What are the three Domain system of classification based on the difference in 16s rRNA?

Explanation

Three domain classification was proposed by Carl Woese (1977) and his co-workers. They classified organisms based on the difference in 16s rRNA genes. The three domain system adds the taxon 'domain' higher than the kingdom.

Domain Archaea:
1. Single celled organisms, the prokaryotes which have the ability to grow in extreme conditions like volcano vents, hot springs and polar ice caps, hence are also called extremophiles.
2. Capable of synthesizing their food without sunlight and oxygen by utilizing hydrogen sulphide and other chemicals from the volcanic vents.
3. Some of the them produced methane (methanogens).
Domain Bacteria:
1.Bacteria are prokaryotic, their cells have no definite nucleus and DNA exists as a circular chromosomes and do not have histones associated with it.
2. Do not possess membranc bound organelles except for ribosome (70S type). Their cell wall contains peptidoglycans.
3. Many are decomposers, some are photo-synthesizers and few cause diseases. There are beneficial probiotic bacteria and harmful pathogenic bacteria.
4. The Living World Cyanobacteria are photosynthetic blue-green algae which produce oxygen. It played a key role in the changes of atmospheric oxygen levels from anaerobic to acrobic during the early geologic periods.