A Molecular Odyssey through Cellular Respiration

One cliche word you must have heard a hundred or thousand time as a science student is that the mitochondria is the power house of the cell. You see, when we want to explain the cell and energy, the easiest way to say just that way but in reality, it is complex than just that simple saying.

The mitochondria does the job of transferring energy from food and oxygen to the cells so they can perform their different functions such as the cells responsible for allowing your eyes to function properly so you can read this post. They are a key player in cellular respiration and although a lot of us know that it is important for our existence, so many people do not understand its function since it is not visible to them.

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Energy is stored as Adenosine-triphosphate (ATP) in the body which looks like our body's battery that needs refilling at all time when it is used up after powering cellular processes. The average human will require over 100 pounds of ATP a day but since the body doesn't have a permanent and fixed amount of ATP, so the body needs to keep making them, breaking them down, and recycling them, in what we refer to as cellular respiration.

While we are aerobic organisms storing are releasing energy in the presence of oxygen, there are microorganism that store, release, and breakdown ATP in the absence of oxygen, and such case is fermentation. For us aerobic organisms, the process of storing and releasing energy is quite slow through metabolic pathways or chemical reactions.

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This process occurs in three cellular stages starting with glycolysis which is the breaking down of simple glucose when carbs are eaten and glycolysis occurs in the cell's cytoplasm to give out Pyruvate. Pyruvate is also important in other cycles such as the citric acid cycle, and anaerobic respiration. Glycolysis relies on NAD+ as a carrier to release 2 molecules of pyruvate. The NAD+ gives of two electrons and one proton to become NADH- (which is used in the final step of cellular respiration) and H+. After glycolysis with pyruvate oxidation, Citric acid cycle or Kreb cycle begins.

With citric acid cycle, the pyruvate reactant moves from the cell's cytoplasm from the cell's cytoplasm into the mitochondria. It is in this process that some of the CO2 during cellular respiration is made. With the help of a Coenzyme A, Acetyl Coenzyme A is produced. During the kreb cycle, additional ATP is produced, three more molecules of NADH is produced, and FADH2. At the end, we are left with Oxaloacetate which is a four carbon molecule. The Kreb cycle happens twice for every glucose molecule for cellular respiration.

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The third stage of cellular respiration is Oxidative phosphorylation which also occurs in the mitochondria. This is where the majority of the ATP is made. Oxidative phosphorylation and this is where chemical energy becomes mechanical energy. At this stage, proton is being pumped to the intermembrane space. About 10 million ATP is usually produced per seconds in a single cell.

In essence, the journey through cellular respiration intricately converts nutrients into the vital energy currency, ATP, essential for the diverse activities occurring within our cells. Beyond the textbook cliche, understanding the nuanced workings of the mitochondria unveils the remarkable complexity underlying this fundamental biological process.

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Reference

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https://www.ncbi.nlm.nih.gov/books/NBK553175/
https://www.acs.org/molecule-of-the-week/archive/a/adenosine-triphosphate.html
https://www.ncbi.nlm.nih.gov/books/NBK556032/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8091952/
https://www.ncbi.nlm.nih.gov/books/NBK482303/
https://www.khanacademy.org/science/biology/cellular-respiration
https://bio.libretexts.org/Bookshelves/Introductory
https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)