Introduction

The three domains of life are the broadest biological categories for cellular progression. Carl Woese and colleagues proposed the three-domain system in 1990, which separates cellular life forms into archaea, bacteria and eukaryotic domains. The three domains of living things add a classification level to the previously utilized five- or six-kingdom systems. As Archaea appear to be more closely connected to Eukaryotes than other prokaryotes, this categorization scheme recognizes the fundamental split between the two prokaryotic groupings. The three domains of life show how cellular change has progressed over time. They all have the same ancestor, the Last Universal Common Ancestor (LUCA).

The discovery of three domains of living things

There were five Kingdoms in all, namely- Animalia, Plantae, Fungi, Protista and Bacteria.

Eukarya and Prokarya were the two main classifications for the five kingdoms. New knowledge of molecular biology has altered this perspective on life. Long thought to be bacteria, a form of a prokaryotic organism has been discovered to have substantially distinct DNA from bacterial DNA. This distinction prompted University of Illinois scientist Carl Woese to suggest restructuring the Tree of Life into three Domains of living things: Eukarya, Eubacteria (natural bacteria) and Archaea.

Let us know the details of each of the three domains of life

1. Eukarya: The domain Eukarya is made up of organisms with a “true nucleus,” as defined by the Greek words “EU” and “karyon,” which mean “true” and “nucleus” respectively.

The kingdoms of Eukarya are classified into four groups:

• Protists are eukaryotic creatures that are primarily unicellular and simple
• Fungi are multicellular or unicellular creatures that have eukaryotic cell types
• Plants: multicellular organisms that are made up of eukaryotic cells
• Animalia Kingdom: Eukaryotic cells make up multicellular organisms known as animals

2.   Archaea: Sequence study of highly conserved macromolecules indicated Archaea as one of three major lineages of current cellular life. Archaea have some traits of bacteria, some characteristics of eukaryotes and some unique properties, which is consistent with their status as the third form of life.

Archaeal creatures include the following:

• Methanogens 
• Halophiles
• Thermoacidophiles 

3. Bacteria: The prokaryotes that individuals encounter daily are classified as domain Bacteria. Most bacterial species are heterotrophic, meaning they feed on organic substances. Bacteria comprise the following types:

• Photosynthetic bacteria 
• Spirochaetes
• Bifidobacterium 

Three domains of life characteristics

The three domains of life characteristics can be separately stated as under–

1. Eukarya

• The division of cells are different: Rather than simply dividing and copying their genetic contents (like other domains do), eukaryotes divide their cells through two processes: mitosis and cytokines
• Double membrane nucleus: The nuclear envelope, a bilayer membrane with holes, surrounds the nucleus of eukaryotes, allowing DNA to travel in and out
• Membrane-bound organelles: The “organelles” are diverse internal membrane-bound structures seen in eukaryotic cells. Organelles in cells are responsible for carrying out physiological and metabolic functions critical to the cell’s survival. Other organelles provide support and motility. Intracellular filaments, cilia and flagella were examples

2.   Archaea

• They are prokaryotic cells, but their genetic makeup is closer to eukaryotes
• Ether connections connect branched hydrocarbon chains to glycerol in cellular membranes
• Peptidoglycans, polymers made composed of sugars and amino acids, are absent from Archaea cell walls
• While archaea do not respond to some drugs that bacteria do, they respond to antibiotics that cause eukaryotes to become ill
• Archaea have ribosomal ribonucleic acid (rRNA) unique to archaea and are required for protein synthesis. It is distinguished from rRNA found in bacteria and eukarya by molecular areas that are noticeably different

3. Bacteria

• Bacteria are single-celled organisms
• They are devoid of organelles like chloroplasts and mitochondria and the actual nucleus seen in eukaryotic cells
• A nucleoid contains DNA, which is a continuous and circular double strand
• Bacteria have  peptidoglycan cell walls
• Binary fission or the breaking of a bacterial cell after it reaches a specific size, is used for reproduction

Comparison and contrast of three domains of life

Similarities

• DNA is the hereditary substance in all three realms
• They all have membranes made of phospholipids and use protein catalysts (enzymes) to speed up metabolic processes
• Protein synthesis is carried out by RNA and ribosomes
• Asexual reproduction is possible in archaea and eukarya. The process of translation and transcription in Archaea is identical to that of Eukaryota
• Bacteria and Archaea are prokaryotes, single-celled creatures that lack a nucleus

Differences

• The Eukarya are distinguished from the Archaea and Bacteria by their eukaryotic cells, which have a membrane-enclosed nucleus and other membrane-enclosed organelles
• The ribosomal RNA (rRNA) sequence of Eukarya is distinct from that of Archaea and Bacteria
• Bacteria have no nucleus in their cells. Archaea have a distinct cell wall than bacteria and do not have a nucleus. Eukaryotes have a nucleus

Conclusion

Scientists have sequenced the whole genomes of several distinct species from the domains Bacteria, Archaea and Eukarya in the last few years. Scientists have compared how thousands of genes differ or are similar among creatures from the three domains because of this wealth of information. Each of the three cell types fits into recurring tasks or specialities. At least in mild settings, bacteria are the most prolific reproducers—extreme conditions, such as high temperatures, high acids and sulphur, cause archaeans to adapt swiftly. Adapting to a wide range of food sources is part of this. Like , multicellular organisms like humans are most adaptable. Eukaryotes are the most adaptable when it comes to cooperative building colonies.