Krebs Cycle Overview and Reactions
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Questions and Answers

What is the role of Coenzyme A in the process described?

  • It generates ATP
  • It forms a thioester with the succinyl group (correct)
  • It acts as a hydrogen carrier
  • It oxidizes fumarate

What does the lipoamide cofactor primarily accomplish during the enzymatic function?

  • It reduces FAD to FADH2 (correct)
  • It fully oxidizes succinate
  • It directly produces GTP
  • It transfers electrons to NAD+

What substance is produced by the Succinyl-CoA synthetase during its reaction?

  • Coenzyme A
  • GTP (correct)
  • NADH
  • Fumarate

What is the final product of the reaction catalyzed by succinate dehydrogenase?

<p>Fumarate (D)</p> Signup and view all the answers

How does succinate dehydrogenase connect the citric acid cycle to the electron transport chain?

<p>By transferring electrons to FAD and linking with Complex II (B)</p> Signup and view all the answers

What type of enzymatic reactions does succinate dehydrogenase perform?

<p>Oxidoreductase and lyase (B)</p> Signup and view all the answers

What occurs to the electrons transferred from FADH2 during the reactions described?

<p>They are moved to NAD+ for transport to the ETC (B)</p> Signup and view all the answers

What is the primary function of the succinyl group in the context of succinyl-CoA synthetase?

<p>To phosphorylate GDP (B)</p> Signup and view all the answers

What is the starting molecule of the Kreb Cycle?

<p>Oxaloacetate (D)</p> Signup and view all the answers

How many metabolic reactions occur in the Kreb Cycle?

<p>8 (C)</p> Signup and view all the answers

What is the primary function of the Kreb Cycle?

<p>Oxidize food molecules to carbon dioxide (C)</p> Signup and view all the answers

Which molecule is released as a product during the Kreb Cycle?

<p>Carbon dioxide (D)</p> Signup and view all the answers

What happens to the original oxaloacetate at the end of the Kreb Cycle?

<p>It is regenerated for another cycle (D)</p> Signup and view all the answers

Which process occurs during the shuffling of carbon atoms in the Kreb Cycle?

<p>Decarboxylation releasing CO2 (B)</p> Signup and view all the answers

Which enzyme initiates the Kreb Cycle by combining acetyl group with oxaloacetate?

<p>Citrate Synthase (A)</p> Signup and view all the answers

What is the result of the eight steps in the Kreb Cycle on the acetyl group?

<p>It is fully oxidized and converted to CO2 (A)</p> Signup and view all the answers

What molecule is formed from alpha-ketoglutarate during the reaction catalyzed by alpha-ketoglutarate dehydrogenase?

<p>Succinyl-CoA (C)</p> Signup and view all the answers

Which cofactor does alpha-ketoglutarate dehydrogenase use that is also utilized by pyruvate dehydrogenase?

<p>CoASH (C)</p> Signup and view all the answers

What is released during the reaction catalyzed by alpha-ketoglutarate dehydrogenase?

<p>Carbon dioxide (CO2) (C)</p> Signup and view all the answers

Which of the following statements is true about the reaction mechanism of alpha-ketoglutarate dehydrogenase?

<p>It has a mechanism similar to that of the PDH complex. (A)</p> Signup and view all the answers

During the reaction of alpha-ketoglutarate dehydrogenase, which component mediates the release of CO2?

<p>TPP (B)</p> Signup and view all the answers

What does the remaining succinyl group get transferred to during the reaction catalyzed by alpha-ketoglutarate dehydrogenase?

<p>Lipoamide (C)</p> Signup and view all the answers

Which of the following cofactors is not used by alpha-ketoglutarate dehydrogenase?

<p>ATP (B)</p> Signup and view all the answers

How does the mechanism of alpha-ketoglutarate dehydrogenase compare to other dehydrogenases?

<p>It has a similar mechanism to some but differs significantly from others. (C)</p> Signup and view all the answers

Flashcards

Kreb Cycle Reactions

Eight metabolic reactions involved in the complete oxidation of food molecules into carbon dioxide, regenerating the starting molecule.

Oxaloacetate

A small molecule that acts as the starting point for the Krebs Cycle.

Acetyl Group

The group added to oxaloacetate to initiate the Krebs Cycle reactions.

Citrate Synthase

An enzyme involved in the first step of the Krebs cycle.

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Aconitase

An enzyme that catalyzes the second step of the Krebs cycle.

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Isocitrate Dehydrogenase

An enzyme that catalyzes a reaction in the Krebs Cycle.

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a-ketoglutarate Dehydrogenase

An enzyme involved in the Krebs Cycle which plays a crucial role in the process.

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Succinyl-CoA Synthetase

An enzyme that catalyzes a reaction in the Krebs Cycle.

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Isocitrate Dehydrogenase

An enzyme that catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate, releasing CO2 and producing NADH.

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Ketone Formation

The process where a carbonyl group forms, usually from an oxidation reaction, during the citric acid cycle.

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alpha-Ketoglutarate Dehydrogenase (KGDH)

An enzyme complex that catalyzes the oxidative decarboxylation of alpha-ketoglutarate to succinyl-CoA, releasing CO2, NADH, and a proton.

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PDH Complex

Pyruvate Dehydrogenase Complex; a multi-enzyme complex responsible for converting pyruvate to acetyl-CoA.

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Oxidative Decarboxylation

A chemical reaction that involves both oxidation (loss of electrons) and decarboxylation (loss of a CO2 molecule) in a single step.

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Succinyl-CoA

A molecule produced in the citric acid cycle following the oxidation of alpha-ketoglutarate, a key intermediate.

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Coenzyme A (CoA)

A coenzyme essential for many metabolic reactions, including the conversion of alpha-ketoglutarate and pyruvate.

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TPP, Lipoamide, FAD, NAD+

Important coenzymes/cofactors for alpha-ketoglutarate dehydrogenase complex, acting as electron carriers and intermediates in the oxidation reaction.

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Succinyl-CoA Synthetase Role

An enzyme that produces GTP (ATP equivalent) by phosphorylating GDP, releasing Coenzyme A and forming succinate.

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Succinate Dehydrogenase Function

Oxidizes succinate to fumarate, transferring electrons to FAD, and linking to the electron transport chain (as complex II).

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Lipoamide Cofactor Role

A crucial molecule that accepts and releases electrons during enzymatic reactions, oxidizing and reducing succinyl-CoA synthesis

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Succinyl Group Transfer

The succinyl group attached to Coenzyme A in the E2 complex is transferred to Coenzyme-A as a thioester, releasing it from the enzyme.

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FAD's role in Krebs Cycle

Accepting electrons from lipoamide (reduced state) and transferring them to NAD+ for transport to the electron transport chain.

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Succinate Oxidation

Process of converting succinate to fumarate through the action of succinate dehydrogenase.

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Mitochondrial Membrane Binding

Succinate dehydrogenase (complex II) is bound within the mitochondrial membrane, connecting the Krebs cycle directly to the electron transport chain.

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Electron Transport Chain Link

The succinate dehydrogenase complex directly transfers electrons to the electron transport chain, streamlining electron transfer in cellular respiration.

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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 crucial metabolic process.
  • It's central to cellular metabolism, playing a vital role in energy production and biosynthesis.
  • The cycle completes the breakdown of sugars started in glycolysis.
  • It's a key part of producing ATP.
  • It's also a hub for amino acid and other molecule synthesis.
  • The cycle occurs in the mitochondrial matrix.

Krebs Cycle Overview

  • The Krebs Cycle involves 8 metabolic reactions.
  • The cycle uses a small molecule, oxaloacetate, as a starting and ending point.
  • Acetyl-CoA combines with oxaloacetate to begin the cycle.
  • The acetyl group is then broken down in 8 steps.
  • Oxaloacetate is regenerated at the end of the cycle.
  • Two carbon atoms are released as carbon dioxide in each cycle turn.
  • The 8 reactions use enzymes.

Krebs Cycle Reactions (Detailed)

  • Reaction 1: Citrate Synthase: Acetyl-CoA combines with oxaloacetate to form citrate. CoASH is released.

  • Reaction 2: Aconitase: Citrate is isomerized to isocitrate. (Intermediate cis-aconitate exists).

  • Reaction 3: Isocitrate Dehydrogenase: Isocitrate is oxidized and decarboxylated, forming α-ketoglutarate. NADH and CO2 are produced.

  • Reaction 4: α-Ketoglutarate Dehydrogenase: α-ketoglutarate is oxidized and decarboxylated, producing succinyl-CoA, NADH, and CO2.

  • Reaction 5: Succinyl-CoA Synthetase: Succinyl-CoA is converted to succinate, producing GTP (equivalent to ATP).

  • Reaction 6: Succinate Dehydrogenase: Succinate is oxidized to fumarate, producing FADH2. This enzyme is part of the electron transport chain.

  • Reaction 7: Fumarase: Fumarate is hydrated to form malate.

  • Reaction 8: Malate Dehydrogenase: Malate is oxidized to oxaloacetate, producing NADH.

Energy Yield of the Krebs Cycle

  • Per cycle, the process yields 3 NADH/H+, 1 FADH2, and 1 GTP.
  • Per glucose molecule (2 cycles), the total yield translates to 6 NADH/H+, 2 FADH2, and 2 GTP.

Regulation of the Krebs Cycle

  • The cycle is mainly controlled by three key dehydrogenase enzymes: pyruvate dehydrogenase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.
  • These enzymes are sensitive to energy levels in the cell.
  • High levels of NADH, Acetyl-CoA, and ATP inhibit the cycle.
  • Low levels of these molecules (e.g., high ADP) activate the cycle.

Beriberi

  • A deficiency in vitamin B1 can cause Beriberi.
  • This vitamin is essential for the TPP cofactor.
  • Without sufficient TPP, the Krebs Cycle enzymes (PDH and α-ketoglutarate DH) function less efficiently, reducing ATP production.
  • Low ATP levels lead to various symptoms like weight loss, emotional disturbances, and neurological/muscular issues.

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Related Documents

Kreb Cycle Part 2: The Reactions PDF

Description

Explore the intricate details of the Krebs Cycle, a fundamental metabolic process vital for energy production and biosynthesis. This quiz covers key reactions, the role of enzymes, and the regeneration of oxaloacetate. Test your knowledge on the steps involved in this critical cycle.

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