Three primary kingdoms

All living cells contain ribosomal RNAs, and it seems that these nucleic acids have changed very little in the course of evolution because their structures are similar in all organisms. Despite this enormous molecular uniformity, however, all species are slightly different in their ribosomal RNAs, and in 1977 Carl Woese showed that these little differences give us precious information on the very first stages of cellular evolution. 

Woese chose to study the RNAs of the small ribosomal subunits having extracted and purified these long molecules, he cut them at 

At the moment, there is no agreement about the names of the other 

Archae Eubact Eukar Archae Eubact Eukar 

Archae Eubact Eukar Eubact Archae Eukar 

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The experimental data that prove the existence of the three primary kingdoms do not tell us much about the last common ancestor, but we can still say that such a progenitor must have existed, because all cells of the three kingdoms have the same genetic code, the same metabolic currency based on ATP, and roughly 50% of bacterial genes have homologues in eukaryotes. 

The three primary kingdoms of cells are Eukaryotes, Bacteria, and Archae. 

Figure l. The universal unrooted phylogenetic tree showing three distinct primary kingdoms Eubacteria, Archaebacteria and Eukaryotes (from Woese 1987a). 

Halobacterium salinarum is a member of the domain Archaea. Some representative organisms of the modern kingdoms are shown in Figure 135.1. Based on sequence analysis of ribosomal RNA genes, life on earth was divided into three primary lineages (domains) Eukarya, Bacteria, and Archaea. Archaea is... 

The primary benzene producers in the United Kingdom ate Shell Chemicals UK, Imperial Chemical Industries PLC, and BP Chemicals Ltd. These three companies have a combined armual capacity of over 1,100,000 t. 

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