1 month, 2 weeks ago

 
 about the origin of mitochondria, the most representative one is 
 endosymbiotic theory 
. 



 1. Swallow and spit out 


To survive, single celled organisms need to take in materials and energy. Like "big fish eat small fish, small fish eat shrimp", big cells also want to swallow small cells. This process is called endocytosis. The process of endocytosis is closely related to the fluidity of cell membrane. What is swallowed will be wrapped with a layer of cell membrane and enter into the cell interior. The cell will carry out a series of operations to decompose and utilize it and spit it out of the cell. The process of spitting out is called exocytosis 
 [1] 
. 


? 

If the small cell is swallowed but not digested, but symbiotic in the large cell, this is called endosymbiosis. 


 2. Swallowing, pay attention to safety. 


In short, about one billion years ago, a large, phagocytic Archaea (archaeokaryon cells) swallowed an aerobic, smaller, archaeokaryon (aerobic eubacteria, such as proteobacterum) 
 [2] 
. 

Swallowing is a problem, but pay attention to safety. It's not good to kill the swallowed creatures. Archaeokaryotes may have a series of stress changes to protect themselves. For example, a large number of invaginations of the cell membrane form a primitive endoplasmic reticulum system, thus limiting the activity of the swallowed bacteria. The primitive endoplasmic reticulum system is further specialized, and the genetic material of the cell is wrapped to form the nucleus. Archaeokaryotes became archaeoeukaryotes. 




Some of the ingested aerobic bacteria are not only undigested and undigested, but also gradually survive in the large, ancestral cells. 


. And the progenitor cell phase can also accept, which is when a pet is raised. Although it needs to be wrapped up, it can get the energy and products of glycolysis from aerobic bacteria, which is not a loss. As a result, the two organisms form an interdependent symbiont, which is beneficial to both sides. In this way, in the long-term evolution process, the ingested organisms transited from parasitism to symbiosis, and finally formed mitochondria. 


 4. Swallow and leave evidence 


The evidence supporting the above theory is mainly due to the comparison of 
 mitochondria and eubacteria 
. It is found that they are similar in many places. 
The size of 
 
 was similar. 

They proliferate in a dichotomous manner. 

It has similar covalent, closed, circular DNA. 

The size and structure of ribosome are similar, and the sedimentation coefficient is the same. 

Protein synthesis can be inhibited by antibiotics. 
In addition, endosymbiosis theory can also explain why mitochondria are bilayer membrane, but unlike most people think, bilayer membrane may come from bacteria 
 [3] 
. 




Fortunately, mitochondria are the problem, because it's more difficult to explain chloroplasts. 

The origin of chloroplast is similar, except that the original photosynthetic prokaryote (such as cyanobacterium) is swallowed, which produces green algae and red algae. The early green algae and red algae were once again swallowed and evolved into chloroplasts. 

A large number of photosynthetic autotrophic protozoa, such as diatom, brown algae, Euglena, dinoflagellate and so on, are all originated from this second endosymbiosis. 


. Below is a Chinese translation. 




To sum up, if only one word is used to answer how mitochondria come from, it is - "
 swallow 
.". 

Ha ha ha ha, this is a good question!

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