Learning Objectives It is thought that life arose on earth around four billion years ago. The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and 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 chloroplasts cannot grow outside their host cell. Evidence for this is based on the following:
Although evidence is less convincing, it is also possible that flagella and cilia may have come from spirochetes. Figure \(\PageIndex{1}\): One model for the origin of mitochondria and plastids. This model has an amitochondriate eukaryote engulfing an aerobe and then a cyanobacterium. from KelvinsongExample \(\PageIndex{1}\)
Solutions
SummaryThe endosymbiotic theory states that mitochondria and chlopoplasts in today's eukaryotic cells were once separate prokaryotic microbes. How do mitochondria support the endosymbiotic theory?The endosymbiotic hypothesis for the origin of mitochondria (and chloroplasts) suggests that mitochondria are descended from specialized bacteria (probably purple nonsulfur bacteria) that somehow survived endocytosis by another species of prokaryote or some other cell type, and became incorporated into the cytoplasm.
Which of the following characteristics of mitochondria and chloroplast does not support endosymbiotic theory?Mandira P. Martin M. "The exterior structure similar to bacterial cell walls" IS NOT an evidence in favour of the endosymbiotic theory. Both mitochondria and chloroplasts are double membrane bound.
How do mitochondria and chloroplasts show evidence of endosymbiosis?The ribosomes of mitochondria and chloroplasts also resemble the smaller ribosomes of bacteria, and not the large eukaryotic ribosomes. This is more evidence that the DNA originated inside of the organelles, and is separate completely from the eukaryotic DNA. This is consistent with endosymbiotic theory.
What are the 3 pieces of evidence that support the endosymbiotic theory?10 Best Evidence of Endosymbiotic Theory. i) Presence of DNA:. ii) Size of Ribosomes:. iii) Inhibition by antibiotics:. iv) Evolutionary relationship:. v) Same size:. vi) Plasma-Membrane:. vii) Enzyme secretion:. viii) Replication and protein synthesis:. |