Three Domains of Life: Characteristics and Differences

The earth is 4.6 billion years old and microscopic life is considered to have primarily arisen around 3.8 and 3.9 billion years ago. Microbes exclusively accounted for 80 percent of the earth’s history. Microbial life is still the most common kind of life on the planet. There have been numerous attempts to categorize living beings since the birth of humanity.

Prior to the discovery of the three domains of cellular life, life on the planet was divided into two groups: Prokaryotae or Monera and Eukaryotae. Animals, plants, fungi and protists were classified as eukaryotae, whereas bacteria were classified as Prokaryotae or Monera.

Carl Woese, an American scientist and physicist, split Prokaryotae into Archaea and Bacteria in 1990. The division of Prokaryotae into Archaea and Bacteria is owing to the belief that none of them are ancestors of the other. While they have certain common characteristics, they also have some unique characteristics.

As a result, the three-domain system, also known as the three-domain system of life or 3 domains of living things, was created to divide life on the planet into three distinct domains: Archaea, Bacteria and Eukaryote. It is, in essence, a biological categorization of the three domains of life-based on distinctions in their 16S rRNA genes.

Three domains of life characteristics:

The existence of a nuclear membrane distinguishes the Eukarya domain from the Archaea domain and the Bacteria domain, both of which lack one; the Archaea and Bacteria domains are distinguished by biochemistry and RNA markers. Each one of the three domains of life identified by scientists presently has rRNA that is distinct to them, and this information alone lays the groundwork of a three-domain system. A six-kingdom system of life exists in addition to the three-domain system, namely Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia.

Archaea Domain:

Archaea are prokaryotic organisms with membranes made up of branched hydrocarbon chains connected to glycerol through ether bonds. These ether-containing connections enhance archaea’s capacity to tolerate severe temperatures and very acidic environments. The finest examples of Archaea include severe halophiles and hyper-thermophiles. The halophiles are the organism that lives in an extremely salty environment, whereas the hyper-thermophiles are the organisms that flourish in excessively hot conditions.

Bacteria Domain:

Despite the fact that bacteria like Archaea are prokaryotic cells, their membranes consist of unbranched fatty acid chains connected to glycerol by ester bonds. Bacteria such as cyanobacteria and mycoplasmas are the most common. They are classified as a distinct category since they lack ether-containing connections like Archaea and hence a separate domain. There is so much diversity in this area that determines the number of species of bacteria that exist on the earth is nearly difficult.

Eukarya Domain:

Eukaryotes are eukaryotic cells with membranes that are comparable to those of bacteria, as the name indicates. Eukaryotes are further divided into the following categories:

1. 1. Kingdom Protista– Algae and protozoans belong to this kingdom
   2. Kingdom Fungi– Yeast and mold belong to this kingdom
   3. Kingdom Plantae– It is the kingdom of blooming plants and ferns
   4. Kingdom Animalia– Insects and vertebrates are members of the Animalia kingdom

Eukaryotes do not all have a cell wall, and if some do, it does not include the peptidoglycan seen in bacteria. While cells in both kingdom Plantae and kingdom Animalia are arranged into tissues, cell walls are only found in kingdom Plantae.

Compare and contrast the three domains of life:

The Archaea:

Methanogens, halophiles and hyper-thermophiles are among the archaea that exist in harsh settings. One explanation for this is that ether-containing links in Archaea membranes are more durable than ester-containing linkages in Bacteria and Eukarya membranes, allowing them to survive greater temperatures and acid concentrations.

• They are prokaryotic cells

• Archaea have no peptidoglycan in their cell walls

• Archaea have membranes made up of branching hydrocarbon chains connected to glycerol by ether bonds contrasting Bacteria and Eukarya. In some, hydrocarbon chains may contain rings

• Some drugs that affect bacteria are ineffective against Archaea, yet some antibiotics that target Eukarya are effective

• Archaea has rRNA that is unique to the Archaea. It is evident by the fact that molecular areas that are dissimilar to Bacteria and Eukarya rRNA, exist

The Bacteria

Cyanobacteria, Mycoplasmas, Gram-positive bacteria, and Gram-negative bacteria are among the bacteria.

• They are prokaryotic cells
•  Bacteria, like the Eukarya, have membranes made of unbranched fatty acid chains connected to glycerol by ester bonds

• Bacteria have peptidoglycan in their cell walls, unlike Archaea and the Eukarya

• Traditional antibacterial medicines are effective against bacteria. However, most antibiotics that attack Eukarya are ineffective

• Bacteria have their own rRNA, as evidenced by the presence of molecular areas that are dissimilar to those found in Archaea and Eukarya

Eukaryotes

• They have eukaryotic cells

• Eukarya are resilient to typical antibacterial drugs but susceptible to most antibiotics that target eukaryotic cells; nevertheless, not all Eukarya have cells with a cell wall, and even those that have a cell wall do not contain peptidoglycan

• Eukarya have their own rRNA, as evidenced by the existence of molecular areas that are dissimilar from those found in Archaea and Bacteria