Answer to Question #125802 in Evolution for manal

Question

Endosymbiosis is the major theory that describes the evolution of eukaryotic cells from prokaryotic organisms. So, what is any other theories that used to account for this process and comment on which you think is the most probable.

Answer 1

The endosymbiotic theory states that some of the organelles in present eukaryotic cells were once prokaryotic microbes. in this theory, the first eukaryotic cell was probably an amoeba like cell which got nutrients by phagocytosis and contained a nucleus which formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. some of those amoeba like organisms ingested prokaryotic cells and survived within the organism hence developed a symbiotic relationship. mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. they eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell. mitochondria and chloroplast cannot grow outside their host cells.

Evidence of this is based on the following:

• Chloroplasts are the same size as prokaryotic cells, divide by binary fission, and like bacteria, have Fts proteins at their division plane. The mitochondria similar in size as the prokaryotic cells, divide by binary fission, and the mitochondria of some protists have Fts homo logs at their division plane.
• Mitochondria and chloroplasts have their own DNA that is circular, not linear.
• Several more primitive eukaryotic microbes, such as Girdia and Trichomonas have nuclear membrane but with no mitochondria.
• Mitochondria and chloroplasts have their own ribosomes that have 30S and 50S, not 40S and 60S.

The endosymbiotic theory that mitochondria and chloroplasts in eukaryotic cells today were once separate prokaryotic microbes holds the basis for the theory.