic reactions of the citric acid cycle take place?
Where do the enzymatic reactions of the citric acid cycle take place?
- On the surface of the cell membrane
- In the cytoplasm of the cell
- In the nucleus of the cell
- In the matrix of the mitochondria (correct)
What is released during the formation of citrate from Acetyl-CoA and oxaloacetate?
What is released during the formation of citrate from Acetyl-CoA and oxaloacetate?
Which enzyme mediates the isomerization of citrate to isocitrate?
Which enzyme mediates the isomerization of citrate to isocitrate?
What intermediate is formed during the isomerization of citrate to isocitrate?
What intermediate is formed during the isomerization of citrate to isocitrate?
Which of the following statements is true regarding the citric acid cycle?
Which of the following statements is true regarding the citric acid cycle?
Which stage of cellular metabolism immediately follows the citric acid cycle?
Which stage of cellular metabolism immediately follows the citric acid cycle?
What is the starting molecule for the Kreb Cycle?
What is the starting molecule for the Kreb Cycle?
How many reactions are there in the Kreb Cycle?
How many reactions are there in the Kreb Cycle?
What happens to the acetyl group during the Kreb Cycle?
What happens to the acetyl group during the Kreb Cycle?
What is the primary function of the Succinyl-CoA synthetase?
What is the primary function of the Succinyl-CoA synthetase?
Which atom in oxaloacetate is released as carbon dioxide during the cycle?
Which atom in oxaloacetate is released as carbon dioxide during the cycle?
What process regenerates the same metabolite at the end of the Kreb Cycle?
What process regenerates the same metabolite at the end of the Kreb Cycle?
Which cofactor is released during the action of Succinyl-CoA synthetase?
Which cofactor is released during the action of Succinyl-CoA synthetase?
What role does the lipoamide cofactor play in the E2 complex?
What role does the lipoamide cofactor play in the E2 complex?
Which enzyme is primarily involved in the first step of the Kreb Cycle?
Which enzyme is primarily involved in the first step of the Kreb Cycle?
In addition to a small molecule starting point, what type of group does the Kreb Cycle incorporate?
In addition to a small molecule starting point, what type of group does the Kreb Cycle incorporate?
What product is formed when succinate is oxidized by succinate dehydrogenase?
What product is formed when succinate is oxidized by succinate dehydrogenase?
Where is succinate dehydrogenase located?
Where is succinate dehydrogenase located?
What is the end product of the Kreb Cycle that can be reused to begin another cycle?
What is the end product of the Kreb Cycle that can be reused to begin another cycle?
What happens to the hydrogen atoms extracted from succinate during its oxidation?
What happens to the hydrogen atoms extracted from succinate during its oxidation?
In addition to its role in the citric acid cycle, what is another function of succinate dehydrogenase?
In addition to its role in the citric acid cycle, what is another function of succinate dehydrogenase?
What is the equivalent energy currency produced by Succinyl-CoA synthetase?
What is the equivalent energy currency produced by Succinyl-CoA synthetase?
What is the primary function of the alpha-ketoglutarate dehydrogenase (KGDH) enzyme?
What is the primary function of the alpha-ketoglutarate dehydrogenase (KGDH) enzyme?
Which cofactor is NOT used by the alpha-ketoglutarate dehydrogenase?
Which cofactor is NOT used by the alpha-ketoglutarate dehydrogenase?
In the mechanism of KGDH, which component attacks the carbonyl carbon of alpha-ketoglutarate?
In the mechanism of KGDH, which component attacks the carbonyl carbon of alpha-ketoglutarate?
What structural change occurs at the C2 position during the reaction catalyzed by KGDH?
What structural change occurs at the C2 position during the reaction catalyzed by KGDH?
What molecules are produced during the reaction catalyzed by isocitrate dehydrogenase?
What molecules are produced during the reaction catalyzed by isocitrate dehydrogenase?
How does KGDH's mechanism compare to that of the pyruvate dehydrogenase (PDH) complex?
How does KGDH's mechanism compare to that of the pyruvate dehydrogenase (PDH) complex?
Which cofactor is NOT utilized by isocitrate dehydrogenase during its reaction?
Which cofactor is NOT utilized by isocitrate dehydrogenase during its reaction?
What role does lipoamide play in the KGDH reaction?
What role does lipoamide play in the KGDH reaction?
What role does NAD+ play in the reaction mechanism of isocitrate dehydrogenase?
What role does NAD+ play in the reaction mechanism of isocitrate dehydrogenase?
What is produced alongside Succinyl-CoA during the KGDH catalytic process?
What is produced alongside Succinyl-CoA during the KGDH catalytic process?
What is the primary function of the acidic residue in the active site of isocitrate dehydrogenase?
What is the primary function of the acidic residue in the active site of isocitrate dehydrogenase?
In the second step of the reaction, which type of activity does isocitrate dehydrogenase primarily perform?
In the second step of the reaction, which type of activity does isocitrate dehydrogenase primarily perform?
Which substrate is directly involved in the mechanism of KGDH?
Which substrate is directly involved in the mechanism of KGDH?
What product is formed as an intermediate during the decarboxylation step of the reaction?
What product is formed as an intermediate during the decarboxylation step of the reaction?
How does Mg2+ contribute to the function of isocitrate dehydrogenase?
How does Mg2+ contribute to the function of isocitrate dehydrogenase?
Why is isocitrate dehydrogenase named specifically for its oxidation role?
Why is isocitrate dehydrogenase named specifically for its oxidation role?
What is the primary function of fumarase in the Kreb cycle?
What is the primary function of fumarase in the Kreb cycle?
Which product is formed in the final reaction of the citric acid cycle?
Which product is formed in the final reaction of the citric acid cycle?
How many molecules of NADH & H+ are produced per cycle of the citric acid cycle?
How many molecules of NADH & H+ are produced per cycle of the citric acid cycle?
Which of the following is NOT a major regulatory step in the Kreb cycle?
Which of the following is NOT a major regulatory step in the Kreb cycle?
What type of enzyme is fumarase classified as?
What type of enzyme is fumarase classified as?
In terms of energy yield, how many GTP (ATP equivalents) are produced per glucose molecule in the Kreb cycle?
In terms of energy yield, how many GTP (ATP equivalents) are produced per glucose molecule in the Kreb cycle?
Which enzyme serves as the 'gatekeeper' for the Kreb cycle?
Which enzyme serves as the 'gatekeeper' for the Kreb cycle?
What happens to all steps during the Kreb cycle where CO2 is released?
What happens to all steps during the Kreb cycle where CO2 is released?
Flashcards
Kreb Cycle
Kreb Cycle
A metabolic cycle that breaks down food molecules into carbon dioxide, regenerating the starting molecule.
Acetyl group
Acetyl group
A two-carbon molecule added to oxaloacetate to begin the Krebs Cycle.
Oxaloacetate
Oxaloacetate
A small molecule that acts as a starting point and regenerating product in the Krebs Cycle.
8 metabolic reactions
8 metabolic reactions
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Citrate Synthase
Citrate Synthase
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Carbon Dioxide Release
Carbon Dioxide Release
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Oxaloacetate Regeneration
Oxaloacetate Regeneration
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Metabolic Cycle
Metabolic Cycle
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Isocitrate Dehydrogenase
Isocitrate Dehydrogenase
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What is the product of isocitrate dehydrogenase action?
What is the product of isocitrate dehydrogenase action?
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Cofactors for isocitrate dehydrogenase
Cofactors for isocitrate dehydrogenase
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What is the role of NAD+ in isocitrate dehydrogenase?
What is the role of NAD+ in isocitrate dehydrogenase?
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What happens in the decarboxylation step of isocitrate dehydrogenase?
What happens in the decarboxylation step of isocitrate dehydrogenase?
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Importance of Mg2+ in decarboxylation
Importance of Mg2+ in decarboxylation
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Why is isocitrate dehydrogenase named after oxidation?
Why is isocitrate dehydrogenase named after oxidation?
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What happens to the proton released by NAD+?
What happens to the proton released by NAD+?
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Alpha-Ketoglutarate Dehydrogenase (KGDH)
Alpha-Ketoglutarate Dehydrogenase (KGDH)
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KGDH Mechanism
KGDH Mechanism
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Succinyl-CoA
Succinyl-CoA
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CoASH
CoASH
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TPP (Thiamine Pyrophosphate)
TPP (Thiamine Pyrophosphate)
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Lipoamide
Lipoamide
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FAD (Flavin Adenine Dinucleotide)
FAD (Flavin Adenine Dinucleotide)
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Fumarase
Fumarase
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Malate Dehydrogenase
Malate Dehydrogenase
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Energy Yield per Krebs Cycle
Energy Yield per Krebs Cycle
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Energy Yield per Glucose
Energy Yield per Glucose
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Regulation of the Krebs Cycle
Regulation of the Krebs Cycle
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Pyruvate Dehydrogenase
Pyruvate Dehydrogenase
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Alpha-ketoglutarate Dehydrogenase
Alpha-ketoglutarate Dehydrogenase
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Succinyl-CoA Synthetase
Succinyl-CoA Synthetase
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Succinate Dehydrogenase
Succinate Dehydrogenase
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FAD in Succinate Dehydrogenase
FAD in Succinate Dehydrogenase
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Succinate Dehydrogenase and ETC
Succinate Dehydrogenase and ETC
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Transferring Electrons from FADH2
Transferring Electrons from FADH2
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Complex II
Complex II
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Citric Acid Cycle
Citric Acid Cycle
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What is the starting molecule of the citric acid cycle?
What is the starting molecule of the citric acid cycle?
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What is the role of citrate synthase in the citric acid cycle?
What is the role of citrate synthase in the citric acid cycle?
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What is isocitrate?
What is isocitrate?
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What is the role of isocitrate dehydrogenase?
What is the role of isocitrate dehydrogenase?
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What is alpha-ketoglutarate dehydrogenase complex?
What is alpha-ketoglutarate dehydrogenase complex?
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What is the role of succinyl-CoA synthetase?
What is the role of succinyl-CoA synthetase?
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What is the purpose of the electron transport chain?
What is the purpose of the electron transport chain?
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Study Notes
The Krebs Cycle
- The Krebs Cycle, also known as the Citric Acid Cycle or Tricarboxylic Acid Cycle, is a central metabolic pathway.
- It plays a critical role in energy production and biosynthesis.
- The cycle completes the breakdown of sugars, started in glycolysis, and fuels ATP production.
- It also serves as a central hub for biosynthetic reactions, creating intermediates for amino acid and other molecule building.
- The cycle consists of 8 metabolic reactions, fully oxidizing food molecules to carbon dioxide.
Krebs Cycle Overview
- The Krebs Cycle's 8 reactions use oxaloacetate as a starting point.
- An acetyl group is added to oxaloacetate, initiating the cycle.
- In a series of eight steps, the acetyl group is completely broken down.
- The oxaloacetate is regenerated, allowing the cycle to repeat.
- The cycle does not directly remove just two carbon atoms, but involves a careful shuffling of atoms.
- Two carbons that originally belonged to oxaloacetate are released as carbon dioxide.
- The original acetate atoms are rearranged to recreate oxaloacetate.
Krebs Cycle Reactions
- The cycle involves 8 major reactions.
- It's a metabolic cycle, meaning it regenerates the initial molecule, oxaloacetate.
Reaction 1: Citrate Synthase
- The first reaction combines oxaloacetate and acetyl-CoA to form citrate.
- Coenzyme A is released in the process.
- The carboxylic acid groups in citrate originate from oxaloacetate, while the acetate-derived group and methyl groups are in red.
Reaction 2: Aconitase
- Aconitase catalyzes the isomerization of citrate to isocitrate.
- An intermediate named cis-aconitate forms during the reaction.
- This step is often omitted in diagrams of the cycle.
Reaction 3: Isocitrate Dehydrogenase
- Isocitrate is oxidized and decarboxylated to α-ketoglutarate.
- Carbon dioxide is released.
- NADH is produced.
- Key cofactor: NAD+.
Reaction 4: α-Ketoglutarate Dehydrogenase
- A very similar mechanism to the PDH Complex occurs.
- Carbon dioxide is released and NADH is also formed.
- This forms succinyl-CoA.
Reaction 5: Succinyl-CoA Synthetase
- This creates GTP (a molecule equivalent to ATP) through GDP phosphorylation, releasing coenzyme A in the process.
- This creates succinate.
Reaction 6: Succinate Dehydrogenase
- This enzyme oxidizes succinate to form fumarate.
- FAD is involved as an electron carrier, producing FADH2.
- It is part of the electron transport chain.
Reaction 7: Fumarase
- This lyase (enzyme) converts fumarate to malate, via the addition of water.
Reaction 8: Malate Dehydrogenase
- Malate is oxidized to oxaloacetate, generating NADH.
- Oxaloacetate is regenerated, thus completing the Krebs Cycle.
Energy Yield
- In one turn of the cycle, 3 NADH/H+, 1 FADH2, and 1 GTP (equivalent to ATP) are produced.
- For a glucose molecule, which is split into two acetyl-CoA, 6 pairs of NADH and two pairs of FADH2 are generated.
- For each glucose molecule, two turns of the Krebs Cycle yield 2 GTP (ATP equivalents), 6 NADH/H+ and 2 FADH2.
Regulation of the Krebs Cycle
- Several major dehydrogenase enzymes regulate this pathway, including pyruvate dehydrogenase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.
- They are highly sensitive to the energy levels within the cell.
- High NADH or ATP, for example, results in inactivation as part of negative feedback.
Beriberi
- Thiamine deficiency (Vitamin B1) leads to inefficient TPP coenzyme production.
- This results in impaired function of PDH and α-ketoglutarate dehydrogenase.
- Symptoms include weight loss, emotional disturbances, sensory/limb weakness, and irregular heartbeat.
Electron Transport Chain
- The next stage uses the electrons harvested from the Krebs Cycle in the mitochondrial electron transport chain to produce ATP.
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Description
Explore the intricacies of the Krebs Cycle, also known as the Citric Acid Cycle, a vital metabolic pathway in energy production and biosynthesis. This quiz covers the eight metabolic reactions involved in the cycle, how it utilizes oxaloacetate, and its role in ATP production. Test your understanding of its function and significance in cellular respiration.
