Questions and Answers
What happens if molecular oxygen is available to the cell?
Glycolysis releases less than a quarter of the chemical energy in glucose; if molecular oxygen is present, the pyruvate enters a mitochondrion, where the oxidation of glucose is completed.
How does pyruvate enter the mitochondrion?
Pyruvate enters the mitochondrion via active transport.
How is the linking glycolysis and the citric acid cycle carried out?
It is carried out in 3 reactions by a multi-enzyme complex.
How does the oxidation of pyruvate to acetyl CoA, the step before the citric acid cycle occur?
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What is the citric acid cycle also known as?
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How does the Krebs cycle work?
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What does FAD stand for?
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Describe steps 1-4 of the citric acid cycle.
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Describe steps 5-8 of the citric acid cycle.
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What makes the Krebs cycle a cycle?
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Name the molecules that conserve most of the energy from the citric acid cycle's redox reactions.
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Study Notes
Glycolysis and Pyruvate
- Glycolysis yields less than 25% of glucose's energy, with the remaining energy stored in pyruvate.
- In the presence of molecular oxygen, pyruvate enters mitochondria for further oxidation in eukaryotic cells, while in prokaryotes, this occurs in the cytosol.
Pyruvate to Acetyl CoA
- Pyruvate enters the mitochondrion through active transport and is converted to acetyl coenzyme A (acetyl CoA).
- This conversion involves a multi-enzyme complex that performs three key reactions, producing CO2 and reducing NAD+ to NADH.
Linking Glycolysis to the Citric Acid Cycle
- Removes a carboxyl group from pyruvate as CO2, which is the first CO2 release in respiration.
- Oxidizes the remaining two-carbon fragment to form acetate, generating NADH.
- Acetyl CoA's formation is highly exergonic, allowing the acetyl group to enter the citric acid cycle.
Citric Acid Cycle Overview
- Known as the tricarboxylic acid cycle or Krebs cycle, named after Hans Krebs.
- Functions as a metabolic furnace, oxidizing pyruvate to release three CO2 molecules.
- Produces 1 ATP per cycle through substrate-level phosphorylation, while transferring energy to NAD+ and FAD.
Components of the Citric Acid Cycle
- FAD stands for flavin adenine dinucleotide, derived from riboflavin (a B vitamin).
- Cycle involves a series of steps where acetyl CoA combines with oxaloacetate to form citrate, which is then transformed through oxidation and decarboxylation processes.
Steps of the Citric Acid Cycle
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Steps 1-4:
- Acetyl CoA adds to oxaloacetate to form citrate.
- Citrate is rearranged to isocitrate.
- Isocitrate loses CO2 and reduces NAD+ to NADH.
- Another CO2 is lost and more NAD+ is reduced, producing a compound attached to coenzyme A.
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Steps 5-8:
- CoA is replaced by a phosphate group that forms GTP.
- FAD is reduced to FADH2 while oxidizing succinate.
- Water is added to rearrange substrate bonds.
- Final oxidation of the substrate reduces NAD+ to NADH and regenerates oxaloacetate.
Regeneration of Oxaloacetate
- The regeneration of oxaloacetate completes the cycle, allowing it to begin anew.
- NADH and FADH2 are key molecules conserving energy during the cycle’s redox reactions, shuttling electrons to the electron transport chain for ATP production.
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Description
Test your understanding of cellular respiration and energy production in eukaryotic and prokaryotic cells with this flashcard quiz. This section focuses on the role of molecular oxygen and the process of glycolysis. Enhance your knowledge by exploring the biochemical pathways involved in energy transfer.
