Prokaryotic and Eukaryotic Cells
Living organisms are made of either prokaryotic or eukaroytic cells - two major kinds of cells, which can be distinguished by structural organization.
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Cytoplasm - Entire region between the nucleus and cell membrane.
Cytosol - Semi-fluid medium found in the cytoplasm.
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Cell Size Limitations
Size ranges of cells:
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Range of cell size is limited by metabolic requirements (the energy and chemical reactions needed to sustain life). The lower the limits are probably determined by the smallest size with:
  • Enough DNA to program metabolism
  • Enough ribosomes, enzymes and cellular components to sustain life and reproduce.
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The upper limits of size are imposed by the surface area to volume ration. As a cell increases in size, its volume grows proportionately more than its surface area.
  • The surface area of the plasma membrane must be large enough for the cell volume, in order to provide an adequate exchange surface for oxygen, nutrients and wastes.
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Advantages of Compartmental Organization
The largest eukaryotic cell has a thousand times the volume of the smallest prokaryotic cell, but only a hundred times the surface area. Eukaryotic cells compensate for the small surface area to volume ration by having internal membranes which:
  • Partition the cell into compartments.
  • Have unique lipid and protein compositions depending upon their specific functions.
  • May participate in metabolic reactions since many enzymes are incorporated directly into the membrane.
  • Provide localized environmental conditions necessary for specific metabolic processes.
  • Sequester reaction, so they may occur without interference from incompatible metabolic processes elsewhere in the cell.