Questions and Answers
What happens to pyruvate as it enters into mitochondria? Name products/coenzymes of this reaction if any.
Pyruvate turns into Acetyl-CoA (a 2 carbon molecule) by adding NAD and CoA, releasing NADH and CO2.
Where would you draw the line dividing the three stages of the citric acid cycle?
The line is drawn between the pyruvate transport stage and the CO2 emission step, and again between CO2 emission and oxaloacetate reformation stage.
Memorize all the intermediates in the citric acid cycle and the number of carbons in each.
Acetyl-CoA (2 carbons), Citrate (6 carbons), Isocitrate (6 carbons), Alpha-Ketoglutarate (5 carbons), others are 4 carbons.
What are the products of the citric acid cycle and where are they given off?
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How many ATP are made during the citric acid cycle? What are the intermediate steps in ATP formation from Succinyl-CoA?
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What is the reaction step involved in the breakdown of pyruvate?
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What is FAD and is it the reduced or oxidized form?
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How many ATP are produced from one pyruvate that enters the citric acid cycle? How many per glucose?
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How many reduced cofactors are produced in the citric acid cycle per glucose? What is their fate?
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Which do we do first, produce CO2 or consume O2?
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Where do proteins and fats enter the Krebs cycle?
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Study Notes
Pyruvate Transformation
- Pyruvate is converted to Acetyl-CoA (2 carbons) upon entering mitochondria.
- This conversion involves NAD and CoA, producing NADH and releasing CO2.
- Acetyl-CoA combines with Oxaloacetate (4 carbons) to form Citrate (6 carbons).
Stages of the Citric Acid Cycle
- The cycle has three stages: Pyruvate transport, CO2 emission, and Oxaloacetate reformation.
- The transition from pyruvate to Acetyl-CoA marks the division between transport and CO2 emission stages.
- The conversion of Succinyl-CoA to Succinate indicates the end of CO2 emission and the start of the oxaloacetate reformation stage.
Intermediates and Their Carbon Counts
- Key intermediates include:
- Acetyl-CoA (2C), Citrate (6C), Isocitrate (6C), and Alpha-Ketoglutarate (5C).
- Succinyl-CoA, Succinate, Fumarate, Malate, and Oxaloacetate are 4 carbons each.
Products of the Citric Acid Cycle
- The cycle yields 3 NADH, 1 FADH2, and 1 ATP per turn.
- It occurs in the mitochondrial matrix, producing chemical energy from oxidized pyruvate.
ATP Production and Intermediate Steps
- 1 ATP is produced from each pyruvate entering the cycle, with no ATP consumed during the cycle.
- For each glucose, 2 ATP are generated (1 from each pyruvate).
- Intermediate steps to ATP formation involve GDP conversion to GTP, which is then converted to ATP.
Breakdown of Pyruvate
- Pyruvate breakdown parallels the transformation of Succinyl-CoA to Succinate.
- ADP and inorganic phosphate (Pi) combine to form ATP while CoA is released.
Role of FAD
- FAD (Flavin adenine dinucleotide) is an oxidized electron carrier in the cycle.
- It accepts electrons during the reactions, playing a key role in energy transfer.
Reduced Cofactors Production
- Each cycle produces 3 NADH, 1 FADH2, and generates 2 CO2, among other products.
- The process for one glucose results in double the products since each glucose generates 2 pyruvates.
- NADH and FADH2 are utilized in the electron transport chain, CO2 is released, ATP is used for cellular work, and CoA is recycled.
Cellular Respiration and Gas Exchange
- O2 is consumed before CO2 is produced; oxygen is vital for cellular respiration.
- Oxygen availability affects metabolic processes, illustrated by the difficulty of respiration at high altitudes, such as Mount Everest.
Entry Points for Biomolecules
- Proteins enter the cycle at Alpha-Ketoglutarate, requiring conversion of Glutamate.
- Fats are metabolized to Acetyl-CoA and enter the cycle at the initial stage.
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Description
Test your knowledge on the Citric Acid Cycle with these flashcards that cover the transformation of pyruvate and the various stages of the cycle. Dive into the mechanisms, products, and coenzymes involved in this crucial metabolic pathway. Perfect for biochemistry students looking to reinforce their understanding.
