The type of cells that do not have a well-defined nucleus and no membrane-bound organelles are known as prokaryotic cells. Organisms with prokaryotic cells are called prokaryotes and they are generally single-celled microorganisms. These organisms can be free-living or can be found in the gut of animals. The size of a prokaryotic cell can range between 0.2 to 10 microns.
Examples of prokaryotic cells include bacterial cells, which have different shapes and structures and possess extrachromosomal DNA known as a plasmid. Archaeal cells which are similar to bacterial cells, are found in extreme environments such as hot springs and also in soil and marsh. These single-celled organisms also possess plasmids.
Prokaryotic Cell Structure
Prokaryotic cells are not complex structures. They do not have a true nucleus and the genetic material is not contained within a membrane but it is seen as coiled in the cytoplasm of the cell. Below is a list of structures that can be observed in a prokaryotic cell.
-
Cytoplasm: It is a gel-like substance that is mainly composed of water and contains various cellular components, enzymes, organic molecules, and salts.
Major Components of the Prokaryotic Cell
-
Glycocalyx: In some prokaryotic cells it is a part of the cell envelope or capsule and is composed of macromolecules.
-
Mesosomes: These are extensions of the cell or plasma membrane in the form of lamella or tubules. Their functions are:
-
Assisting in cellular respiration and secretion.
-
Cell wall formation.
-
Increasing the surface area of enzymatic content and plasma membrane.
-
Genetic material replication and distribution in daughter cells.
-
Inclusion bodies: They are free bodies observed in the cytoplasm of a prokaryotic cell and act as storage units for reserve materials.
-
Chromatophores: These membrane extensions are specifically found in cyanobacteria and have photosynthetic pigments inside.
All bacterias are prokaryotes and the above-mentioned structures can be seen in all bacterial cells.
The Different Types of Prokaryotic Cells
Prokaryotic Cellular Organisms or Prokaryotes can be Divided into Two Domains:
|
Archaea |
Bacteria |
|
Archaea can be subdivided into
|
Bacteria can be subdivided into
|
Features of Prokaryotic Cells
Important Characteristics of Prokaryotic Cell
-
The absence of clearly-defined membrane-limited organelles such as Golgi complex and mitochondria.
-
Histone proteins that are essential for the formation of chromosomes in the eukaryotic cells are absent.
-
The mitotic apparatus and the nucleolus are absent.
-
The cell membrane below the cell wall is produced into the cytoplasm and acts as the mitochondrial membrane to carry respiratory enzymes.
Reproduction in Prokaryotes
Reproduction in a prokaryotic cell takes place in two ways
-
Binary fission: The process starts with the replication of the DNA molecule and two copies of the molecule attach themselves to the cell membrane.
-
Then the cell membrane begins to grow between the two molecules and once the cell is twice its original size the cell membrane begins to pinch inwards.
-
Afterwards, a cell wall forms between the two DNA molecules which divides the original cell into two identical daughter cells
-
Recombination: The genes of one cell are transferred to the genome of another cell. The process takes place in three ways
-
Conjugation: The process of gene transfer takes place between two cells through a protein tube-like structure called a pilus.
-
Transformation: It is a type of sexual reproduction where the cell takes genetic material from the surroundings and incorporat
es it into its genetic material. -
Transduction: In this process, the genetic material is transferred to another cell with the help of viruses.
Conclusion
“Prokaryotic cell” is one of the most important chapters in biology. So, a student needs to prepare on this topic very nicely to score good marks. For any doubt you can download the study materials by registering at .com.