Prokaryotic Growth & Reproduction

Phase of Growth in a Bacterial Culture

Phase 1: Lag phase

• It takes the cells a while to get accustomed to their environment before they can start dividing.
• The cells are in a non-growing shock phase.
• No change in population size.

Phase 2: Exponential Phase

• Active growth. Every cell is dividing.
• There is sufficient nutrients available to support division by all cells.
• Number of dividing cells outnumber the dying cells significantly.
• Population size increases exponentially.

Phase 3: Stationary phase

• Nutrients are just enough to support some growth.
• Dividing cells are equal to dying cells.
• Population size is not changing.

Phase 4: Death phase

• Nutrients are depleted. Waste product accumulation becomes toxic.
• More dying cells than newly dividing cells.
• Population is declining.

Binary Fission: Prokaryotic Cytokinesis

• Occurs mainly in single-celled organisms.
• All genetic material in the cell is replicated before cytokinesis (bacteria have extrachromosomal DNA like plasmids that are also replicated).
• When DNA is replicated, the origins (Ori site) are attached to the poles of the cells by the partitioning proteins ParA/ParB. This enables chromosomal segregation.
• Cytokinesis:
• Constriction of cells into two daughter cells is done by a cytoskeletal protein know as FtsZ.
• FtsZ proteins form a ring at the constriction site.
• The ring contracts to pinch the two cells apart.