Binary fission

• Binary fission:


  The process by which prokaryotic organisms, like bacteria, divide and reproduce.

  
• Binary fission is not the same as mitosis or meiosis, as these happen in eukaryotic cells.

  
• Bacteria are prokaryotic and unicellular:


  • When they divide by binary fission, they're also reproducing as each new cell is a separate organism.
  • It’s an example of asexual reproduction.

  
• Before a bacterial cell can divide:

  1. It has to grow a bit.

  • so it’s big enough to make two new cells.

  1. It has to replicate its genetic material:

  • its nucleoid
  • All of its little plasmids
  • so that there’s enough for each new cell.

  
• Stages of binary fission:

  • The two circular strands of DNA move to opposite sides of the cell.
  • So the offspring cells will end up getting one each.
  • But the plasmids are randomly arranged.
  • so there’s often more plasmids in one offspring cell than the other. 
  • Once the cell is ready to divide, A new cell wall form down the middle of the cell.
  • To allow The two halves to pull apart to form two daughter cells.

  
• Binary fission doesn’t take very long:

  • With the right conditions, one bacteria can divide once every 20 minutes.
  • As the population doubles with every division, the population grows quickly.

  
• Mean division time:


  It's the mean (average) time it takes for a bacterial cell to divide.
• A bacterial cell has a mean division time of 30 minutes, how many cells would it produce after 3 hours?

  Divide the total time by the mean division time, to find how many division cycles there will be in the 3h:

  • 180 mins (3hr) / 30 mins = 6
  • The bacteria can do six rounds of division in 3hrs.

  How many cells that would make:

  • Take the original cell (one bacterial cell) and double it, 6 times =$2^6$= 64.

  There will be 64 bacterial cells, after 3 hrs
• Mean division time depends on the species and the conditions.

  Bacteria require for optimal growth:

  • Moist
  • Plenty of nutrients
  • Warmth

  Without these, the bacteria will divide more slowly or not at all.

  
• A petri dish contains 1000 bacteria, each cell divides once every 20 minutes.

  How many cells will there be after 4 hrs?

  • 240 mins / 20 mins = 12 division cycles 
  • 1000 x 2^12 = 4,096,000 bacterial cells.

  
• A type of bacteria have a division time of 20 minutes.

  If the population starts with just one cell, how many bacteria cells would be there after 1h?

  8
• A type of bacteria have a division time of 30 minutes. If the population starts with 100 cells, how many bacteria cells would be there after 4h?

  25600
• Meiosis:


  Produces cells that are genetically unique from the parent and contain only half as much DNA.

  • While Mitosis produces two genetically identical “daughter” cells from a single “parent” cell.