What is semiautonomous cell

 General Eukaryotic Cell Diagram

Features of a Eukaryotic Cell:

  • Nucleus (bound by a double membrane)
  • Membrane bound organelles
  • Can be both multicellular or unicellular
  • Cytoskeleton
  • Cilia
  • Linear DNA structure *
  • DNA organized into chromosomes*
  • Semiautonomous organelles (mitochondria & chloroplasts)*

The last three bulleted items above were starred to emphasize the importance that these features have to the Endosymbiotic Hypothesis.  Eukaryotic cell DNA has a linear orientation but this statement is referring to the DNA found in the nucleus of the cell. This DNA is complexed with proteins called histones and organized into chromosomes. In addition to this DNA, another form of DNA is also present. Semiautonomous organelles such as mitochondria and chloroplasts have DNA separate from that of the DNA found in the nucleus of eukaryotic cells. This has led to the belief that mitochondria and chloroplasts are descendants of independent cells that were engulfed by a larger anaerobic bacterium. Evidence for this theory has been gathered by comparing the features of prokaryotic cells with that of the semiautonomous organelles contained in eukaryotes. The similarities between these three have been organized into the following data table and compared to the features of eukaryotic cells.

ProkaryotesEukaryotesMitochondriaChloroplasts
DNA1 single, circular chromosomeMultiple Linear Chromosomes1 single, circular chromosome1 single, circular chromosome
ReplicationBinary FissionMitosisBinary FissionBinary Fission
Ribosomes70 S80 S70 S70 S
Electron Transport ChainFound in plasma membrane around cellNot found in the plasma membrane around cellFound in plasma membrane around mitochondrionFound in plasma membrane around chloroplast
Size~1-10 microns~50-500 microns~1-10 microns~1-10 microns
Appearance on Earth~3.8 Billion~1.5 Billion years ago~1.5 Billion Years ago~1.5 Billion Years ago