Lecture Notes: Aerobic Respiration - The Krebs Cycle
Introduction
- Krebs Cycle is a key process in aerobic respiration.
- It's not the final part, but essential for breaking down the organic molecule completely.
Overview
- Starts with glucose → glycolysis → pyruvate → link reaction → acetyl-CoA.
- Acetyl-CoA enters Krebs Cycle.
- Occurs in the mitochondrial matrix.
Key Steps in Krebs Cycle
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Formation of Citrate
- Acetyl group (2C) joins with oxaloacetate (4C) → Citrate (6C).
- Co-enzyme A detaches after delivering acetyl group.
- Important to remember: the cycle regenerates oxaloacetate.
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Decarboxylation and Dehydrogenation
- Decarboxylation: removal of carbon as CO2.
- Dehydrogenation: removal of hydrogen, accepted by NAD → reduced NAD.
- Citrate (6C) becomes a 5C molecule.
- Second decarboxylation and dehydrogenation: 5C to 4C molecule.
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Substrate-Level Phosphorylation
- Energy released to synthesize ATP from ADP and phosphate.
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Further Dehydrogenation
- Step 5: Hydrogen accepted by FAD, forming reduced FAD.
- Step 6: Another NAD accepts hydrogen → reduced NAD.
Final Products (Per Cycle)
- Carbon Dioxide: 4 CO2
- Reduced NAD: 6 NADH
- Reduced FAD: 2 FADH2
- ATP: 2 ATP
Additional Notes
- No need to remember intermediate 5C, 4C molecules' names during the cycle.
- Krebs Cycle processes 2 acetyl-CoA molecules, hence doubling the products listed above.
Important Terms
- Oxaloacetate: 4-carbon molecule; regenerated at the end of the cycle.
- Citrate: 6-carbon molecule; formed from oxaloacetate and acetyl group.
- NAD/FAD: Electron carriers, crucial for oxidation-reduction reactions in the cycle.
Summary
- Krebs Cycle is a series of reactions important for energy production.
- Key focus: breaking down acetyl group for energy extraction.
- Produces crucial reducing agents (NADH, FADH2) for further steps in aerobic respiration.
By understanding the main steps and outputs of the Krebs Cycle, we can appreciate its role in cellular respiration and energy production.