Structure of an Epithelial Cell

Plasma Membrane


  • Regulates movement of substances in and out of cell
  • Receptor molecules that respond to chemicals.
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  • Folds in the plasma membrane
  • ↑ SA of surface area= ↑ rate of absorption (mainly found in epithelial cells of the S.intestines.


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  • Nuclear envelope that surrounds the nucleus. It contains nuclear pores- allows the passage of large molecules e.g. mRNA.
  • Nucleoplasm- granular, jelly like material that makes up the bulk of the nucleus.
  • Chromatin- DNA found in the nucleoplasm- diffuse form that chromosomes take up when the cell isn't dividing.
  • Nucleolus- spherical body- makes ribosomal RNA and assembles ribosomes.
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The Mitochrondion

  • Double membrane- outer controls entry and exit of material; inner folded to form cristae.
  • Cristae- provide a  large SA for attachment of enzymes during respiration.
  • Matrix- semi-rigid material containing proteins, lipids and traces of DNA- allows it to control the production of its own proteins.
  • Site of respiration so produces ATP; ↑ level of metabolic activity= ↑ in number and size of mitochondria.


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  • ribosomes present
  • provides large SA for synthesis of proteins and glycoproteins
  • provides pathway for the transport of materials throughout the cells.


  • no ribosomes
  • synthesizes, store and transports lipids and carbohydrates.


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Golgi Apparatus

  • modifies proteins; adding non-protein components to them.
  • transported in vesicles, move to the cell surface membrane, fuse to the membrane and release contents to the outside (exocytosis).
  • produces secretory enzymes
  • secretes carbohydrates
  • transports, modifies and stores lipids
  • forms lysosomes.


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  • formed when the GA's vesicles contain enzymes.
  • isolate the enzymes from the rest of the cell before releasing them to the outside or into a phagocytic vesicles within the cell.
  • breaks down material ingested by phagocytic cells.
  • digest worn out organelles.
  • breaks down cells after they've died.
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80S type- found in eukaryotic cells

70S type- found in prokaryotic cells (slightly smaller than 80S type)

  • two subunits- containing ribosomal RNA and protein.
  • protein synthesis
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