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  • Are you a morning person? One of us is and one if us is definitely not. Mainly because,

  • when I wake up in the morning, it just takes a while for me to feel like I get my energy

  • back. It takes a lot of time---and coffee---for that to happen for me.

  • Cells don't really have that luxury. They are busy performing cell processes all the

  • time and many of the processes

  • that they do require energy. Specifically, ATP energy.

  • ATP stands for adenosine tri phosphate. It's a type of nucleic acid actually, and it is

  • action packed with three phosphates. When the chemical bond that holds the third phosphate

  • is broken, it releases a great amount of energy. It also is converted into ADP, adenosine di

  • phosphate. And really, that's just a fancy way of saying that it has two phosphates after

  • losing one.

  • So where am I going with this? Well, cells have to make this ATP energy. It doesn't

  • really matter what kind of cell you are---prokaryote or eukaryote---you have to make ATP energy.

  • The process for making that ATP energy can be different, however, depending on the type

  • of cell. But you have to make ATP energy.

  • One way that this can be done efficiently is called aerobic cellular respiration. We

  • are going to focus on aerobic in eukaryote

  • cells which have many membrane bound organelles such as mitochondria. The mitochondria is

  • are going to be kind of a big deal in this.

  • So let's get started. Remember we are trying to make ATP energy. Let's take a look at

  • this formula. Remember that reactants (inputs) are on the left side of the arrow. And products

  • (outputs) are on the right side of the arrow.

  • This formula, by the way, looks remarkably similar to photosynthesis. Look how the reactants

  • and products just seem to be on different sides.

  • You know why? See, in photosynthesis, organisms (like plants and protists for example) made

  • glucose. Notice how glucose is a product. But in cellular respiration, we break the

  • glucose. Notice how glucose is a reactant. In order to make ATP energy.

  • So photosynthesis makes glucose---and cellular respiration, it breaks glucose. Kind of cool.

  • Photosynthetic organisms have the best of both worlds because they not only do photosynthesis

  • to make their glucose but they do cellular respiration to break it. I say that's pretty

  • great, because glucose is the starter molecule in cellular respiration and needed in order

  • to get this going. If you aren't photosynthetic, such as a human or an amoeba, you have to

  • find a food source to get your glucose. Cellular respiration involves three major steps. We

  • are going to assume that we are starting with one glucose molecule so that you can see what

  • is produced from one glucose molecule.

  • #1 Glycolysis- This step takes place in the cytoplasm, and this step does not require

  • oxygen. Glucose, the sugar from the formula, is converted into a more usable form called

  • pyruvate. It actually takes a little ATP energy itself to get this process started. The net

  • yield from this step is approximately 2 ATP molecules. And 2 NADH molecules. What is NADH?

  • NADH is a coenzyme, and it has the ability to transfer electrons, which will be very

  • useful in making even more ATP later on. We'll get to that in a minute.

  • #2 Krebs Cycle-This is also called the Citric Acid Cycle. We are now involved in the mitochondria,

  • and this step requires oxygen. The pyruvate that was made is converted and will be oxidized.

  • CO2 (carbon dioxide) is produced. We produce

  • 2 ATP, 6 NADH, and 2FADH2. FADH is also a coenzyme, like NADH, and it will also assist

  • in transferring electrons to make even more ATP.

  • #3 The electron transport chain. This is, just, a beautiful thing. Really. We're still

  • in the mitochondria, and we do require oxygen for this step. This is a very complicated

  • process, and we are greatly simplifying it by saying that electrons are transferred from

  • the NADH and FADH2 to several electron carriers. They are used to create a proton gradient.

  • The protons are used to power an amazing enzyme called ATP synthase. Remember that the word synthase

  • means tomakeso that's what ATP synthase does. All the time. It makes the ATP by adding

  • phosphates to ADP. Oxygen is the final acceptor of the electrons. When oxygen combines with

  • two protons, you get H20---aka

  • water. The electron transport chain produces a lot of ATP compared to the other two steps.

  • There isn't an exact number on this---many textbooks will say 34 ATP. Meaning that the

  • net amount of ATP made when you add all the steps together is 38 ATP. But you need to

  • understand that this is a “perfect casescenario and in general, you can expect a

  • lot less ATP made.

  • If we look at our formula again, we can see how the glucose and oxygen on the reactant

  • side was used to produce carbon dioxide (a waste product), water (a waste product), and

  • ATP energy. ATP energy was our goal.

  • Now, this was just one way of creating ATP energy---and a very efficient way at that.

  • But like we had said at the beginning, all cells have to make ATP energy. But the way

  • that they do it can differ. If there is no oxygen available, some cells have the ability

  • to perform a process known as fermentation. It is not nearly as efficient, but it can

  • still can make ATP when there isn't oxygen.

  • We really can't emphasize enough how important the process of making ATP energy is. If you

  • doubt how powerful it is, consider cyanide. This toxin is found in some rat poisons and

  • highly toxic. It works by blocking a step in the electron transport chain. Without being

  • able to continue the electron transport chain, cells cannot produce their ATP, and this poison

  • can be deadly in a very short timeframe.

  • There is also a demand for increased research on various mitochondrial disorders. Many mitochondrial

  • disorders can be deadly, because the role of the mitochondria in our body cells is so

  • essential for our ATP production. We are confident that the understanding of how to treat these

  • disorders will continue to improve as more people, like you, ask questions. Well that's

  • it for the amoeba sisters and we remind you to stay curious.

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B2 中高級 美國腔

細胞呼吸與強大的線粒體 (Cellular Respiration and the Mighty Mitochondria)

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    Amy.Lin 發佈於 2021 年 01 月 14 日