Prokaryotic and eukaryotic cells

• Prokaryotic cells


  Cells without a nucleus or membrane-bound organelles
• Eukaryotic cells


  Cells with a nucleus and membrane-bound organelles
• Differences between prokaryotic and eukaryotic cells

  • Internal compartmentalisation afforded by complex endo-membrane system of eukaryotes
  • Presence of a nucleus and dense-staining chromatin (DNA-protein complexes) within it
  • Complex cytoskeleton of filamentous proteins found in eukaryotes
• DNA in prokaryotes undergoes folding but is not bound to protein as in nucleosomal subunits of eukaryotic chromatin
• Prokaryotic DNA is located in the nucleoid, a morphologically distinct region of cytoplasm, but which lacks a limiting membrane
• Prokaryotic cell


  • Periplasmic space and cell wall
• Eukaryotic cell


  • Nucleus
  • Golgi vesicles
  • Lysosome
• Cell Ultrastructure


  • Correlates closely with their differentiated function. Cells differentiate to allow them to carry out specific functions
• Chromatin pattern


  • Reflects transcriptional activity
• Concentration of polyribosomes in cytoplasm

  • Closely aligns with translational activity
• Disposition of polysomes


  • Indicates whether proteins under translation are destined for internal use or export
• Free polysomes


  Tend to produce proteins for internal use
• Polysomes attached to rough endoplasmic reticulum


  Tend to produce proteins for export
• Proteins for internal use that require membrane packaging


  Follow the secretory pathway until the penultimate step
• Mitochondria


  • Major source of ATP
  • Closely apposed to sites of ATP usage, such as plasma membranes with high ion pumping demands (eg dct and pct in the kidney)
• Transporting epithelial cells (e.g. proximal convoluted tubules of kidney)


  • Baso-lateral surface has high ion pumping demands
• compare euchromatin and heterochromatin and give an example cell type for each


  • Euchromatin is finely dispersed seen in myofibroblasts and contrasts with densely-stained heterochromatin (HC) of adjacent melanocytes
• Myofibroblasts


  • Extensive rough endoplasmic reticulum and prominent Golgi apparatus for bulk production of matrix proteins for export
• Distal convoluted tubule


  • Deep infolding of the baso-lateral plasma membrane facilitates close apposition of the ATP-dependant ion pumps of the plasma membrane with the source of ATP in the mitochondria
• Endomembrane System of Eukaryotic Cells


  • Composed of different membranes suspended in the cytoplasm which divide the cell into functional and structural compartments (organelles)
  • Includes: Nuclear envelope, Endoplasmic reticulum, Golgi apparatus, Lysosomes, Vacuoles, Vesicles
• Components of the Endomembrane System


  • Nuclear envelope
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
  • Vacuoles
  • Vesicles
• The endomembrane system does not include the membranes of mitochondria