What is a Eukaryotic 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.

Prokaryotes Eukaryotes Mitochondria Chloroplasts
DNA 1 single, circular chromosome Multiple Linear Chromosomes 1 single, circular chromosome 1 single, circular chromosome
Replication Binary Fission Mitosis Binary Fission Binary Fission
Ribosomes 70 S 80 S 70 S 70 S
Electron Transport Chain Found in plasma membrane around cell Not found in the plasma membrane around cell Found in plasma membrane around mitochondrion Found 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
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