Imagine for a moment that one of your siblings needs a new kidney. If you don't have any siblings, pretend you do, or use your imaginary friend Drop Dead Fred. Often, when something like this happens, people end up waiting for months or even years for a kidney to become available. Many even die before an organ donor is found. Wouldn’t it be wonderful if doctors could simply take a few of your sibling’s healthy kidney cells and grow a whole new kidney in the lab?
In the past few decades, biologists have been trying to figure out how to do this very thing. One solution they have found is a process called therapeutic cloning, where a nucleus from a patient’s somatic cell, or any cell in the body that is not an egg or sperm cell, is inserted into a special fertilized egg cell. This egg cell is special because all of its DNA, including its nucleus, has been removed before fertilization, meaning that only DNA from the patient is present after somatic cell nucleus insertion. At this point, the combined cells are allowed to grow and divide until they form a small mass of cells called a blastocyst, which contains stem cells.
The blastocyst, in all its glory:
Biologists can remove these stem cells and grow them into almost any tissue in the body, including, potentially, a kidney. Even though this seems like the perfect solution to a very worrisome problem, it’s not all peaches and blastocysts. Many people strongly object to therapeutic cloning because they believe that life begins at the moment an egg cell is fertilized. To them, the blastocyst from which stem cells are taken is a form of human life and should not be harmed. Even for those who do not believe that life begins at conception, there are major concerns about how available such a procedure would be to the general public, or even if there might be serious problems that would appear years after a cloned organ had been transplanted.
Because of these concerns, research on therapeutic cloning has not proceeded very far, and most of the benefits it might provide for humans are only theoretical at this point. However, interesting studies on mice and other organisms have shown that therapeutic cloning in humans, if allowed, would most likely be quite beneficial. If you have an opinion on this important ethical issue in cell biology, we at Shmoop would love to hear it.
One last bit about mitochondria (we promise!). In addition to making ATP so that our cells can function, mitochondria also let off a lot of heat. Most of the energy from that molecule of glucose—60% in fact—is lost as heat. Before you start thinking, "What a waste of energy!" (we caught you thinking it, didn’t we?), keep in mind that most combustion engines are only 18-20% efficient, meaning 80-82% of the energy from every molecule of gasoline is lost as heat! Yeah, what is that you were saying about your mitochondria wasting energy?
In reality, the fact that mitochondria are only 40% energy-efficient is a really good thing. In fact, it’s vital to life. We find ourselves saying that a lot. The heat produced by mitochondria during cellular respiration is actually harnessed by the cells of our bodies and used to regulate our internal temperatures. The ability to harness heat from cellular respiration is a trademark characteristic of endothermic animals. The term "warm-blooded" is often used to describe endothermic organisms, but it is an inaccurate term. Blood cells do not have mitochondria and cannot, therefore, produce heat. They should be called "warm-mitochondriad" animals instead. As if that will happen.
During infection, our body’s temperature regulation system captures more heat than usual, and we experience the sensation of a fever. If too much heat is retained so that the core body temperature rises above 108 °F, the regulatory system breaks down, and the heat from our mitochondria quickly kills our cells. Eek. When this happens, we experience the uncomfortable sensation of…death. On the flip side, if the environment outside our cells gets too cold, especially in freezing water, our mitochondria have a hard time producing enough heat to bring our core temperature back up to our normal 98.6 °F. If this condition lasts for too long, we experience hypothermia and, eventually…death. Apologies for the bluntness. Therefore, in addition to providing our cells with the energy they need to grow and reproduce, mitochondria play a vital role in maintaining the internal temperature our cells need to survive.
Every year around the world, billions of dollars' worth of crops are damaged by tiny little roundworms called nematodes. This cell wall degradation allows for syncytia to form and for nematode infection to proceed more quickly. This is bad, bad, bad for the plant.
While a few nematodes might not do any noticeable damage to a plant, if too many syncytia are formed, plant growth can suffer dramatically. It’s the accumulated effect of trillions of nematodes hijacking trillions of plant cells that causes such incredible crop loss worldwide—and it all happens at the cellular level!