Lesson 5.4 - Citric Acid Cycle
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Questions and Answers

What is the net ATP produced per glucose during glycolysis?

2 ATP

In what specific location within the cell does the Citric Acid Cycle occur?

Mitochondrial matrix

What is another common name for the Citric acid cycle?

Krebs cycle

What is the total number of NADH produced per glucose molecule across glycolysis, pyruvate oxidation, and the citric acid cycle?

<p>10 NADH</p> Signup and view all the answers

What is the total amount of ATP produced per glucose molecule by the combination of glycolysis and the citric acid cycle?

<p>4 ATP</p> Signup and view all the answers

How many FADH2 molecules are made per glucose molecule via the citric acid cycle?

<p>2 FADH2</p> Signup and view all the answers

What molecule initiates the citric acid cycle?

<p>Acetyl Co-A</p> Signup and view all the answers

How many molecules of carbon dioxide (CO2) are produced per pyruvic acid via the citric acid cycle?

<p>3 CO2</p> Signup and view all the answers

What are the total products released per glucose molecule through the Citric acid cycle?

<p>6 CO2, 10 NADH, 2 FADH2, 4 ATP</p> Signup and view all the answers

What are the products of pyruvate oxidation per starting glucose molecule?

<p>2 Acetyl Co-A, 2 NADH, 2 CO2</p> Signup and view all the answers

Prior to entering the citric acid cycle, what critical modification occurs to pyruvic acid?

<p>Pyruvic acid loses one carbon atom, forming acetate, which then binds to Coenzyme A forming acetyl-CoA.</p> Signup and view all the answers

How many carbon dioxide ($CO_2$) molecules are released per molecule of pyruvic acid during the citric acid cycle, including pyruvic acid oxidation?

<p>Three</p> Signup and view all the answers

What is the significance of OAA (oxaloacetate) in the citric acid cycle?

<p>OAA combines with acetyl-CoA, initiating the cycle, and is regenerated at the end of the cycle, allowing the process to continue.</p> Signup and view all the answers

Besides ATP, what are the other energy-carrying molecules produced per pyruvate in the citric acid cycle?

<p>NADH and FADH2.</p> Signup and view all the answers

What is the role of coenzyme A in the transition step of pyruvic acid to the citric acid cycle?

<p>Coenzyme A binds to the acetate formed from pyruvic acid, creating acetyl-CoA.</p> Signup and view all the answers

Explain how the citric acid cycle is dependent on the presence of oxygen.

<p>While the citric acid cycle itself does not directly use oxygen, it cannot occur without oxygen because the electron carriers (NADH and FADH2) produced by the cycle require oxygen at the electron transport chain.</p> Signup and view all the answers

If the citric acid cycle starts with one molecule of glucose, how many molecules of ATP are generated directly?

<p>Two</p> Signup and view all the answers

What is the immediate product formed when acetyl-CoA combines with OAA?

<p>Citric acid</p> Signup and view all the answers

How does the formation of NADH and $FADH_2$ contribute to the overall energy yield of cellular respiration?

<p>NADH and $FADH_2$ carry high-energy electrons to the electron transport chain, where they are used to generate a large amount of ATP.</p> Signup and view all the answers

Briefly describe the fate of the carbon atoms from pyruvic acid as it proceeds through the citric acid cycle.

<p>The carbon atoms from pyruvic acid are released as carbon dioxide molecules during the cycle.</p> Signup and view all the answers

Flashcards

Pyruvate Oxidation

Pyruvic acid is converted into acetyl CoA, a 2-carbon compound. This process releases CO2 and generates NADH, which carries electrons for ATP production.

Citric Acid Cycle

A series of reactions that occur in the mitochondrial matrix, breaking down acetyl CoA into CO2 and generating ATP, NADH, and FADH2.

Oxaloacetate (OAA)

A 4-carbon molecule that combines with acetyl CoA to begin the Citric Acid Cycle.

Citric Acid

The first stable product of the Citric Acid Cycle, formed by the combination of acetyl CoA and oxaloacetate.

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NADH

A molecule that carries electrons from the Citric Acid Cycle to the electron transport chain, where they are used to generate ATP.

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FADH2

A molecule that carries electrons from the Citric Acid Cycle to the electron transport chain, where they are used to generate ATP.

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Coenzyme

An organic molecule required by enzymes to function properly. In the citric acid cycle, Coenzyme A is crucial for the formation of acetyl CoA

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ATP Production in Citric Acid Cycle

The net gain of ATP from one molecule of glucose in the citric acid cycle is 2 ATP.

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Location of Citric Acid Cycle

The Citric Acid Cycle occurs in the mitochondrial matrix, the innermost compartment of mitochondria.

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Alternative name for the Citric Acid Cycle

Krebs Cycle

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What is the Citric Acid Cycle?

The Citric Acid Cycle (Krebs Cycle) is a series of chemical reactions that occur in the mitochondrial matrix of eukaryotic cells. It is a central metabolic pathway in the breakdown of carbohydrates, fats, and proteins to produce energy in the form of ATP.

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What is the starting molecule for the Citric Acid Cycle?

Acetyl Coenzyme A (Acetyl CoA) is the starting molecule for the Citric Acid Cycle. It is a two-carbon molecule that is produced by the breakdown of pyruvate during pyruvate oxidation.

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How much CO2 is produced per pyruvic acid through the citric acid cycle?

For each molecule of pyruvate, the Citric Acid Cycle produces 3 molecules of CO2.

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What are the products released per glucose through the Krebs cycle?

Glycolysis, pyruvate oxidation, and the Citric Acid Cycle together produce 6 CO2 molecules, 10 NADH molecules, 2 FADH2 molecules, and 4 ATP molecules per glucose molecule.

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What is the net ATP produced per glucose in the Krebs cycle?

The complete breakdown of glucose through glycolysis, pyruvate oxidation, and the Citric Acid Cycle produces a net gain of 2 ATP. This energy is primarily released through the electron transport chain.

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What are the products of Pyruvate oxidation, per glucose?

The oxidation of one molecule of pyruvate produces 2 molecules of Acetyl CoA, 2 molecules of NADH, and 2 molecules of CO2.

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How many NADH molecules are produced per glucose in the citric acid cycle?

The Citric Acid Cycle generates 8 NADH molecules per glucose molecule, which are then used in the electron transport chain to produce ATP.

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How many FADH2 molecules are produced per glucose in the citric acid cycle?

The Citric Acid Cycle generates 2 FADH2 molecules per glucose molecule, which are then used in the electron transport chain to produce ATP.

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What is the role of the electron transport chain?

The electron transport chain, located in the inner mitochondrial membrane, uses the electrons carried by NADH and FADH2 to generate a proton gradient, which drives the synthesis of ATP, the energy currency of the cell.

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Where does the Citric Acid Cycle occur?

The Citric Acid Cycle takes place exclusively in the mitochondrial matrix, the inner compartment of the mitochondria. It requires oxygen and is therefore an aerobic process.

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Study Notes

Lesson 5.4 - Cellular Respiration - Citric Acid Cycle

  • The citric acid cycle is a step in cellular respiration that requires oxygen
  • Pyruvic acid, produced in glycolysis, passes to the mitochondrial matrix for the citric acid cycle, also known as the Krebs cycle
  • The citric acid cycle breaks down pyruvic acid into carbon dioxide, releasing energy
  • During the citric acid cycle, high-energy electrons are released that are used to generate ATP in the electron transport chain (ETC)

Pyruvic Acid Oxidation

  • This occurs before the Krebs cycle begins, in the Krebs cycle
  • It removes one carbon molecule from pyruvic acid to produce acetate
  • Carbon dioxide is released during this process
  • NAD+ is reduced to NADH

Coenzyme A and Pyruvic Acid Oxidation

  • Coenzymes are organic molecules, non-protein, needed for enzyme function
  • Coenzyme A joins the acetate, creating acetyl CoA

Citric Acid Cycle - Key Steps

  • Acetyl CoA enters the citric acid cycle by combining with a 4-carbon compound (oxaloacetate), forming the first stable product-citric acid
  • Citric acid is broken down into a 5-carbon compound and then a 4-carbon compound
  • Oxaloacetate is regenerated, continuing the cycle.

Krebs Cycle Products per Pyruvate

  • Two more carbon dioxide molecules are released
  • Three NADH molecules are formed
  • One FADHâ‚‚ molecule is formed
  • One molecule of ATP is generated

Citric Acid Cycle - Summary

  • The citric acid cycle breaks down one pyruvate molecule into 3 molecules of COâ‚‚
  • Produces energy from 1 molecule of pyruvic acid in the form of 4 NADH, 1 FADHâ‚‚, and 1 ATP
  • In the presence of oxygen, the high-energy electrons can be used to produce a large amount of ATP in the electron transport chain.

Review Questions (Answers)

    1. Net gain of ATP from 1 glucose in the citric acid cycle, is 2 ATP
    1. Citric acid cycle takes place in the mitochondrial matrix
    1. Another name for the citric acid cycle is the Krebs cycle.
    1. Gain of NADH per glucose through the citric acid cycle is 8 NADH
    1. Gain of ATP per glucose through citric acid cycle is 2 ATP
    1. Gain of FADHâ‚‚ per pyruvic acid in the citric acid cycle is 2 FADHâ‚‚
    1. Starting molecule for citric acid cycle is Acetyl CoA
  • 8.Amount of COâ‚‚ produced per pyruvic acid in the citric acid cycle is 3 COâ‚‚
  • 9.Products released per glucose in the Krebs cycle are 6 COâ‚‚, 8 NADH, 2 FADHâ‚‚, and 2 ATP.
    1. Products of pyruvate oxidation per glucose is 2 acetyl CoA, 2 NADH, and 2 COâ‚‚.

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