Binary Fission

• Prokaryotic cells replicate by binary fission
• 1. The circular DNA and plasmid(s) replicate
• 2. The cell gets bigger and the circular DNA strands move to opposite 'poles' (ends) of the cell
• 3. The cytoplasm begins to divide and new cell walls begin to form
• 4. The cytoplasm divides and 2 daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)
• Bacteria cann divide very quickly if given the right conditions (e.g. a warm environment and lots of nutrients)
• Some bacteria such as E. coli, can take as little as 20 minutes to replicate in the right environment
• If conditions become unfavourable, the cells will stop dividing and eventually begin to die
• Use mean division time to find the number of bacteria in a population
• The mean division time is just the average amount of time it takes for one bacterial cell to divide into 2
• If you know the mean division time of a cell, you can work out how many times it has divided in a certain amount of time, and so the number of cells it has produced in that time
• Each cell divides to produce 2 daughter cells, so the number of cells increases by a power of 2 for each division
• A bacterial cell has a mean division time of 30 minutes. How many cells will it have produced after 2.5 hours?

  2.5 hours x 60 = 150 minutes. 150 minutes / 30 minutes = 5 divisions. 2^5 = 2x2x2x2x2 = 32 cells