Binary Fission

Binary fission is an asexual way to reproduce. The single living cell or organelle doubles in size before splitting into two identical daughter cells. Thereafter, each of which has the potential to expand to the size of the original cell or organelle.

Binary fission differs from other forms of fission. It is capable of producing only two components from a single entity.

This process does not involve the formation or fusion of gametes, hence it is referred to as asexual reproduction.

In this asexual method of reproduction, the daughter cells produced have the same genetic material as their parents.

Many prokaryotes, including archaea, cyanobacteria, eubacteria, and certain eukaryotes like amoeba and Paramecium, reproduce by binary fission.

Binary fission occurs in some cell organelles, like mitochondria. It must be able to reproduce at the right time, in the right place, and give each offspring a complete copy of its important genetic material to stay alive and compete.

Types and Examples

Binary fission has four forms based on the cytoplasmic division plane.

• Irregular Binary Fission

Cytoplasm division (cytokinesis) can occur in any plane in this situation. It is most typically perpendicular to the plane of chromosome division (karyokinesis).

This type can be found in organisms such as amoebas.

• Transverse Binary Fission

Cytokinesis occurs along the cell's transverse axis in transverse binary fission.

This division can be seen in Paramecium, a ciliated protozoan. This is where the cytoplasm is separated along the cell's longitudinal axis.

• Longitudinal Binary Fission

This is where the cell's cytoplasm is separated longitudinally.

This method of division generally occurs in Flagellates, such as Euglena.

• Oblique Binary Fission

In this case, the cytoplasm is separated in an oblique manner (i.e. left and right oblique).

Ceratium, a dinoflagellate, has this division pattern.

Examples

Prokaryotes and eukaryotes also use binary fission as a means of dividing into smaller units.

The FtsZ protein is involved in 

• The chromosomal replication

• Chromosomal segregation

• Cell splitting processes

This process leads to the reproduction of most of the bacteria.

There are few protozoans in which the process of cell division and cytoplasmic division may differ. Eg. Amoeba, Paramecium, and Euglena.

There are below organisms that are reproduced by binary fission:

• Bacillus subtilis

• Bacillus cereus

• Bacillus pumilus

• Escherichia coli

• Clostridium perfringens

• Corynebacterium diphtheriae

• Amoeba

• Paramecium

• Euglena

• Ceratium

Binary Fission in Prokaryotes

• Prokaryotes' genetic material (chromosomes) is contained as a nucleoid in the cytoplasm.

• The chromosomes are then replicated starting at the origin of replication. Later, the origin divides, and as the replication continues, the two origins pull the chromosomes with them.

• After replication, proteins involved in cell division gather at the center of the cell.

• The FtsZ protein, which forms a ring-like structure in the cell's core, is vital in this process.

• This step ensures that the cytoplasm separates without damaging the genetic material.

• The membrane pinches inwards, generating a septum (new cell wall) down the cell's center.

• Finally, the septum splits into two cells, each with its own identity.

• Crenarchaeota, which lacks a cell wall and the FstZ protein, uses a primitive mechanism called the ESCRT-III system.

Binary Fission in Eukaryotes

• Some protozoans, such as amoebas, reproduce by binary fission, and some organelles within eukaryotic cells divide similarly to bacteria.

• The FtsZ protein is involved in binary fission in these cells, as in prokaryotes.

• The Endosymbiotic theory, which explains how prokaryotes evolved into today's mitochondria, is based on the binary fission of cell organelles such as mitochondria and chloroplasts.

Binary Fission in Bacteria

Bacteria also reproduce through asexual reproduction and the speed differs between species. The time taken for one bacterial cell to duplicate itself is called doubling time.  Factors such as pH levels, temperature, light, oxygen, osmotic pressure play a factor in bacterial reproduction or bacterial binary fission. The following are the steps involved in the binary fission of bacteria.

• Genome Replication: In bacteria, binary fission starts with the replication of the genome. Replication enzymes copy the chromosome strand at the point of origin and then continue separating the strand in two. 

• The Growth of the Cell: After the chromosome is duplicated in two strands, the bacterial cell grows larger and prepares for binary fission. The volume of cytoplasm and cell organelles increases with the cell. Another feature of this stage is that the two chromosome strands migrate to opposite poles of the cell.

• The Segregation of the Genetic Material: In this stage, the plasma membrane’s peripheral ring invaginates and divides the mother cell into two. It is accompanied by the formation of a double membranous septum before two cells completely separate into two identical cells.  

• Splitting into Two Cells: This stage starts with the development of a cell wall and the cell splits at the center.  Afterward, the mother cell divides into two daughter cells. Each daughter cell contains one copy of the genetic material and all necessary cell organelles.