During cellular respiration, how many turns of the Krebs cycle are there for each molecule of pyruvate?
To determine the number of turns of the Krebs cycle for each molecule of pyruvate during cellular respiration, you need to understand the process and steps involved.
The Krebs cycle, also known as the citric acid cycle, is an essential part of cellular respiration, which occurs in the mitochondria of eukaryotic cells. It is the second stage in the breakdown of glucose and serves to produce energy-rich molecules such as ATP.
Let's break down the steps involved in the Krebs cycle:
1. Pyruvate Decarboxylation: Before the Krebs cycle begins, each molecule of pyruvate (generated during glycolysis) undergoes decarboxylation, where one carbon is removed in the form of carbon dioxide (CO2) to produce acetyl-CoA—a two-carbon molecule.
2. Acetyl-CoA Entry: Acetyl-CoA enters the Krebs cycle by combining with a four-carbon molecule called oxaloacetate, forming a six-carbon molecule called citrate.
3. Conversion and Decarboxylation: Through a series of enzymatic reactions, citrate undergoes a rearrangement and decarboxylation, releasing two carbon dioxide molecules. This yields a four-carbon molecule called succinyl-CoA.
4. Energy Production: The resulting succinyl-CoA is further broken down, releasing energy in the form of ATP and high-energy electron carriers (NADH and FADH2). Additionally, malate is formed, which is later converted back to oxaloacetate.
5. Regeneration of Oxaloacetate: The last step of the Krebs cycle involves the regeneration of oxaloacetate, which can then combine with another acetyl-CoA to begin the cycle again.
Now, back to the original question: How many turns of the Krebs cycle occur for each molecule of pyruvate?
During one round of the Krebs cycle, which starts with oxaloacetate and ends with its regeneration, only one molecule of pyruvate is involved.
However, it is important to note that during the breakdown of glucose, two molecules of pyruvate are produced from each glucose molecule. Therefore, for each glucose molecule, the Krebs cycle occurs twice, once for each molecule of pyruvate formed during glycolysis.
In summary, for each molecule of pyruvate, one complete turn of the Krebs cycle occurs during cellular respiration. However, considering both pyruvate molecules from glucose, the Krebs cycle occurs twice overall.