The Prokaryotic Cell Cycle

 Cell cycle 

The sequence of events by which a cell duplicates it's genome, synthesis the other constituents of the and eventually divides into two daughter cells is termed cell cycle. Most prokaryotes reproduce by binary fission, although some prokaryotes reproduce by budding, fragmentation, etc.

Prokaryotic cell cycle is the process by which prokaryotic cell ( like bacteria & archaea) grow and division. Unlike eukaryotic cells, which have a complex, multi-phase cell cycle (G1,S,G2,M), prokaryotic haves a simpler cycle due to their lack of a nucleus and fewer organelles. No spindle formation, no mitotic phase, DNA is a single circular chromosome located in the cytoplasm.

Binary fission is a relatively simple type of cell division: the cell elongates, replicates its 

chromosome, and separates the newly formed DNA molecules so there is one chromosome in each half of the cell. Finally, a septum (or cross wall) is formed at mid cell, dividing the parent cell into two progeny cells, each having its own chromosome and a complement of other cellular constituents. 

Stages of the Prokaryotic cell cycle 

1. Cell Growth ( B period )

• The cell increases in size.
• Nutrient are absorbed from the environment.
• The cell prepares for DNA replication.

2. DNA Replication ( initiation phase )

• The single, circular chromosome is duplicated.
• Replication starts at a specific site called the origin of reply ( ori ).
• The DNA opens up and forms two replication forks.

3. DNA Segregation ( Partitioning )

• Replication is completed at the terminus, which is located directly opposite the origin.
• The origin and terminus move to mid cell and a group of proteins needed for DNA synthesis assemble to from the replisome at the origin.

4. Cytokinesis 

• Septation is the process of forming a cross wall between two daughter cells.
• In bacteria like E. coli, cytokinesis is carried out with the help of Fts protein forming alpha Z- ring.

Proteins in involved in cytokinesis in Rod shaped bacteria :-

1. Mere B - The actin homolog Mre B forms spiral filaments around the inside of the cell that help determine cell shape and may serve to move chromosomes to opposite cell poles.
2. Fts Z - The tubulin-like protein Fts Z assembles in the centre of the cell to forms a Z- ring, which is essential for septation.
3. Z ring - once the Z ring forms, the rest of the division machinery is constructed. This machinery synthesizes the division septum, which consists of cell-wall material.
4. Min CD - together with other Min protein, oscillates from pole to pole, thereby preventing the formation of an off-center Z ring. Min CD is a inhibitor of Z ring.