Table of Contents
What are Prokaryotic Cells?
Microorganisms are broadly characterized as prokaryotes and eukaryotes, where both the classes differ from each other in their characteristic, structure, shape and the type of microorganisms they contain. Prokaryote is a Latin word, which when broken into two half means pro – before and kary– nut.
Thus, Prokaryotic cells can be defined as the one which do not contain nucleus and are devoid of various organelles as they lack internal membranes and thus their functioning isn’t that complex when compared to eukaryotes. As they lack nucleus, the genetic material is encapsulated in a region called the nucleoid.
Prokaryotic cells lack organelles and organelles such as mitochondria, chloroplast and nucleus, they are said to be unicellular.
The DNA encapsulated in the nucleoid region of the cytoplasm is single stranded circular DNA, where the mode of reproduction is asexually through budding and binary fission.
In eukaryotes, sexual type of mode of reproduction is seen such as conjugation. Even if the prokaryote lack several organelles, it contains other structures and organelles.
Prokaryotic cells have a protein called Flagellin which is required for chemotaxis which will provide support to the bacteria. Other prokaryotic organelles are thylakoid systems, carboxysomes, ribosomes and magnetosomes.
The function of chlorosomes is to harvest light in green sulphur bacteria.
Carboxysomes as the name suggest fixes carbon content in bacteria. Magnetosomes are seen in magnetotactic bacteria. In photosynthetic bacteria, thylakoids could be seen. Example, cyanobacteria.
Very few prokaryotes contain a cell wall which is made up of peptidoglycan which determines the gram positive or gram negative of the bacteria depending on the thickness of the cell wall.
Thicker cell wall is found in gram positive bacteria whereas gram negative have an outer membrane along with a thin peptidoglycan layer. Archae lacks peptidoglycan layer and has pseudopeptidoglycan.
Prokaryotes vs Eukaryotes
The genetic material of prokaryotes is inside the nucleoid region of the cytoplasm whereas in eukaryotes its located within a double bound nucleus and the rest could also be found in the chloroplast and in the mitochondria if possessed. The energy source in both prokaryotes and eukaryotes is ATP and the genetic materials details are present in the genes for both.
The chromosome is circular for prokaryotes and linear for eukaryotes. As prokaryotes lack various organelles, they are smaller in size whereas eukaryotes are larger in size, thus prokaryotes have quick metabolic and growth rate.
Ribosomes are present in both eukaryotes and prokaryotes serving the function of protein synthesis; however, they differ in their subunit. The prokaryotic ribosome is 70S which has a larger sub unit of 50S and a smaller subunit of 30S. The eukaryotic ribosome is 80S, where the 60S is the larger one and 40S is the smaller one.
Bacteria, archae and cyanobacteria are the examples of prokaryotes whereas examples of eukaryotes are fungi, virus, protist and etc.
Examples of Prokaryotic Cells
a) Bacteria: Belonging to the domain eubacteria, bacteria are single celled and invisible without the aid of microscope. The DNA is encapsulated in the nucleoid region of the cytoplasm and these organisms lack compartments. The reproduction mode is asexually through budding or by releasing spores. These organisms can thrive in various conditions such as in extreme heat, extreme cold, soil, water, hot water springs, deep sea and etc. The types of bacteria could be cocci, bacilli, coccobacilli, spirilla, vibrio and etc.
b) Archaea: These organisms are also devoid of nucleus, of the domain Archaea and vary from eukaryotes and bacteria, however their genes quite replicate that of eukaryotes and possess various enzymes that are useful in transcription, translation and other pathways. These organisms can also survive in various conditions such as in salty climate, hot conditions, and in places where methane is been produced.
c) Cyanobacteria: Commonly known as the blue green bacteria or photosynthetic bacteria. They are derived from protists and are now place in a separate class of photosynthetic bacteria. They are found in soil, water and are economically very important as a large percent of oxygen we get is due to them. They have organelles such as carboxysomes, thylakoids and phycobilins which are the photosynthetic pigment, which gives them color. Examples include Nostocales, Pleurocapsales and Stigonoematales.
Prokaryotic Cells Citations
- Functional inclusions in prokaryotic cells. Int Rev Cytol . 1988;113:35-100.
- Macromolecule diffusion and confinement in prokaryotic cells. Curr Opin Biotechnol . 2011 Feb;22(1):117-26.
- How do prokaryotic cells cycle? Curr Biol . 2004 Sep 21;14(18):R768-70.
- Prokaryotic cells: structural organisation of the cytoskeleton and organelles. Mem Inst Oswaldo Cruz . 2012 May;107(3):283-93.