Prokaryotic & Eukaryotic Cells

• Prokaryotic cells

  • Prokaryotic cells are much smaller than eukaryotic cells (between 100 - 1000 times smaller) so normal microscopes aren't really powerful enough to look at their internal structure.
  • Prokaryotic cells also differ from eukaryotic cells in having:
  • A cytoplasm that lacks membrane-bound organelles
  • Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)
  • No nucleus (instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins)
  • A cell wall that contains murein (a glycoprotein)
• Prokaryotes vs Eukaryotes similarities

  -plasma membrane

  -cytoplasm

  -ribosome for assembling amino acids into proteins

  -DNA and RNA
• Prokaryotes vs Eukaryotes differences

  -DNA in nucleus in Eukaryotes

  -no nucleus in Prokaryotes

  -much less well-developed cytoskeleton with no centrioles in Prokaryotes

  Some prokaryotic cells also have:

  • a protective waxy capsule
  • small loops of DNA (plasmids)
  • flagella
  • pili

  
• Flagella


  -a long, tail like structure which rotates to move the cell(some prokaryotes have more than one)-not present in all prokaryotes

  • Found in specialised cells
  • Similar in structure to cilia, made of longer microtubules
  • microtubules contract to provide cell movement for example in sperm cells
• Plasmid


  
-small loops of DNA that are separate from the main circular DNA molecule-not present in all prokaryotes

  • Plasmids contain genes that can be passed between prokaryotes (e.g. genes for antibiotic resistance)
• Capsule


  -Some prokaryotes (e.g. bacteria) are surrounded by a final outer layer known as a capsule. This is sometimes called the slime capsule.-not present in all prokaryotes

  • It helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism
• Pili


  
-hair-like structures which attach to other cells or surfaces; involved in sexual reproduction