The cell can be defined as biological unit (or) the structural and functional unit of life. The cell is the Latin word, which means a small room. A scientist named Robert Hooke, observed and coined the term cell in the year 1665.
Prokaryotes can be defined as the group of organisms, which lacks their cell nucleus. Organisms, with this cell type are known by the term prokaryotic organisms (or) prokaryotes. These prokaryotic organisms are the first organisms to be found in our planet earth. There are two types of prokaryotes:
Below you could see characteristics of prokaryotes
- They are single celled organisms and are much smaller compared to eukaryotic cells.
- They are unicellular and their size ranges from 1 µm and 10 µm but in a few cases they may vary in their size from 0.2 µm to 750 µm.
- Prokaryotic organisms exist in different shapes, which includes spherical, rod, flat, coccus, bacillus, spirochete and some of them are shapeless as they do not possess constant shape.
- They consist of very few internal structures like cell wall, ribosome, plasma membrane, cytoplasm along with circular strands of DNA.
- They have a cell wall, which are made up of peptidoglycan.
- Locomotion – There are only few prokaryotes, which can move, swim, spin and rotate with the help of the helical shaped membrane called flagella, while others are non motile.
- Nutrition – There are four modes of nutrition, which includes –
- Phototrophs: They are photosynthetic prokaryotic organisms, which synthesize their own food by using light energy form the atmosphere.
- Chemotrophs: The prokaryotic organisms, which prepares its own food by the process of chemosynthesis.
- Heterotrophs: The prokaryotic organisms, which depends on other substances for nutrition as they cannot synthesize their own food.
- Reproduction – They generally reproduce asexually by binary fission, conjugation, transduction and transformation.
A prokaryotic cell is mainly composed of cell wall, plasma membrane, cytoplasm, genetic material in the nucleiod and ribosome.
- The prokaryotic cell wall protects the cell organelles and provides the shape to the cell. The cell wall is of two types - Gram positive cell wall and Gram negative cell wall.
- The plasma membrane of a prokaryotic cell acts as a selective permeable membrane and also regulates the functioning of input and output of a cell.
- The cytoplasm of a prokaryotic cell plays a vital role in protecting a cell by separating cell organelles from each other.
- The genetic material of a prokaryotic cell contains the DNA of a prokaryotic organism, which are circular and it is stored in the nucleiod.
- The ribosome of a prokaryotic cell plays a vital role in protein synthesis of a cell.
Examples of Prokaryotes
Bacteria, blue green algae and E.coli are a few examples of prokaryotic organisms.
Photosynthesis is the biological processes that are mainly seen in all green plants and in few photosynthetic prokaryotes like photosynthetic bacteria. This process uses solar energy and carbohydrates.Photosynthetic prokaryotes are the organisms that can synthesize their food in the same process as the plants prepare. Cyanobacterium, green and purple sulphur bacterium are the example for photosynthetic prokaryotes.
In this organism the reaction of photosynthesis is in bacterial plasma membrane. During the process of photosynthesis the water molecules are split and oxygen molecules are received as a byproduct.
The equation of photosynthesis is:
Energy + 6CO2 + 6H2O $\rightarrow$ C6H12O6 + 6O2
The ribosome in prokaryotes helps in building proteins from amino acids in the cytoplasm of a cell. They are found freely floating in a cell and are attached to the endoplasmic reticulum of a cell. The ribosomes in prokaryotes are made up of RNA.