Endosymbiotic Theory - Video Tutorials & Practice Problems
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Endosymbiotic Theory
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Video transcript
In this video we're going to begin our lesson on the Endosymbiotic Theory. And so the Endosymbiotic Theory is a theory that suggests that today's mitochondria and chloroplast organelles that can be found in many eukaryotic cells were actually once independently living bacteria. Now this would have been a very long time ago. In fact, the endosymbiotic theory suggests that about 1.5000000000 years ago there would have been an aerobic bacterium or a bacteria that utilizes oxygen in its metabolism that was engulfed by an anaerobic host cell or a host cell that does not utilize oxygen in its metabolism. And so when this aerobic bacterium was engulfed by the anaerobic host cell, it would have created a symbiotic relationship or a relationship between the 2 organisms where both organisms benefit. And so the aerobic bacterium would have benefited from this engulfment by being provided extra protection. And the anaerobic host cell would have benefited from the engulfment by acquiring a metabolism that utilizes oxygen. And so over time, after engulfing the aerobic bacterium, the aerobic bacterium would have altered and lost many of its genes and abilities. And again, over an extremely long period of time, 1000000000 of years, it would have developed into today's Mitochondria. Which we know that the Mitochondria is an organelle found in eukaryotic cells. And so the mitochondria today is not considered a bacteria. However, again, the endosymbiotic theory suggests that the mitochondria would have once been an independently living aerobic bacteria. Now, in a very similar way, a photosynthetic cyanobacterium or in other words a bacterium that is capable of performing photosynthesis would have been engulfed by the host cell as well. And again, over an extremely long period of time, 1000000000 of years, the Photosynthetic Cyanobacterium would have evolved into today's Chloroplast organelles that are found in many plant cells. And so if we take a look at our image down below, we can clarify this idea of the endosymbiotic theory. And so what you'll notice is on the far left hand side we're showing you a host cell that is an anaerobic host cell that does not utilize oxygen in its metabolism and we're also showing you an aerobic bacterium over here that does utilize oxygen in its metabolism. And notice that this aerobic bacterium is independently living so it survives without the host cell. However, again about 1,500,000,000 years ago this aerobic bacterium would have been engulfed by this host cell. And so you can see the engulfment process beginning here and over here it is completely engulfed. And so again, over 1000000000 of years, this aerobic bacterium that was engulfed by the host cell would have altered many of its genes and lost many of its abilities and it would have developed into today's mitochondria organelle. And so we can label this as the mitochondria. And so, the development of the mitochondria ultimately allowed for complex organisms to arise, and complex animals to arise and that's how we ended up getting these cute little monkeys like what you see here and other animals as well. And so, notice if we go back up to our image, there is another, prokaryotic cell here, a cyanobacterium that is photosynthetic that would have also been engulfed in a similar way. And so, a host cell that would have engulfed both the Cyanobacterium and the aerobic bacterium would have become a plant cell. And again, the cyanobacterium would have evolved over an extremely long period of time, lost and changed many of its genes and abilities to become today's chloroplast. And so once again, cells that had both the Chloroplasts and the mitochondria would have developed into today's plant cells and, recall that plant cells have both chloroplasts as you can see here in this image, these little green structures, but they also have mitochondria as well and so that's important to keep in mind. Now again, this is an endo, this is the endosymbiotic theory and theories are supported by large bodies of evidence. And so some of the supporting evidence for the endosymbiotic theory includes these similarities between, today's mitochondria and chloroplasts and prokaryotic cells. And so what you'll notice here is we're listing out some of the similarities between today's mitochondria and Chloroplasts and prokaryotes. And so what you'll notice is that both, mitochondria and chloroplasts and prokaryotes have small circular DNA, they both have 70s ribosomes which is characteristic of prokaryotic cells and they both replicate via a process known as binary fission. And so, these are all similarities between the mitochondria and chloroplasts and prokaryotes and so that suggests that these mitochondria and chloroplasts may have been once prokaryotes that were independently living 1,000,000,000 of years ago. Now also in addition to this, mitochondria and chloroplasts both have 2 membranes. They both have an outer and an inner membrane. And so having an outer and an inner membrane is actually consistent with this idea of engulfment where it would have acquired its second membrane, the outer membrane, through the engulfment process. And so, again these are all ideas that are supporting, the Endosymbiotic Theory. And so this here concludes our brief lesson on the Endosymbiotic theory and how it suggests that today's mitochondria and chloroplasts were once independently living bacteria billions of years ago. And so I'll see you all in our next video where we can apply some of these concepts.
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Problem
Problem
Endosymbiotic theory is supported by the discovery of non-nuclear DNA in the ______ and ________ organelles.
A
Golgi apparatus and lysosomes.
B
Mitochondria and lysosomes.
C
Chloroplast and Golgi apparatus.
D
Chloroplast and mitochondria.
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Problem
Problem
According to the endosymbiotic theory, which of the following is likely the ancestor of the mitochondria?