Microbiology, part 15: Prokaryotes & Eukaryotes - Endosymbiotic Theory

Hi. I'm Cathy with Level Up RN. In this video, I will be discussing the endosymbiotic theory. And at the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key points I'll be covering, so definitely stay tuned till the end of the video. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on endosymbiotic theory so you can follow along with me.

The endosymbiotic theory explains how certain organelles, in particular mitochondria and chloroplasts, evolved from prokaryotic cells. The mitochondrion is an organelle in a eukaryotic cell where aerobic cellular respiration occurs. The endosymbiotic theory states that this organelle originally arose when a bacterium capable of aerobic cellular respiration was taken into a eukaryotic cell via phagocytosis and then remained in the cell as an intracellular component. This theory also applies to chloroplasts, which are organelles found in some eukaryotic cells, such as plant cells and algae cells. The chloroplast is where photosynthesis occurs. And the endosymbiotic theory states that this organelle originally arose when a bacterium capable of photosynthesis was taken into a eukaryotic cell via phagocytosis and then remained in that cell as an intracellular component.

There are several key pieces of evidence that support endosymbiotic theory. First of all, the DNA in mitochondria and chloroplasts is circular, which is the same as prokaryotic or bacterial cells, but is different than eukaryotic cells, which contain DNA in linear chromosomes. The next piece of evidence is the fact that the ribosomes found in mitochondria and chloroplasts are 70S ribosomes, which is the same as prokaryotic ribosomes, but is different than eukaryotic ribosomes, which are 80S ribosomes. Mitochondria and chloroplasts are small in size, just like prokaryotic cells, whereas eukaryotic cells are larger in size. Mitochondria and chloroplasts divide by binary fission, just like prokaryotes, whereas eukaryotic cells divide by mitosis.

And finally, mitochondria and chloroplasts have a double membrane, and the composition of the inner membrane is similar to the composition of a prokaryotic plasma membrane, whereas the composition of the outer membrane is more similar to a eukaryotic plasma membrane, which suggests that when the bacterium was taken up via phagocytosis, the host cell's plasma membrane wrapped around the bacterium, and this became the outer membrane of the organelle.

All right. It's quiz time, and I have three questions for you. Question number one, the presence of which two organelles in a eukaryotic cell can be explained by the endosymbiotic theory? The answer is, mitochondria and chloroplasts. Number two, how do the ribosomes in a chloroplast support endosymbiotic theory? The answer is, the ribosomes in a chloroplast are 70S ribosomes, which are the same as the ribosomes found in a prokaryotic cell. Question number three, the inner membrane of a mitochondrion is similar in composition to the plasma membrane of a eukaryotic cell. True or false? The answer is, false. It is similar in composition to the plasma membrane of a prokaryotic cell.

All right. That's it for this video. I hope it was helpful. Thank you so much for watching, and good luck with studying.