Binary Fission - The Prokaryotic Cell Cycle

• Prokaryotes

  • Bacteria and archaea are prokaryotes. Their cell cycle is through binary fission. lacks nucleus and membrane-bound organelles
  • Bacteria reproduce very very fast (through binary fission). some can divide about every 20 minutes. exponential growth
• Binary Fission

  • Most prokaryotes reproduce by binary fission, a relatively simple process by which one parent cell gives rise to two identical daughter cells. Asexual reproduction
  • Replication of DNA
  • Attachment
  • Cell Elongation
  • Z-ring formation and constriction
  • Septum formation and cytokinesis
• Replication of DNA

  • Prokaryotes contain one singular circular chromosome, contained within a nucleoid.
  • The origin of replication (oriC) is the point of a circular chromosome at which the helicase, primase and DNA polymerase III assemble into a replisome.
  • replication then proceeds in both directions toward the terminus (a point of a circular chromosome opposite oriC). By that time, we'll have two separate chromosomes.
  • basically, the chromosome uncoils and duplicates

  Thus, DNA replication is completed.
• Attachment


  Next, the chromsomes attach themselves to the cell membrane in different parts of the cell.
• Cell Elongation

  After attaching, the cell grows longer (elongates) to around twice the normal length of a bacteria.

  new cell wall material is being laid down
• Z-ring formation and constriction

  • After elongation is the Z-ring formation.
  • It is made from protein fibres. similar to the protein fibres in the cytoskeleton and spindle fibres. also the Z-ring forms in the centre of the bacterium from a protein called FtsZ.
  • The ring can wind itself, and become tighter and tighter in a process called constriction.

  As it tightens, the cell membrane and wall get drawn in and pinches together. like a ziptie.
• Septum formation and cytokinesis

  • The Z-ring co-opts a number of other proteins that synthesise a new cell wall called a septum, along the equator of the cell. Process called septum formation.
  • After formation of the septum, the cell wall is cut down the middle - cytokinesis. 2 separate cells.