prokaryotic cells

• • Cells differ in a number of ways, but a key difference is the presence of a nucleus.
  • Prokaryotic cells have no nucleus. 'Pro' meaning 'before' and 'karyon' meaning 'nucleus'.
  • Eukaryotic cells do have a nucleus. 'Eu' means 'true' and 'karyon' means 'nucleus'.
• Prokaryotes contain few organelles and none are surrounded by a plasma membrane such as the nucleus, mitochondria and chloroplasts in eukaryotes.
• Genetic material

  • The genetic information is not stored in a nuclear envelope, instead a single large circular chromosome is free in a special region of the cytoplasm. This is called the nucleoid.
  • There may be copies of the genes on plasmids loose in the cytoplasm.
• Protein synthesis

  • In eukaryote cells this is carried out by larger ribosomes (80S) which may be attached to the endoplasmic reticulum (ER).
  • In prokaryotes the ribosomes are far smaller (70S) and are not attached to ER.
• Respiration

  In bacteria, respiration occurs in mesosomes (infolds of the cell membrane), though it occurs in cytoplasmic membranes in blue-green bacteria as opposed to in mitochondria in eukaryotes.
• Cell walls

  • In prokaryotes these are rigid and contain polysaccharides with amino acids. A substance called murein - which is a polysaccharide cross linked with amino acids (peptidoglycan)  - strengthens the wall.
  • In some bacteria this can be coated with a lipopolysaccharide which offers extra protection.
• Due to the fact that prokaryotes are either unicellular or filamentous in shape, they require a means of mobility.

  Many bacteria are motile due to the presence of one or more flagella, though these are far simpler than those found in eukaryotes.

  They do not beat, but instead perform corkscrew motion to propel the cell along.
• The capsule of a bacterium will show up very clearly when the slide is negatively stained (the background, rather that the object is stained).

  The capsule (and slime) layers are secretions of certain bacteria.

  A capsule is relatively thick and compact and is attached firmly, whereas a slime layer is diffuse and attached loosely. It is found on the outside of the cell wall. They can be known as the glycocalyx.

  Both of extra protection to the bacterial cell.