Cellular Respiration and the Mighty Mitochondria


Closed captioning is on. To turn off, click the CC button at bottom right. Follow us on Twitter (@amoebasisters) and Facebook! 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 to “make” so 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 case”
scenario 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.