Respiration
What is a redox reaction and what is respiration? During a redox reaction an element is being oxidized while another element is being reduced. There are two different chemical processes happening at the same time, and an electron transferring is occurring where the oxidant in the reaction attracts electrons. Redox reactions are very common even though it’s hard to believe. Approximately 1/3 of all reactions in our environment are chemical reactions of this sort. We will talk about the most common redox reaction right now, that is respiration. Respiration is what’s happening when you breath and get an oxygen supply to the cells, and it’s also about how the cells convert food from you to energy, after a series of redox reactions. Glycolysis and the Citric Acid cycle are in focus at that moment. It’s all happening in the inner membrane of the mitochondria (an organelle with its own DNA that has evolved from a bacteria).
Photosynthesis where the outcome is oxygen is not respiration. Still both plants and animals (and bacteria, fungi, and everything that lives) have a gas exchange between themselves and the environment. When there is plenty of glucose then the cells start to produce Acetyl-CoA (which is an intermediate in the cell metabolism). We get Acetyl-CoA when glucose is broken down (catabolism happened) or when fatty acids are being oxidized. This molecule in question participates in many reactions that involve lipids, macromolecules and polysaccharides etc.. One glucose molecule has 6 carbons (C), and these will become 3 pyruvate molecules with 3 C each, during catabolism. When a pyruvate goes from cytoplasm where it was made, into the mitochondria where we get closer to the power generation, then 1 C departs as carbon dioxide. Simultaneously as this happens, we get Acetyl-CoA.
We also get a lot of Acetyl-CoA during beta-oxidation, when fats are broken down to fatty acids. As you can see, we get Acetyl-CoA from two different sources, and that molecules main function will be to deliver the acetyl-group to the inner membrane of the mitochondria, so it can be oxidized so the cell gets its energy. When Acetyl-CoA goes into the citric acid cycle from two directions then 2 carbons are immediately oxidized to CO2 (carbon dioxide). The next step after citric acid cycle is the electron transport chain, and this is also happening inside the mitochondrial inner membrane. During oxidations in citric acid cycle, we got a lot of hydrogen ions (H+) and energy-rich electrons. These are doing so NADH + H^+ and FADH2 can be created and going inside the electron transport chain. Here in this step the final energy recovery will happen. These two molecules has carried electrons so the end product can be ATP (energy-carrying molecule) and water.
Feel free to read more from a different source, National Library of Medicine: https://www.ncbi.nlm.nih.gov/books/NBK9896/ And the picture below is borrowed from Google.
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