11/10/15

This week the topic was on Endosymbiosis. Although I have learnt about mitochondria and chloroplast before, they were not as detail as mentioned in this topic. An American biologist proved that some organelles which are within cells were once free living cells. The examples given were mitochondria and chloroplast.

                                                                      Mitochondria

Endosymbiosis theory suggested that “Eukaryotes arose from a symbiotic relationship between various prokaryotes.”, “Heterotrophic bacteria became mitochondria while cyanobacteria became chloroplast.” and “The host cell of mitochondria as well as chloroplast was a large eukaryotic cell.”. I thought that the theories were true because the host cell couldn’t be smaller than mitochondria and chloroplast or else how did the host cell engulf the mitochondria and chloroplast.

                                                                   Cyanobacteria


Moreover,there are evidences that support the theories. For example, mitochondria and chloroplast have similar size and morphology as bacterial prokaryotic cells. Mitochondria and chloroplast are also divided by binary fission which are similar to bacteria and different to eukaryotes which divide through mitosis. They also have their own DNA and ribosomes with 30S and 50S subunits. They are also affected by antibiotics that used to kill bacterias. Anaerobic prokaryotes were formed 3.8 billion years ago while eukaryotes, mitochondria and chloroplast were formed 1.5 billion years ago. This showed the ancestor of mitochondria and chloroplast were prokaryotes because they need time to evolve from what they were to what they are now. Their ancestor couldn’t be eukaryotes as there wasn’t enough time for them to undergo evolution.

I think this topic is important to us because by the knowledge we gained in this topic we are able to differentiate whether a cell is from eukaryotes or prokaryotes. It could be very useful in the future when I’m doing research.