Definition
A prokaryotic cell is a type of cell that does not have a true nucleus or membrane-bound organelles. Organisms within the domains Bacteria and Archaea are based on the prokaryotic cell, while all other forms of life are eukaryotic. However, organisms with prokaryotic cells are very abundant and make up much of Earth’s biomass.
Characteristics of Prokaryotic Cell
Prokaryotic cells have different characteristic features. The characteristics of the prokaryotic cells are mentioned below.
They lack a nuclear membrane.
Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent.
The genetic material is present on a single chromosome.
The histone proteins, the important constituents of eukaryotic chromosomes, are lacking in them.
The cell wall is made up of carbohydrates and amino acids.
The plasma membrane acts as the mitochondrial membrane carrying respiratory enzymes.
They divide asexually by binary fission. The sexual mode of reproduction involves conjugation.
Prokaryotic Cell Structure
A prokaryotic cell does not have a nuclear membrane. However, the genetic material is present in a region in the cytoplasm known as the nucleoid. They may be spherical, rod-shaped, or spiral. A prokaryotic cell structure is as follows:
Capsule– It is an outer protective covering found in the bacterial cells, in addition to the cell wall. It helps in moisture retention, protects the cell when engulfed, and helps in the attachment of cells to nutrients and surfaces.
Cell Wall– It is the outermost layer of the cell which gives shape to the cell.
Cytoplasm– The cytoplasm is mainly composed of enzymes, salts, cell organelles and is a gel-like component.
Cell Membrane– This layer surrounds the cytoplasm and regulates the entry and exit of substances in the cells.
Pili– These are hair-like outgrowths that attach to the surface of other bacterial cells.
Flagella– These are long structures in the form of a whip, that help in the locomotion of a cell.
Ribosomes– These are involved in protein synthesis.
Plasmids– Plasmids are non-chromosomal DNA structures. These are not involved in reproduction.
Nucleoid Region– It is the region in the cytoplasm where the genetic material is present.
A prokaryotic cell lacks certain organelles like mitochondria, endoplasmic reticulum, and Golgi bodies.
Components of Prokaryotic Cells
The prokaryotic cells have four main components:
Plasma Membrane- It is an outer protective covering of phospholipid molecules which separates the cell from the surrounding environment.
Cytoplasm- It is a jelly-like substance present inside the cell. All the cell organelles are suspended in it.
DNA- It is the genetic material of the cell. All the prokaryotes possess a circular DNA. It directs what proteins the cell creates. It also regulates the actions of the cell.
Ribosomes- Protein synthesis occurs here.
Some prokaryotic cells possess cilia and flagella which helps in locomotion.
Reproduction in Prokaryotes
A prokaryote reproduces in two ways:
Asexually by binary fission
Sexually by conjugation
Binary Fission
The DNA of an organism replicates and the new copies attach to the cell membrane.
The cell wall starts increasing in size and starts moving inwards.
A cell wall is then formed between each DNA, dividing the cell into two daughter cells.
Recombination
In this process, genes from one bacteria are transferred to the genome of other bacteria. It takes place in three ways-conjugation, transformation, transduction.
Conjugation is the process in which genes are transferred between two bacteria through a protein tube structure called a pilus.
Transformation is the mode of sexual reproduction in which the DNA from the surroundings is taken by the bacterial cell and incorporated in its DNA.
Transduction is the process in which the genetic material is transferred into the bacterial cell with the help of viruses. Bacteriophages are the virus that initiates the process.
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