Prokaryote: Reproduction and Growth

Prokaryotes like bacteria divide and produce their daughter by the process of binary fission. It is one of the types of asexual reproduction, so in this method, the cell grows and divides and thus give rise to the new individual.

This method (binary fission) is followed by the unicellular organisms. However, transformation, transduction and conjugation are the other process by which they are able to exchange their genetic materials.

As we know that the single-celled organisms have very simple cellular structure and there is no well-defined nucleus and other organelles except few. Instead, their genetic information control centre is handled by the single loop of DNA. Although some of the bacteria also have an extra-chromosomal material known as a plasmid. This plasmid is advantageous in some or the other way to the bacteria, as it gives resistant to certain antibiotics.

Binary Fission

This is the most common method followed by the single-celled microbes. The DNA in the prokaryotes are present as a single-celled, circular chromosome. These organisms do not undergo meiosis, rather they simply divide into two equal and gets separated after their chromosomes get replicate and grow into the fullest.

Due to the simple cellular structure, their cell division is also less complexed and is a rapid process than the cellular division of the eukaryotes

Let us understand the simple steps:

  • Parent cell grows to the fullest size.
  • This is followed by the duplication of the chromosomes present in the parent cell (a process known as replication). This will result in the exact two copies of the parent genetic material. The resultant copies of DNA are attached to the plasma membrane of the parent cell. The replication is bi-directional, it means it moves along both the strands simultaneously from the origin. Even, the origin point of the replication is near to the binding site of genetic material to the plasma membrane.
  • Now the cell grows, along with increasing the distance between the two copied chromosomes that are attached to the plasma membrane.
  • Gradually the septum (which is a new cell wall) also begins to grow, across the middle of the separating cells and thus completely dividing them into two. As amoeba does not have a cell wall, so a cleavage furrow is developed that separates the two dividing cell in equal half.
  • Now, after the formation of a septum, each cell is an individual cell, whether they get separates completely or not, as it is seen in some microbes that even after the formation of septum they remain attached to each other.

Point to note is that, There is the protein known as FtsZ protein, that forms the ring ‘FtsZ ring‘ that trigger the other proteins for the formation of the new cell wall and acquire the materials required for the formation of the new septum or cell wall. Secondly, along with the division of the genetic material, the cytoplasmic material is also divided and transferred to the daughter cells, in order to sustain its life.

Therefore, the result of binary fission is that one parent cell gives rise to two daughter cell and then each daughter cell repeats the same process by giving rise to another two-cell, then four, eight and so on.

The process is very rapid and is frequently performed with an interval of every 15 minutes, like in E.coli.; although it can be as slow as Mycobacteria leprae (causing leprosy) that divides only once in two weeks.

As, binary fission is so rapid and always result in the cells that are clones (genetically identical) of their parent cells, and hence does not provide any ray for genetic diversity, variation or recombination and can lose their identity and resulting in extinction as to cop with the changing environment, there is a need of variation. Therefore, the genetic transfer in prokaryotes takes place by the other three methods, that support the organisms in their survival ship.

Genetic transfer

There are three main ways for the genetic transfer, these are transformation, transduction and conjugation. In these methods, the organisms take the pieces of DNA from the environment and get exchange with the other prokaryotic organisms.

In transformation, the one prokaryote takes up the DNA from the environment which is been shed off by the other prokaryotes. In transduction, the prokaryotes get infected by the virus, that works by injecting a small part of DNA taken from another bacterium. In conjugation, there is the temporary fusion between the organisms, for the exchange of the genetic material, it is considered as the part of sexual reproduction.

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